Servo20201.Pdf
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20 Bots in Brief
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• Do the Worm SERVO Magazine (ISSN 1546-0592/CDN Pub Agree#40702530) Issue-1 (Jan-Feb) is published • Draganfly Drones Do Monitoring 6X a year for $26.95 per year by T & L Publications, Inc., 2279 Eagle Glen Parkway, #112-481, Corona, CA 92883. Periodicals postage PAID at Corona, CA and at additional entry mailing • Follow the Bouncing Ball offices. POST MASTER: Send address changes to SERVO Magazine, 2279 Eagle Glen Parkway • Gonna Burst Your Bubble #112-481, Corona, CA 92883 or Station A, P.O. Box 54, Windsor ON N9A 6J5; cpcreturns@ servomagazine.com. 4 SERVO Issue-1.2020 07 Grant Imahara Eulogy by David Calkins Page 46 10 Experimenting with Walking Robots — Walking Up and Down Hills by John Blankenship This series of articles has explored many aspects of walking robots from the unexpected side effects of various movements to the need for sensors and how to utilize them. This final installment utilizes many of the principles discussed to create a robot that can navigate inclines as easily as level terrain. 16 Goal Prediction Using AI by Rajat Keshri 54 Versatile Stepper Control Learn the basics of machine learning and the power of by William Cooke what machine learning can do. This article teaches the Stepper motors are a staple of robotics. They’re great for implementation of different machine learning algorithms for precise speed and positioning. It’s also easy to control one. predicting a simple binary classification. It’s mainly focused But what about two, or three? With different step rates? on beginners who are very new to machine learning. As an For different amounts of time? While your microcontroller application to apply what you learn, you’ll discover how to continues doing other tasks? It can quickly become use different algorithms on predicting if a goal has been difficult, but with the technique presented here you can scored or not. do all that and use only about two or three percent of the microcontroller’s time. 38 Build Your Own Computer- Controlled Three-Axis Robotic Arm 61 Laser Alignment System for by Sam DiPietro, Brett Sawka, and Rohan Shah Your CNC Router Having a passion for art but no artistic skill, three by Roger D. Secura engineering students built a contour image plotter known In this article, I’ll show you how to build a laser power as “Bot Ross.” This article explains the design of Bot Ross’s supply circuit and a special bracket for your CNC router hardware and software as well as its intended operation. motor so that you’ll be able to consistently find the edges of your workpiece. You’re going to like the fact that the power 46 Building a Linear Actuator supply circuit we’ll make only requires three components: by Theron Wierenga the LM317T voltage regulator and two resistors. While doing some thinking about building a walking bird robot, I researched purchasing linear actuators. What I 66 Alpha-Writer: A Computer- found is that linear actuators are fairly expensive — especially Controlled Letter Writing Robotic if you’re an amateur robot builder with a limited budget. This led me to thinking about what it would take to build my Arm by V S Rajashekhar own linear actuators. In this DIY project, I’ll show you how to make a simple computer-controlled letter writing robot from scratch. It has two revolute joints connecting two links and at the end of the robot, there’s an end effector with a pen. By pressing a button on a screen, you can tell the robot which letter to do next. It can write all 26 letters of the alphabet. 70 Appetizer: Connected Cars — A Fast Brewing World in Automotive by Abhinav Kumar There’s a huge ecosystem of connected car services and mobility services startups, technology giants, consulting Page 54 companies, and finally, automotive OEMs that are working tirelessly to modernize the way we commute. SERVO Issue-1.2020 5 PUBLISHED BY Mind / Iron T & L Publications, Inc. CONTACT by Bryan Bergeron, Editor 2279 Eagle Glen Pkwy #112-481 Corona, CA 92883 OFFICE: (951) 371-8497 An Analog Artifact Worthy FAX: (951) 371-3052 www.servomagazine.com
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CONTRIBUTING EDITORS Kevin Berry John Blankenship William Cook V S Rajashekhar Roger Secura Rohan Shah Sam DiPietro Brett Sawka Rajat Keshri Abhinav Kumar t my first real job with a I, on the other hand, lusted Theron Wierenga Ryan Clingman Nate Franklin David Calkins communications company, after one of the new digital meters Aevery technician was equipped on the market. After all, why settle WEBSTORE MARKETING/ with a piece of state-of-the-art test gear for a reading of only 2-3% full COVER GRAPHICS designed to function in the harshest scale accuracy, when a DMM could Brian Kirkpatrick environments and with literally theoretically take a reading with double [email protected] constant abuse. Of course, I’m talking the accuracy and to several digits and about the Simpson 260, easily the with a much higher input impedance? Copyright © 2020 by T & L Publications, Inc. most popular analog VOM (volt-ohm Putting aside the issues of settling All Rights Reserved meter) of all time. time, need for frequent calibration, All advertising is subject to publisher’s approval. We are not responsible for mistakes, misprints, The best technicians and and the need to be near a 110V or typographical errors. SERVO Magazine engineers wouldn’t consider anything outlet, when digital meters first hit the assumes no responsibility for the availability else to assist them in diagnosing market, they were cool. They were like or condition of advertised items or for the and maintaining microwave having one of the first iPhones to hit honesty of the advertiser. The publisher makes communications gear. I remember the street. no claims for the legality of any item advertised in SERVO. This is the sole responsibility of the the best of the engineers could read Over the years, I worked through advertiser. Advertisers and their agencies agree a dozen values in only a few seconds. several generations of DMMs, ranging to indemnify and protect the publisher from They could accurately estimate values from $10 to over $800. I even any and all claims, action, or expense arising long before the Simpson’s needle considered the digital Simpson — a from advertising placed in SERVO. Please send all moved into final position, simply based short-lived abomination. My current editorial correspondence, UPS, overnight mail, and artwork to: 2279 Eagle Glen Pkwy #112- on the initial velocity of the needle. toolkit includes a portable Fluke 87 481, Corona, CA 92883. 6 SERVO Issue-1.2020 Grant Masaru Imahara DMM and a benchtop Fluke 45 DMM. Other than changing batteries and October 23, 1970 – July 13, 2020 leads, these DMMs have been trouble- free and a cornerstone of my repair work. So, why did I add a Simpson 260 to my arsenal, especially when — on specifi cations alone — a DMM with similar capabilities can be had for 5% of the price of a used Simpson 260? I have to admit the reason is partly nostalgia. After all, handling the 3 lb over-sized Bakelite case and the solid “click-click” rotary switch is pure pleasure. Instead of a series of cold LED or LCD numbers, my measurements are based on a crisp black needle defl ected across a colorful mirrored background. My reason for acquiring the Simpson 260 (Simpson 260 8p, used, with leather case, $175, eBay) is also partly practical. Measuring the voltage across and current through motors and other actuators is simply easier with an analog meter. The analog meter movement is relatively immune to higher frequency noise and spurious by David Calkins signals, making measurements a lot easier. henever we talk about the famous, we call them “stars.” In fact, I’ve found the Simpson The dots of light in an otherwise black sky. However, stars performs well in just about every aren’t the only things in the night sky. About once in our task previously covered by my Fluke Wlifetime, we get to see something even bigger and more DMMs. If I could talk with the Simpson memorable — we are graced with a comet. designers, the only change I’d suggest A comet isn’t just one point of light in the sky. It fl ies across the is to supplement the current DCV full stars leaving a giant trail of lights. That was Grant. It wasn’t enough scale ranges of 2.5V, 10V, 25V, 50V, that he should be a dot in the sky. Everywhere he went, he made 250V, 500V, and 1000V with 3.5V and sure that there was a streak of countless glowing points following in 5.0V or 6.0V. Even so, the 10V full his wake. Comets are rare and bring with them wonder and magic. scale range is suffi cient for both 5V You know they’re special the second you see them. and 3.3V circuits. I fi rst met Grant in 2000, and I knew he was special. We were If you’re convinced that an analog just chatting about the nascent fi eld of robots, and he listened to artifact is in your future, the cost of everything I had to say. He was one of the few people I’ve ever met entry is between $50 and $200 used, that really cared about your opinions. He wasn’t just waiting for his depending on model and condition, turn to talk. He wanted to learn from you, about you, and what you and $350 new (Simpson 260-8p, could share with him. Amazon). When he did talk, it was invariably about ideas or other people. A point to consider is that, unlike Never himself. We bonded over a similar upbringing by single moms your digital meters and lesser analog without a strong male infl uence. Which is an all too common thing. VOMs, even an older Simpson is likely But Grant didn’t just discuss it casually. He was immensely grateful to outlast you. SV to his mother for her hard work in raising him, and he was forever talking her up. How many people actually talk about their moms and how important they are? He was already living the dream, working at ILM and in the incredibly unique position to play both R2-D2 and C-3PO. When The Phantom Menace went into production, he not only got to build and
SERVO Issue-1.2020 7 drive R2, but he frequently put the C-3PO suit on for and everyone in the community. For several years, he public appearances. mentored a high school robotics team, long after most He taught me a lot about transparency in those others who had achieved fame would have pulled days. When he drove R2, he’d keep the R/C behind his away. No matter how tired he was from TV shoots hip and drove blind. Not to show off his crazy driving or how many times he had to cross the Bay Bridge skills (man, could he drive). No. Just the opposite: in a day, he made time for those kids, even donating to hide them. He’d subtly cling to a back wall so considerable money to ensure that they could glow in that people (especially kids) would only see R2. He the night sky as brightly as he did. And so, even more completed the illusion with wonder and amazement. points of light appeared in the sky behind him. He didn’t want the accolades. He wanted to make As his fame grew, so did his generosity. When old people happy. To help them believe the magic. To friends from ILM needed his help on small independent make them shine. And so, a few more points of light projects, he was there for them. Not for the money, were born, and trailed him in the sky. but because he could help them. His kindness and A few years later, he joined Mythbusters. Rather cheerfulness were ever present. Working alongside than shirking the “geek” label, he reveled in it, giving him late at night at FonCo on various projects, he was all of us other geeks a path to follow — unashamed always the one who was the most sparkling of us, no of any labels that people might put on us. He helped matter how late at night (or early in the morning). We drive the societal shift to embracing the inner geek in all shone a bit brighter when we were around him ... us all. and more lights followed him in the sky. While most people might be happy to shine as No matter what time it was, Grant the comet just a popular TV star, Grant didn’t grow distant. He glowed. His smile and optimism were contagious, and continued to help every chance he could with anyone he stood out in a crowd even if you had no idea who
8 SERVO Issue-1.2020 he was. He cracked jokes, slapped you on the back, and and sharing to help people. If you saw his comet saw the good in everyone and everything. He wasn’t streaking across the sky, it was telling you how to good to others to keep up his image. He was kind and make cool stuff and always focused on education. generous to everyone because that was the only way Time is always more precious than money, and he knew how to be. When he helped you, you always Grant was most generous with his time. Even with all knew everything was going to be just fi ne when you the demands of work and travel, he always found time saw him nod and arch his brow. for others. When a close friend was having a Sailor I had the great fortune of being a close enough Moon themed wedding, he spent months making a friend to go out socially with Grant. One night at movie-worthy perfect giant Cutie Moon Rod which lit dinner, as we discussed solemn non-roboty things, a up for the bride. little girl approached the table. Grant never hesitated Even his personal robotics projects weren’t to be and went from being dulled by the discussion’s clouds kept in his living room. He made a replica BB-8 and to glowing and listening to everything she had to say. I a Baby Yoda not so much for himself, but for kids in don’t think it ever occurred to him to shoo her away ... hospitals who needed something to cheer them up. and one more light in the sky was born. How many people who could do that, would? On several occasions, when we geeks would The trail he left — as all comets do — can be seen go out “marauding” (as he called it), he was often more for the countless points of light trailing it, rather approached by fans for photos. He never turned than the single star at the front. There are hundreds anyone down and didn’t just take the photo. Grant of stories of Grant’s generosity, just like the sparkling made sure to thank them for their fandom. To ask dots of light left in a comet’s wake. He was rare and them about their lives. And to truly listen to them as unique, fi tting seamlessly into whatever group of they shared their hopes and dreams with him (on more people he encountered. But like a comet, his presence than one occasion, the fans got more of him than we in the sky was all too short, but never to be forgotten. did). He stood apart in a fi eld of endless stars, and it’s his At the height of Mythbusters, he called me out of light that will be remembered. the blue to go to dinner. It wasn’t just a casual dinner You’re lucky if you get to see a comet once in your between old friends, but he looked gravely at me and lifetime. Grant was that comet. said, “You know, now that I’ve made it, I want to help When you look up to the sky and you see a comet everyone. What can I do to help RoboGames?” streaking across it followed by an uncountable number This was typical Grant. He could have bought a of twinkling lights, look to see if it has that sly smile bunch of fancy cars and hidden away in a condo on a and an arched brow. beach somewhere, but he never forgot where he came Thanks Buddy. from. So, he MC’d a bunch of events to help everyone. (You can watch one of them at https://youtu.be/ a45qx2bV6JQ. The fi rst 1:26 of him and Kiki is great. You can see his passion and honest excitement. Grant doesn’t appear for the remainder of the clip.) He didn’t just help host. He roamed the pits and made contestants from around the world feel special. He wasn’t basking in his fame. He was a kid in a toy shop. He just knew that he could make things better (even helping teams fi x their robots). And, while helping everyone else, he always made sure that he took care of his mom (which is far more than most of us can say ...). While a lot of stars might turn to product endorsement, Grant only ever used his name to help others (other than the McDonalds thingy ... but most people have forgotten that). He was always teaching
SERVO Issue-1.2020 9 Experimenting with Walking Robots ♦ Part 5
Walking Up and Down Hills This series of articles has explored many aspects of walking robots from the unexpected side effects of various movements to the need for sensors and how to utilize them. This final installment utilizes many of the principles discussed to create a robot that can navigate inclines as easily as level terrain.
ost walking robots built by hobbyists walk by diffi cult; certainly far more diffi cult than I expected. On the transitioning between various static poses; an positive side, walkers provide a very different experience for Mapproach that — while relatively easy — has many hobbyists and when something fi nally works, the process limitations. In addition, affordable walking robots are can be very rewarding. typically powered by inexpensive servo motors which have This fi nal article of the series demonstrates how limited torque for small movements, imprecise repeatability, applying some of the principles discovered during and signifi cant play in their gear trains. A major goal of my experimentation gave my robot the capability to walk on a experimentation with walking robots was to determine ways sloped terrain as well as a fl at surface. of dealing with these limitations. The experimentation also revealed that two walking A Basic Principle robots can be far different from each other when compared with two wheel based robots. This simply means that A basic principle of my walking process is to always techniques that work for one walker might be more or less know where the major joints are currently located, so that successful with another, due to differences in the two robots it’s easy to move to the next position. To that end, my such as the center of gravity, the number of joints, and the software always moves major joints in fi xed increments. Let’s quality of the motors and sensors used. look at an example. Perhaps the most important revelation is that building Suppose we want the robot to take a step of size “D.” a walking robot with hobby-level hardware is extremely It might start by lifting the leg, then extending it. Lifting 10 SERVO Issue-1.2020 By John Blankenship
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the leg could be accomplished by moving the thigh FIGURE 1. Experimenting forward D degrees and the knee backward by the same amount. Note that this would move the leg slightly forward while keeping the foot parallel with the fl oor as shown in the left side of Figure 1. After a short delay, we could extend the calf portion of the leg forward (again by D degrees), but in with Walking order to keep the foot parallel with the fl oor, we also need to tilt the ankle forward by D degrees. Always moving the joints in increments of D degrees makes it easy to keep track of their current location. The problem is that sometimes when you move a robot’s leg, it might not appear to be in the position Part 5 you intended. If the weight of the raised leg, for example, causes the robot to lean forward due to stress on the motors and gear train in the supporting leg, then the extended foot would certainly not be parallel with the ground (see the right side of Figure 1). The left side of Figure 1 looks the way we want the robot to look after the leg is raised, but the variables (names that begin with underscore are global right side is probably how it will actually be with most in RobotBASIC) that will be used to control the walking servomotors. Often, people programming a walking robot routines. Using global variables allows them to be accessed like this will try to adjust the amount the joints are moved to from within RobotBASIC’s sub-routines which utilize local make the robot look like the left side. variables. This minimizes the need to pass parameters that Unfortunately, if the stress is relieved from the are needed by many routines. supporting leg (perhaps by the next movement which Once we know the slope of the fl oor, it can be used to changes the robot’s balance), the robot’s new position will alter the step size (this is basically the D value mentioned be far different than what you’re trying to accomplish. If you earlier). In general, adding the slope of the fl oor to the try to keep the robot posed as expected (rather than always primary step size will cause the robot to step higher when using fi xed movements), then fi guring out how to move to it’s moving up an incline and step lower when it’s going new positions (that might have different balance issues) can downhill. Various parameters such as the lean angle are also quickly become an unmanageable task. set in this routine. The lean angle is how much the robot The best solution is to try to keep the robot balanced, should lean in order to lift the opposing foot from the fl oor. but ultimately, you should simply accept that the robot may You could arrive at parameters like this experimentally or not always appear exactly as expected. If you assume the even have the robot do it autonomously by leaning until the robot’s joints are where they’re supposed to be (no matter foot switches indicate the foot is off the fl oor. how they look) and move them accordingly, the robot — A variable DeltaXtilt is also created that indicates how over time — will generally end up reasonably close to where much the accelerometer readings will change when the you expect. robot leans to one side to take a step. The number is just an approximation, but it works well. We’ll see how these The Code parameters are used shortly. The fi nal action before beginning the walk is that the Figure 2 shows the top levels of my walking code robot will lean its body forward slightly if it’s going up a application. The fi rst sub-routine called in this code is slope and backward if it’s going down. This is not required, FindBalance, which was discussed in Part 4 of this series. It but it does help the robot maintain its balance. causes the robot to autonomously maintain its balance as The Walk routine uses a loop to make right and left the board the robot is standing on is tilted to create an up steps. Before the loop, a call to StartWalk leans the robot to or down slope. An important aspect of this routine is that it the left (based on the variable _LeanAngle). When the fi nal returns the slope of the fl oor (see Part 4 for more details). step is taken, StopWalk leans the robot to the right to return The code in Figure 2 also establishes some global the robot to its normal standing position. SERVO Issue-1.2020 11 Application: gosub InitApplication FIGURE 2. delay 500 // local variables to control walking _DesiredXtilt = 100 // used for balance with arms _DesiredYtilt = 100 _LeanAngle = 12 _PrimaryStepSize = 25 call FindBalance(CurSlope) _CurrentSlope=CurSlope _StepSize = _PrimaryStepSize+_CurrentSlope // Step higher going up hills (lower/down) _DesiredYtilt+=_CurrentSlope _DeltaXtilt = _LeanAngle/5 // adjust body for hill walking call FromCurServoPos(Rthigh,_CurrentSlope) // lean back going down slope call FromCurServoPos(Lthigh,_CurrentSlope) // and forward going up delay 500 call Walk(4) // 4 steps return
sub Walk(Num) gosub InitServoNames gosub StartWalk delay 1000 stepping _MODE for i=1 to Num call TakeStep(RGT) call TakeStep(LFT) next gosub StopWalk return
sub TakeStep(leg) FIGURE 3. Taking Steps call LegForward(leg) The difficult work is performed by the routine TakeStep call BodyForwardOverFoot(leg) which can perform either a right or left step. In either call LeanToCenter(leg) case, TakeStep assumes that the robot is already leaning call StartOpStepPosition(leg) appropriately, so that the stepping foot is off the ground. return The routine ends with the robot leaning in the opposite direction, so it’s prepared for the sub LegForward(leg) FIGURE 4. amount = _StepSize next step. The actual gosub InitServoNames step is accomplished call FromCurServoPos(leg+1,amount) by calling four delay 300 routines as shown call FromCurServoPos(leg+3,5) // raise toe slightly to prevent stubbing call FromCurServoPos(leg+2,-amount) in Figure 3. These if leg = RGT four routines will call BalanceWithArms(100-_DeltaXtilt,_DesiredYtilt) move the stepping else leg forward, bring call BalanceWithArms(100+_DeltaXtilt,_DesiredYtilt) the body forward endif delay 500 over the stepping call FromCurServoPos(leg+2,amount) foot, lean the robot call FromCurServoPos(leg+3,-amount-5) // lowers toe back to the center call BalanceWithArms(100,_DesiredYtilt) to regain a good return balance, and finally 12 SERVO Issue-1.2020 lean further so the robot is ready to step with the opposite leg. FIGURE 5. FIGURE 7. Moving the Leg Forward The routine LegForward is shown in Figure 4. It uses the leg value passed to it to access the different joints (+1 is the thigh, +2 is the knee, and +3 is the F/R ankle). In keeping with the philosophy discussed earlier, all joints are moved based on the current step size. Notice also that the toe is raised slightly at one point to help prevent it from stubbing (in case the robot is leaning forward as depicted by Figure 1), and then lowered again at the end of the routine. Notice also that the final line in this routine moves the arms to improve the robot’s balance. Executing this routine puts the robot in the position shown in Figure 5. Notice the knee and ankle joints are now in a straight line, extending the foot forward. sub BodyForwardOverFoot(leg) gosub InitServoNames FIGURE 6. Moving the Body SS = _StepSize if leg=RGT Forward call FromCurServoPos(Rknee,-SS#4) The routine in Figure 6 moves the call FromCurServoPos(Rankle,SS#4) robot’s body over the stepping leg. call FromCurServoPos(Lthigh,-SS#4) Because the robot is balanced on one call FromCurServoPos(Lknee,SS#4) foot while this is happening, the step- for i=1 to 4 sized movements are divided into smaller call FromCurServoPos(Rknee,-SS/4) actions and performed within a loop. call FromCurServoPos(Rankle,SS/4) The use of RobotBASIC’s modulo call FromCurServoPos(Lthigh,-SS/4) operator (#) and integer divide ensures call FromCurServoPos(Lknee,SS/4) that each movement is fully completed. call BalanceWithArms(100-_DeltaXtilt,_DesiredYtilt) next Notice that the arms are used to help elseif leg=LFT maintain balance as the movement call FromCurServoPos(Lknee,-SS#4) progresses. call FromCurServoPos(Lankle,SS#4) Figure 7 shows how the robot will call FromCurServoPos(Rthigh,-SS#4) appear after this routine is executed. This call FromCurServoPos(Rknee,SS#4) pose looks very much like Figure 5, but for i=1 to 4 the body is definitely forward. Compare call FromCurServoPos(Lknee,-SS/4) the knee and ankle joints in Figures 5 call FromCurServoPos(Lankle,SS/4) and 7. The camera angle makes these call FromCurServoPos(Rthigh,-SS/4) differences very easy to see. call FromCurServoPos(Rknee,SS/4) call BalanceWithArms(100+_DeltaXtilt,_DesiredYtilt) next Leaning Back to call Center endif At this point in the sequence, the return SERVO Issue-1.2020 13 sub LeanToCenter(leg) gosub InitServoNames FIGURE 8. if leg=RGT OpLeg = LFT else OpLeg = RGT endif call ShortenLegForStep(OpLeg,_PrimaryStepSize#4) delay 100 call Lean(leg,_LeanAngle#4) call BalanceWithArms(_DesiredXtilt,_DesiredYtilt) for i=1 to 4 call ShortenLegForStep(OpLeg,_PrimaryStepSize/4) delay 100 call Lean(leg,_LeanAngle/4) call BalanceWithArms(_DesiredXtilt,_DesiredYtilt) next delay 300 return FIGURE 9. robot is still leaning to one side, so it needs to move its weight back toward the stepping foot. Figure 8 shows how (lower) step when it’s going downward. this is accomplished. This adjustment to the step size means the stepping Basically, it shortens the leg the robot is currently foot will be approximately the same distance from the floor standing on in order to lower the stepping foot to the regardless of the terrain’s slope. This means we can always ground. You might think the amount of this lowering would lower the robot a proper amount by moving the joints in change if the robot is moving on an incline. The reason it the supporting leg by the _PrimaryStepSize initialized earlier doesn’t is because we have the robot taking a bigger (thus (this is the step size for level terrain). Figure 9 shows how higher) step when it’s walking up an incline and a smaller the robot will be positioned after this routine is executed. Notice the robot is sub StartOpStepPosition(leg) well balanced, but gosub InitServoNames the stepping foot if leg=RGT is forward in the FIGURE 10. OpLeg = LFT stance. else The action OpLeg = RGT of lowering the endif call Lean(leg,_LeanAngle/2) stepping leg to the call FromCtrServoPos(leg+2,0) // 0 forces startup angles ground is much call FromCtrServoPos(leg+1,-_CurrentSlope) // maintains body tilt for different than call FromCtrServoPos(OpLeg+1,-_CurrentSlope) // navigating a slope letting the robot’s call FromCtrServoPos(OpLeg+2,0) weight pull the call FromCtrServoPos(OpLeg+3,0) body forward onto call Lean(leg,_LeanAngle/2) that leg. // balance based on current lean direction if leg = LFT This action call BalanceWithArms(100-_DeltaXtilt,_DesiredYtilt) helps the robot else maintain its call BalanceWithArms(100+_DeltaXtilt,_DesiredYtilt) balance and is a endif vital move when delay 500 walking up and return down inclines. 14 SERVO Issue-1.2020 Preparing to FIGURE 11. Conclusion Step with the Programming hobby- Opposite Leg oriented walking robots can be both frustrating and rewarding. With the robot balanced on Experimenting with a variety of two feet again, the next action is movements can greatly improve for the robot to lean away from your understanding of the the leg that will make the next problems and ultimately help you step. Figure 10 shows how this is find innovative solutions. Here’s a accomplished. YouTube video demonstrating my In this routine, all the joints robot in action: https://youtu. are reset to their original balanced be/LB_uBJh5bQ8. position (as was established by Watching it actively balance StartWalk, except that the robot as it walks on different slopes may be leaning either left or should be exciting for anyone who right depending on which foot understands how difficult this is stepping). This always leaves project is. I’m sure that fine-tuning the robot ready to proceed with properties such as delays, motor the next step or to return to the speeds, and balancing algorithms normal standing position. could greatly improve the robot’s Figure 11 shows how the performance, but at least for now, robot is positioned after this such modifications will be left for routine is executed. the motivated reader. SV
SERVO Issue-1.2020 15 Goal Prediction Using AI
From this article, you’ll discover the basics of machine learning and the power of what machine learning can do. I’ll discuss the implementation of different machine learning algorithms for predicting a simple binary classifi cation. This article is mainly focused on beginners who are very new to machine learning. I’ll show you how to use different algorithms on predicting if a goal has been scored or not by Cristiano Ronaldo — the famous Portuguese professional footballer who plays as a forward for Serie A club Juventus and captains the Portugal national team. He is often considered the best player in the world and widely regarded as one of the greatest players of all time. 16 SERVO Issue-1.2020 To post comments on this article and find any associated files and/or By Rajat Keshri downloads, go to www.servomagazine.com/magazine/issue/2020/01.
To understand how these algorithms work, check the Introduction following links which offer great explanations and can help While watching any football (soccer) match, we want you to understand the workings of these algorithms: the team that we support to score a goal. We wait patiently until a player from our team gets close enough to the goal 1. Linear Regression: https://towardsdatascience.com/ and makes a shot ... which seems to be going into the goal linear-regression-detailed-view-ea73175f6e86 but misses, sadly. Can AI (Artificial Intelligence) predict and 2. Logistic Regression: https://towardsdatascience.com/ explain why that player missed the shot from that particular logistic-regression-detailed-overview-46c4da4303bc location using data analytics and machine learning? 3. Random Forest: https://towardsdatascience.com/ In this article, we’ll experiment with different ML random-forest-and-its-implementation-71824ced454f (machine learning) algorithms and teach an AI to predict if a 4. Neural Networks: https://towardsdatascience.com/ player will score a goal or not. first-neural-network-for-beginners-explained-with- Machine learning plays a key role in many different code-4cfd37e06eaf applications such as computer vision, data mining, natural language processing, speech recognition, and others. ML Let’s start with understanding the inner workings and provides potential solutions in all the above-mentioned the approach for our project of predicting if goals are scored domains and more. It’s surely going to be a driving force in or not. Before we start with any of the code, the first thing our future digital civilization. we should do is to go through the data set thoroughly. Here, we’ll see how we can use different machine We must understand the data set completely and try learning algorithms and build a simple binary classifier which to figure out the most important features from the data will classify whether a goal can be scored or not, based on set which we’ll be using for training our model. Sampling the given input data. This project was done as part of a and extracting wrong features might sometimes lead to hackathon I participated in and from which the dataset was inaccuracies in your model. provided. In the following section, we’ll go over some basic theory of different machine learning algorithms which we’ll be Prerequisites trying to code and apply in the later part of this article. The following packages will be used in the development of this project. Also, we’ll be using Python 3.6 here, but any Some Theory version above 3.6 should be fine to use. There are many machine learning algorithms present. 1. Sklearn: Machine learning library. In this project, we’ll be using classification algorithms since 2. Pandas: Library used for importing the csv files and we’ll be needing to predict whether a goal is scored or not. parsing the columns. This is also called binary classification. 3. Numpy: Library used for storing the training data in an If you have basic knowledge of different machine array. Numpy arrays are most widely used to store the learning algorithms and types of classification in machine training data and the sklearn library accepts the input learning, feel free to skip the theory section. data in the form of numpy arrays. Classification in machine learning is done in two ways: 4. If any of the libraries are not present in your system, supervised and unsupervised. Supervised learning involves just pip install that particular library. The guide to use the data set given with the output each data point should pip is at https://www.w3schools.com/python/ produce. The algorithm learns the patterns which produce a python_pip.asp. certain output and tries to generalize it with supervision. Supervised learning basically contains the output The following shows the code snippet with all the labels to be predicted in the data set, and learns how to libraries to be imported: predict those values by backtracking and generalization. Unsupervised learning trains on the data and tries to import pandas as pd import numpy as np generalize blindly without knowing what category each data import math point belongs to. It creates a pattern and generalizes the import scipy data points based on its features, and creates output labels from sklearn.preprocessing import LabelEncoder, OneHotEncoder for them during the training process. from sklearn.model_selection import train_test_ Here, we’ll be focusing only on the supervised split learning method. Some of these methods which we’ll be from sklearn.linear_model import LinearRegression from sklearn.model_selection import train_test_ experimenting with are linear regression, logistic regression, split random forest, and neural networks. from sklearn.datasets import load_boston SERVO Issue-1.2020 17 from sklearn.metrics import mean_squared_error csv file using pandas and define the columns which act as from scipy.stats import spearmanr from sklearn.ensemble import the input data and the columns which are the output labels RandomForestClassifier for training. from sklearn.preprocessing import scale Here, column 10 is the “is_goal” column which acts like from sklearn.linear_model import LogisticRegression the output label and 2,3,4,5,9 columns are the input labels from sklearn.model_selection import train_test_ location_x, location_y, remaining_sec, power_of_shot, and split distance_of_shot, respectively. If you want to try training from sklearn import preprocessing from sklearn import svm your model with other feature columns from the data.csv, from sklearn.ensemble import then just add those column numbers in the array. RandomForestClassifier from sklearn.neural_network import MLPClassifier datasets = pd.read_csv(‘data.csv’)output=pd. DataFrame(datasets) cols = [10] output = output[output.columns[cols]]df = Dataset Preprocessing pd.DataFrame(datasets) cols = [2,3,4,5,9] The data set used here is a csv file with information df = df[df.columns[cols]] about different matches played by Real Madrid against different teams. The data set contains different fields Once we have read the features from the csv files, describing the goal scored by Ronaldo at different situations we must go through and remove all the noise from these and scenarios, like what time was the goal scored, how columns. We loop through the features and check if a much distance from the goal, what was the shot power, particular value for that column if NAN or not. If it’s NAN, what angle did he score at, etc. As mentioned before, this we drop the entire row, removing the entire noisy data. data set was given to me during a hackathon, so I’m not Once the noisy data is removed, we store the entire 2D sure if it’s publicly available on Kaggle or any other website. array of multiple column features in variables X and Y: Either way, the data set is included in the article downloads or you can get it from https://github.com/rajatkeshri/ZS- #Removing rows with Output label not defined k=0 HACK-predict-ronaldo-goal. x=[] Figure 1 shows some of the columns for the data set. for i in df[“is_goal”]: From the data set, we’ll be using the following columns as if math.isnan(i): x.append(k) input data: location_x, location_y, power_of_shot, distance_ #print(i) of_shot, remaining_sec, and is_goal column as the output k+=1 label. You can use the other fields for training the model and df=(df.drop(x))#Removing rows with distance of shot not defined experimenting with it, but in this article, I’ll just explain the k=0 use of the input field data columns listed above. x=[] You’ll notice there are many fields which are empty and for i in df[“distance_of_shot”]: there’s a lot of noise in this data set. Our first step is to go if math.isnan(i): through the data set and fix the noisy data and remove all x.append(df.index[k]) the empty fields. #print(i) k+=1 Let’s jump to the code now. First, we open the data set df=(df.drop(x))#Removing rows with power of shot not defined k=0 Figure 1. Dataset in csv format.
18 SERVO Issue-1.2020 x=[] To train these models, we call “.fit” on these objects. For for i in df[“power_of_shot”]: more information on each of the machine learning algorithm if math.isnan(i): classes, refer to https://scikit-learn.org/stable. x.append(df.index[k]) #print(i) LR=LinearRegression() k+=1 Lr=LogisticRegression(random_state=0, df=(df.drop(x))#Removing rows with X axis solver=’lbfgs’, multi_class=’ovr’) location not defined k=0 RF = RandomForestClassifier(n_estimators=100, max_ depth=2, random_state=0) x=[] for i in df[“location_x”]: NN = MLPClassifier(solver=’lbfgs’, alpha=1e-5, if math.isnan(i): hidden_layer_sizes=(5, 2), random_state=1) x.append(df.index[k]) LR.fit(X_train,Y_train) #linear regression #print(i) Lr.fit(X_train,Y_train) #logistic regression k+=1 RF.fit(X_train, Y_train) #random forest df=(df.drop(x))#Removing rows with Y axis NN.fit(X_train, Y_train) #neural network multi- layer perception model location not defined k=0 x=[] Once the training is complete, we check how different for i in df[“location_y”]: models have performed. This can be done by calling the if math.isnan(i): x.append(df.index[k]) “.score” method. The .score method prints an accuracy on #print(i) how our model performs on the test data: k+=1 df=(df.drop(x)) print(LR.score(X_test,Y_test)) #print(df)#Removing rows with remaining time not print(Lr.score(X_test,Y_test)) defined print(RF.score(X_test,Y_test)) k=0 print(NN.score(X_test,Y_test)) x=[] for i in df[“remaining_sec”]: if math.isnan(i): Also, if we want to check the predictions on our test x.append(df.index[k]) data or give new data values and predict whether a goal is #print(i) k+=1 scored or not, we can do it by using the “.predict” method. df=(df.drop(x)) The output produced after the predict method is either #print(df)X = df.iloc[:, :-1].values 1 or 0, where 1 stands for “Yes, he scored a goal!” and 0 Y = df.iloc[:, 4].values stands for “Hard luck, he will definitely score next time.” Now we have our clean data set. The next step is to split the entire data into train and test data. This is done so loc_x = 10 loc_y = 12 that we train our model on the train data and then test it remaining_time = 20 for its accuracy and score on the test data. This will help us distance = 32 understand where our model stands in predictions and can power_of_shot = 3 custom_input=[[loc_x,loc_y,remaining_time,power_ thus help us in tweaking the model. of_shot,distance]]print(LR.predict(X_test)) To split into train and test data, we use the function print(Lr.predict(X_test)) train_test_split which is imported from the sklearn library. print(RF.predict(X_test)) print(NN.predict(X_test))print(Lr.predict(custom_ Random state basically means the percentage of data which input)) will be used as train and test data; 0.2 means 20%:
(X_train, X_test, Y_train, Y_test) = train_test_ split(X, Y, random_state=0.2) Results First of all, congratulations! We have successfully built a binary classification model AI which predicts whether Training Ronaldo can score a goal or not. We observed that it’s a Okay. We’ve finished understanding the data set and basic binary classification problem; the logistic regression also cleaned it with some pre-processing. The only step left performs the best with approximately 95% accuracy, but the is training the model. As mentioned earlier, we’ll be training other machine learning models perform and give a score our model using linear regression, logistic regression, of approximately 60–70% accuracy. This accuracy can be random forest regression, and neural network. These increased by adding more features to the training of the algorithms are available within the sklearn library directly model. and that is what we’ll be using. I hope you enjoyed this article. Cheers! SV First, we create objects of different machine learning algorithms and then pass our input features with output The entire project code is included in the article downloads and labels to them. These algorithms generalize upon the data can also be found at https://github.com/rajatkeshri/ZS-HACK- we feed them. predict-ronaldo-goal. SERVO Issue-1.2020 19 bots IN BRIEF
Armed and Dangerous? esearchers from Université de Sherbrooke Rin Canada have designed a waist-mounted, remote controlled hydraulic arm that can help you with all kinds of tasks. Oh, and you can smash through walls with it too. This type of wearable robotic arm is known as “supernumerary.” The system created by the Canadian researchers (in partnership with Exonetik) has three degrees of freedom and is actuated by magnetorheological clutches and hydrostatic transmissions with the goal of “mimicking the performance of a human arm in a multitude of industrial and domestic applications.” (Like wall punching.) The hydraulic system provides comparatively high power, but the power system itself is connected to the user through a tether, minimizing how much mass the user Researchers at the has to actually wear (and keeping the inertia of the arm low) while also limiting mobility somewhat. Université de Sherbrooke in Off-board power does put a bit of a dampener on the superhero potential, but in practical Canada developed a waist- terms, users aren’t likely to be moving around all that much. If they are, mobile options could include mounted hydraulic arm that being tethered to an autonomous vehicle that follows you around or perhaps a more portable can help you with all kinds backpack power unit. of tasks. The robotic arm itself weighs just over four kilograms — about the same as a real human arm. It can lift 5 kg and has a maximum end effector speed of 3.4 meters per second, with a workspace Photos courtesy of that’s restricted to keep it from smashing you into a wall. Université de Sherbrooke. At the moment, there isn’t much in the way of autonomy since the arm is being controlled by a second human via a miniature handheld arm in a master-slave configuration. The researchers suggest that adding some sensors could allow the arm to do things like pick vegetables next to the user, as well as do more collaborative tasks like providing tool assistance. You can think of it as being able to act as a co-worker, either directly increasing productivity by performing the same task as the user in parallel, or doing some different tasks in order to free up the user to do stuff that requires creativity or judgement.
The researchers envision a number of applications for their supernumerary arm, including: vegetable picking (a, b); painting a wall (c); washing a window (d); handing tools to a worker (e, f); and playing badminton (g).
20 SERVO Issue-1.2020 bots IN BRIEF
HAMR-Jr Time
he Harvard Ambulatory MicroRobot T(HAMR) was a bit chunky back in 2018, measuring about five centimeters long and weighing around three grams. However, a new version of HAMR has been introduced. Called HAMR-Jr, it’s significantly smaller at just a tenth of the weight and it comes up to about knee-high on a cockroach. HAMR-Jr may be tiny, but it’s no slouch. Piezoelectric actuators can drive it at nearly 14 body lengths (30 cm) per second, at a gait frequency of 200 Hz. The actuators can be cranked up even more approaching 300 Hz, but the robot actually slows down past 200 Hz because it turns out that 200 Hz hits a sort of resonant sweet spot that gives the About the size of a penny, HAMR-Jr is one of the smallest and robot as much leg lift and stride length as fastest insect-scale robots, capable of running at nearly 14 body possible. lengths (30 centimeters) per second. Photo courtesy of Kaushik Jayaram/University of Colorado Boulder/Harvard SEAS.
Slow as a SlothBot
e tend to focus on motion a lot with robots, Wand the most dynamic robots get the most attention. This isn’t to say that highly dynamic robots don’t deserve our attention, but there are other robotic philosophies that, while perhaps less visually exciting, are equally valuable under the right circumstances. Magnus Egerstedt, a robotics professor at Georgia Tech, was inspired by some sloths he met in Costa Rica to explore the idea of “slowness as a design paradigm” through an arboreal robot called SlothBot. Since the robot moves so slowly, why use a robot at all you ask. It may be very energy-efficient, but it’s definitely not more energy efficient than a Georgia Tech roboticists static sensing system that’s just bolted to a tree for example. The robot moves but it’s also going to be are exploring the idea much more expensive (and likely much less reliable) than a handful of static sensors that could cover of “slowness as a design a similar area. The problem with static sensors, though, is that they’re constrained by power availability, paradigm” through an and in environments like under a dense tree canopy, you’re not going to be able to augment their arboreal robot called lifetime with solar panels. SlothBot. If your goal is a long duration study of a small area (over weeks or months or more), SlothBot Photo courtesy of is uniquely useful in this context because it can crawl out from beneath a tree to find some sun to Georgia Tech. recharge itself, then crawl right back again to resume collecting data. SERVO Issue-1.2020 21 Healthcare Gone to the Dogs
ome coronavirus patients at SBrigham and Women’s Hospital in Boston are being greeted by a new kind of nurse: a four-legged robot named “Spot.” Boston Dynamics’ famed dog- like robot has been working with patients at the hospital to provide a buffer between potentially contagious cases and swamped health care officials. “It’s kind of fun working with it,” Dr. Peter Chai recently told Digital Trends. “[Spot] is not that hard to control, and it gets us to where we need to be without being exposed.” The robot — which is best known for a series of viral videos showing its ability to walk, jump, and even dance on four legs — has been lending a helping hand (leg?), according to authorities at the hospital and Boston Dynamics. “Our hope is that these tools can enable developers and roboticists to rapidly deploy robots in order to reduce risks to medical staff,” Boston Dynamics wrote in a recent blog post announcing the collaboration. Chai said Spot is being used in the hospital’s outdoor triage tent for patients who have upper respiratory symptoms but are not sick enough to stay in the hospital. Spot greets patients with an iPad-like device that allows them to see and talk to a physician virtually.
Cheetahs Never Prosper
he North Carolina State cheetah robot T— called LEAP, or Leveraging Elastic instabilities for Amplified Performance — is a soft robot that can significantly outpace other soft robots by borrowing inspiration from the ways real cheetahs flex their spines to achieve speed and power. By making the soft robot’s flexible spine able to quickly flex and extend to mimic the active role of a cheetah’s spine, Photo courtesy of Jie Yan/North Carolina State University. it’s possible to quickly propel the soft robot forward on the ground (and even underwater).
22 SERVO Issue-1.2020 Bot or Not?
or the past several years, there’s been heightened Fconcern about the impact of so-called bots on platforms like Twitter. A bot in this context is a fake account synonymous with helping to spread fake news or misinformation online. So, how exactly do you tell the difference between an actual human user and a bot? While clues such as the use of the basic default “egg” avatar by Twitter, a username consisting of long strings of numbers, and a penchant for tweeting about certain topics might provide a few pointers. However, that’s hardly conclusive evidence. That’s the challenge a recent project from a pair of researchers at the University of Southern California and University of London set out to solve. They have created an AI that’s designed to sort fake Twitter accounts from the real ones based on their patterns of online behavior. “Detecting bots can be very challenging as they continuously evolve and become more sophisticated,” Emilio Ferrara, research assistant professor in the USC Department of Computer Science, told Digital Trends recently. “Existing tools that work well with older and simpler types of bots are not as accurate to predict more complex ones. So, it’s always exciting to identify new, previously unknown characteristics of the behavior of human users that are not yet exhibited by bots. This could [be used to help] improve the accuracy of detection tools.” The researchers leveraged various datasets of hand-labeled examples of both fake and real Twitter account messages produced by other researchers in the community. In total, they trained their system on 8.4 million tweets from 3,500 human accounts and an additional 3.4 million tweets from 5,000 bots. This helped them to uncover a variety of insights into tweeting patterns. For instance, human users are up to five times more likely to reply to messages. They also get increasingly interactive with other users over the course of a long Twitter session, while the length of an average tweet decreases during this same time frame. Bots, on the other hand, show no such changes.
Do the Worm
eneral Electric is getting into giant robot Gearthworms.While this might sound unlikely, GE’s research division has landed a big $2.5 million award from the Defense Advanced Research Projects Agency (DARPA) to ensure the project continues crawling along. “What makes this so unique is that we’re really drawing inspiration from two sources in nature: the earthworm and tree roots,” Deepak Trivedi, who is leading this project for GE Research, recently told Digital Trends. “From the earthworm, we’re mimicking its fast rhythmic movements to rapidly and efficiently form the tunnels we’re trying to form. And from the tree roots, we’re mimicking [their] scale and ability to create large force by studying how roots grow into the ground. It’s the combination of these two forces of nature that makes our project — and robot — so unique.” The soft robot tunneler is made up of large segmented pieces which act like the fluid-filled “hydrostatic skeleton” found in invertebrates. The robot’s artificial muscles move like a real earthworm’s in order to propel it forward, while the segmented design also gives it impressive freedom of movement and the ability to maneuver into difficult-to-reach places.
SERVO Issue-1.2020 23 Draganfly Drones Do Monitoring n a rush to combat the global spread of the deadly Icoronavirus (COVID-19), Draganfly will deploy “pandemic drones” to remotely monitor and detect people with infectious and respiratory conditions to help stop the spread of the disease. The Draganfly drones will be fitted with a specialized sensor and computer vision system that can monitor temperature, heart and respiratory rates, as well as detect people sneezing and coughing in crowds and other places where groups of people may work or congregate. Draganfly will serve as the global systems integrator for the Vital Intelligence Project: a health and respiratory The Draganflyer monitoring platform from Vital Intelligence, Inc. The breakthrough technology was developed in a Commander UAV is collaboration between the University of South Australia and the Science and Technology Group a remotely operated (DST), which is part of Australia’s Defence Department. The project has an initial budget of $1.5 miniature helicopter million. designed to carry wireless The sensing system uses existing and new camera networks, UAVs, and remotely piloted aircraft camera systems. systems for health monitoring and detection of infectious and respiratory conditions, including Photo courtesy of monitoring temperatures, heart rates, and respiratory rates. Draganfly. The drones can monitor people in public crowds, workforces, airlines, cruise ships, convention centers, border crossings, or critical infrastructure facilities. The technology can also be used to monitor potential at-risk groups, such as seniors in care facilities.
Follow the Bouncing Ball
-Kuhn over at Electron Dust started thinking about Tball juggling machines in 2015. He wrote about his first attempts at creating them in the Electron Dust blog post in 2017. He then wrote another post about his then newest build in 2018. Now, in 2020, the quest to get a machine to juggle a ping pong ball reliably has come to an end (as this current build is able to keep the ball bouncing for hours.) The machine requires the following components to work:
• 1x Teensy 4.0 microcontroller running the code at https://github.com/T-Kuhn/ HighPrecisionStepperJuggler/tree/master/ Arduino/HighPrecisionStepperJuggler • 4x StepperOnline DM442S stepper motor drivers • 4x Nema 17 stepper motors with 5:1 planetary gearbox • 1x 48V 8A power supply • 1x e-con Systems See3CAM_CU135 camera • 1x Windows computer with OpenCV installed on it • All the parts defined in the Fusion360 project described at https://github.com/T-Kuhn/ HighPrecisionStepperJuggler/tree/master/Autodesk%20Fusion360%20data • The custom Windows Application (made with Unity) described at https://github.com/T-Kuhn/ HighPrecisionStepperJuggler/tree/master/Unity/HighPrecisionStepperJuggler/Build
You can watch it bounce here: https://electrondust.com/2020/03/01/the-octo-bouncer.
24 SERVO Issue-1.2020 Gonna Burst Your Bubble
hile folks around the world are working on different artificial Wpollination systems, there’s really no replacing the productivity, efficiency, and genius of bees. However, researchers at the Japan Advanced Institute of Science and Technology (JAIST) have come up with an alternate method of pollination: pollen-infused soap bubbles blown out of a bubble maker mounted to a drone. And it apparently works really well. Most other examples of robotic pollination have involved direct contact between a pollen-carrying robot and a flower. This works, but is not really efficient since it requires the robot to do what bees do: identify and localize individual flowers and then interact with them one at a time for reliable pollination. The problem becomes scaling to cover an entire orchard. In a recent issue of iScience, JAIST researcher Eijiro Miyako described how his team had been working on a small pollinating drone that had the unfortunate side-effect of frequently destroying the flowers that it came in contact with. Frustrated, Miyako needed to find a better pollination technique. While blowing bubbles at a park with his son, Miyako realized that if those bubbles could carry pollen grains, they’d make an ideal delivery system. Researchers in Japan developed a drone You can create and transport bubbles very efficiently, generate them easily, equipped with a bubble maker for and they literally disappear after delivering their payload. They’re not targetable, autonomous pollination. of course, but it’s not like they need to chase anything, and there’s absolutely no reason to not compensate for low accuracy with high volume. Photos courtesy of iScience. According to Miyako:
We accidentally found that natural pollen grains can be easily incorporated into a soap film and flown in the air using various bubble devices.
To show that their bubble pollination approach is scalable, the researchers equipped a drone with a bubble machine capable of generating 5,000 bubbles per minute. In one experiment, the method resulted in an overall success rate of 90 percent when the drone moved over flowers at 2 m/s at a height of 2 m.
SERVO Issue-1.2020 25 NEW PRODUCTS
36 Tooth Pinion Gear with an 80 tooth hub gear spaced 48 mm away for a 2:1 ratio, or it can mate to a 20 tooth gear to create a very compact 2:1 ratio only 24 mm apart. If your build is able to adjust the spacing between your gears, it’s able to mesh to any MOD 0.8 gear you choose. The counterbore on the top side of this gear allows you to run right up against an 8 mm bearing without the use of a shim as well. Price is also $8.99. he 36 tooth 8 mm REX bore 30 Tooth Miter Gear Tpinion gear is now available from goBILDA. The bore perfectly matches perfectly match 6 mm D-shafting, as their 8 mm REX shafting to create a well as the D-shafts used on goBILDA’s positive drive. While little work is left 5202 Series Gear Motors. The steel for the set screws, goBILDA put two of construction provides excellent them in for good measure. strength and wear resistance. Price is This particular gear is able to be $7.99. meshed with an 84 tooth hub gear spaced 48 mm away for a 2.33:1 ratio, 8 mm Pitch Steel Set or it can mate to a 24 tooth gear to create a very compact 1.5:1 ratio only Screw Sprocket 24 mm apart. If your build provides he 8 mm REX Bore Miter Gear from the freedom to adjust the spacing TgoBILDA is able to mate with any between your gears, it’s able to mesh other 2315 Series Miter Gear. A miter to any MOD 0.8 gear that suits your gear is a specific type of bevel gear. needs. The counterbore on the top Two mating miter gears create a side of the gear allows you to run right 1:1 ratio, and transmit power at a 90 up against an 8 mm bearing without degree angle due to the 45 degree the use of a shim. Price is $8.99. pitch cone angle. The underneath side of this gear 40 Tooth Pinion Gear has been dished out to allow a thrust bearing to set the location of the gear (relative to the inside wall of an 1120 Series U-Channel) and counteract the potential spreading forces in the most extreme applications. Additionally, the 32 mm shelf on his 10 tooth sprocket from the back will allow a 32 mm diameter TgoBILDA has an 8 mm REX bore component such as goRAIL, goTUBE, to perfectly match their 8 mm REX or a Sonic Hub to nest down in the shafting. Its steel construction also cavity and fasten with M4 socket head provides excellent strength and wear screws. Price is $12.99. resistance. Price is $7.99 as well. he 40 tooth 8 mm REX bore pinion For further information, contact: Tgear is also now available from 38 mm Pitch Steel Set goBILDA and perfectly matches the 8 goBILDA mm REX shafting to create a positive Screw Sprocket www.gobilda.com drive as well. There are two set screws. his 10 tooth sprocket from This gear is able to be meshed TgoBILDA has a 6 mm D-bore to 26 SERVO Issue-1.2020 Learning Platform for Arduino hands-on projects. Designed with the experienced user in mind, the Explorer edition helps you build and test your electronic concepts quickly. It’s jam-packed with powerful features, which include:
• 128x64 line character and graphics OLED • Power options • Bluetooth LE • Prototyping area • Eight channel addressable LEDs • Mini breadboard • And more ... r. Duino has expanded its line of rapid learning and Dprototyping platforms with its latest Explorer edition and The Pioneer is Arduino Uno compatible, while the an updated Pioneer version. Explorer is compatible with the Uno and Nano versions. Building and tinkering with electronics is much easier Expansion packs are also available for both the Pioneer with these Arduino compatible shields. They are complete and Explorer. Both platforms are currently on sale. compact learning and prototyping systems which are perfect For further information, contact: for anyone interested in electronics. Designed with the beginner in mind, the Pioneer Edition Dr. Duino helps you easily learn about the world of electronics through www.drduino.com
Programmable USB Keyboard Controller Module aelig Company, Inc., has introduced the SKeyWarrior28: the smallest controller of the KeyWarrior family with a great deal of functionality that is more than just standard keyboard functions. The KeyWarrior28 — available as a 3.3V QFN28 chip or DIL28 module — controls up to 64 keys in an 8x8 matrix. Just a USB cable and the keys are connected to the module. The functionality of the keys is programmable via a USB port and stored drivers and does not require special software. Each unit has in internal Flash memory. For instance, it can offer a key- a unique serial number and a built-in counter to register the operated mouse function or media and application controls number of erase cycles. KeyWarrior modules and ICs are like Play, Pause, Mute, Start Browser, etc. designed by Code Mercenaries. Pricing starts from $12.20. Each individual key can be programmed with either For further information, contact: a single key code, a key code plus a modifier (shift, ctrl, alt, gui), a macro, a mouse function, a media/application Saelig Company control, or an FN key. The two optional FN keys give the www.saelig.com ability to switch to a second or third key layout. Like the modifier keys, FN keys can be programmed to act as ‘locking’ or ‘sticky’ (locking, but only for the next key). Waterproof Smart Servos This allows mode switching or single finger operation. Each of the 19 macros can be programmed on to any of the DYNAMIXEL XW series of smart servos are the keys. A maximum of 31 key codes can be in each macro. TROBOTIS`first line of IP level models, featuring a certified There are three different types of macros. A static macro IP68 rating which means they’re good at one meter for a acts as if all keys in the macro are pressed at the same 24 hour duration. The servos are designed for use in wet time. Typing macros activate each code just momentarily. environments, underwater, and any outdoor applications This allows repeating characters, special character use, and where a sealed servo is necessary. The XW series come with upper/lower case in the macro. Cell macros work like the a separate waterproof cable and extension cable. text input on phones with numeric keypads. Pressing the Features include: key again removes the last character and replaces it with the next. The KeyWarrior28 works with existing system Continued on page 72 SERVO Issue-1.2020 27 Building a Better Box By Ryan Clingman
hen I started my journey into building combat robots, I followed a guide Wpublished in the Combat Zone section in one of the 2010 issues of SERVO to build an easy test box out of a steamer trunk. This test box has served me faithfully for a few years now. However, it could only be used for basic drive testing or static weapon testing. There just wasn’t enough room to really drive around with a Corner bracket installed on the end of a cut board. weapon running. As my experience as a builder grew, so did the destructive power to be easily stored without sheets to contain the power of the of my creations, until the little box disassembly. spinning weapons. couldn’t be relied on to contain them 3. I wanted it to be able to contain without signifi cant modifi cation. my bots if they smack the wall Construction It was time to build a bigger, with the weapon running at full better box. I had four goals I wanted speed. 1. Cut the boards into eight 47.25” to meet with my new box design: 4. I wanted it to be dead simple to lengths. source and build. 2. Pre-drill and screw the corner 1. I wanted it to be big enough to brackets onto one end of each drive around. The materials used include board. 2. I wanted it to be small enough (https://pastebin.com/ZRVeNz9K): 3. Pre-drill and screw four of the boards together to make two 4’ • 4x 1”x6”x8’ lumber square boxes. • 2x 24”x48” MDF sheets 4. Lay the polycarbonate on top of FEAFEATUREDTURED • 1x 48”x48”x1/4” one of the boxes, then pre-drill polycarbonate sheet and screw it to the top of the box, THISTHIS MONTHMONTH • 8x 6”x24” sheet metal strips with the screws 12” apart at most. • 8x corner brackets 5. Lay the two sheets of MDF on top 28 Building a Better • 2x utility hinges of the other box (soon to be the • 2x latches bottom), and drill and screw them Box • 1x handle to the box like the polycarbonate. • 120x #8x3/4” screws Then, fl ip the box over. 30 Stepping Stones — 6. Drill two holes near each end of The StorStoryy of Thunder With the exception of the all eight sheet metal strips; close polycarbonate sheet, all the supplies enough to be screwed to one of Child could be obtained with a trip to my the bottom boards. local hardware store. 7. Pre-drill and screw all eight sheet 33 Bringing About the The entire set of materials costs metal strips to the inside of the less than $300, with 70% of that cost MDF-fl oored box, with two strips Apocalypse being for the polycarbonate and metal overlapped to fi ll each side.
28 SERVO Issue-1.2020 To post comments on these articles and find any associated files and/or downloads, go to www.servomagazine.com/ magazine/issue/2020/01.
8. Lay the top box on top of the bottom box. 9. Mount the hinges on the back side where the two boxes meet, 12” from the ends. 10. Mount the latches on the front side where the two boxes meet, 12” from the ends. 11. Mount the handle in the middle of the front side of the box.
Congratulations! You’ve created a simple and sturdy test box that only required cutting a few boards to length and screwing it all together! The steel reinforced corners and inner frame combined with the 1/4” polycarbonate should make this test box strong enough to survive rigorous Boards assembled to form a box. testing up to the Beetleweight class. The inside is over 7” tall, which should accommodate the majority of Beetleweight designs, and the floor space is enough that it could even be used as an arena for 150g bots. Happy testing! SV
Completed steel-reinforced test box.
SERVO Issue-1.2020 29 Stepping Stones — The StorStoryy of Thunder
Child By Nate Franklin
fter my first event in late After getting all the necessary Despite this issue, Thunder Child 2012, I decided to get electronics and hardware, my dad managed to finish with a 1-2 record, started in the world of and I assembled it on the dining room and won a grudge match held during Beetleweight combat table a week before its first event: downtime. Arobots. Since I had no Motorama 2013. The bot was named After the event, I was given a lot fabrication skills or access to any Thunder Child, which came from the of advice from fellow builders. Thunder tools, one of my friends suggested I fictional ironclad warship in H.G. Wells’ Child would go on to compete at a purchase a kit from kitbots.com. War of the Worlds. few events over the next two years After looking at their selection, I The bot didn’t do so well. The where it achieved minimal success, chose the chassis for a four-wheel brick ESCs I purchased were too big for the usually getting knocked out of the based on the Beetleweight Trilobite as bot and drew way too much current, tournament with a single win. my introduction into the class. which resulted in most of my bot’s The turning point for Thunder motors burning Child came in summer 2015, when out throughout another builder that lived 30 minutes the competition. from me offered to help me out by
The new wedge didn’t last long, but it was a step Thunder Child at its first event. in the right direction.
30 SERVO Issue-1.2020 First place and best driver at Bot Blast 2016 with the D2 wedge. making a steel wedge for Thunder Child. With the kit’s CAD files freely available for reference, he was able to design a new attachment and taught me how to make it. It was my first real experience working with tools, but the wedge turned out nicely. The work paid off, and Thunder Child placed third at Bot Blast 2015, with the wedge coming in handy when dealing with horizontal spinners. Unfortunately, Thunder Child would struggle in the next two events, resulting in the wedge I had built getting destroyed by a nasty vertical spinner. In 2016, Thunder Child found success when Pete Smith (the owner of Kitbots) sold me a wedge from the BotKits D2 kits modified to fit Thunder Child. I managed to pull off an undefeated run at Bot Blast, and place second at SWORD later that year. The wedge worked extremely well against horizontal spinners but was an Original titanium axle and shaft collars (top) and new grade 8 bolt easy target for the new meta: vertical and lock nut (bottom). spinners with wedglets. I found the solution to the problem when BotKits released their Wolverine claws in 2017: S7 tool steel wedglets designed for fighting vertical spinners and other wedges. After finding out that the claws used the same size hole for the mounting that the Trilobite kits use, I instantly purchased a pair. With Thunder Child now able to swap to different attachments depending on the opponent, I chose to replace the stock titanium axle with shaft collars with a grade 8 hex bolt and lock nut. This allowed for easier attachment swapping since I didn’t need to worry about applying Loctite to any set screws. However, it came at the cost
The anti-D2 wheels (only used once) and wedglets.
SERVO Issue-1.2020 31 After solving the electrical gremlins, Thunder Child came back stronger than ever, placing at the next two events and fi nishing in fourth place at Motorama. I then took the bot overseas to the UK Beetleweight web series, “Bugglebots,” where it placed second in a fi eld of 30 bots from around the world and became a fan favorite. The only change in 2019 was swapping to the faster 22 millimeter motors and a brand new Futaba transmitter. These upgrades resulted in Thunder Child placing fi rst twice, much to my delight. Fighting Claws 2 at Bugglebots. After placing seventh at Motorama 2020, I felt it was time for a change. I took all the skills I of an additional ounce in weight. with the three attachments (wedge, had learned in CAD and built a new Thunder Child entered 2018 by claws, and wedglets), and proved Thunder Child from scratch. My placing fi fth at Motorama, stopped to be a huge learning experience. I original kit had done its job. It served only by a broken soldering joint. Things lost my fi rst match with the anti-D2 as a stepping stone into the world of were looking up, as I had also started confi guration, where one of the set designing combat robots. SV learning computer-aided design (CAD). screws came loose and a wheel fell My fi rst big project for Thunder off. Child was creating a set of wedglets In addition, the bot shut off at the designed to fi ght D2 kits, which had end of the fi ght, likely due to the new become increasingly popular in the speed controllers drawing too much Northeast. In addition, I came up with current like what happened at its fi rst an anti-D2 confi guration, where I could event. Despite this, I managed to fi ght swap Thunder Child’s normal snap through the loser’s bracket, utilizing all hubs for longer hubs that would fi t an three of the attachments to place third additional wheel for extra traction. after experiencing similar electronics Bot Blast 2018 was my fi rst event failures.
A render of the new Thunder Child. Coming soon to an arena near you!
32 SERVO Issue-1.2020 Bringing About the
Apocalypse By Ryan Clingman
ortable Apocalypse is my current bot in the Portable 3 lb category, and it’s Apocalypse an undercutter with a version 0, with a Ppowerful single tooth 3D printed frame. disk. The bot has gone through four major iterations, with each new version seeking to improve on the performance and shortcomings of the previous versions. Version 0 of the design began as a scaling-up of my 3D printed 1 lb bot design, Someone Else’s Problem. This meant that I 3D printed the frame as a solid chunk of glass-filled nylon, and then supplemented with UHMW plastic for armor to protect the wheels. Unfortunately, life happened, and it never saw competition. While I was waiting for the opportunity to make it to another competition, I slowly put together the design for Version 1 of Portable Apocalypse. The overall shape remained the same, but my discovery of metal laser and waterjet cutting services inspired me to make the frame out of metal instead; 2 mm titanium works great for the wedges for the popular D2 kits, so why not make your bot out of that? The main structure of the whole bot comes from its top and bottom plates. Aluminum standoffs between the plates provide the rest of the structure, and the standoffs can be press-fit into 3D printed walls to contain the electronics, as well as giving something to mount the motors and armor to. Due to the space constraints inherent in making an undercutter, Portable Apocalypse there weren’t a lot of parts that were version 1, featuring a titanium frame. ideal for dealing with both axial and radial forces in a small package.
SERVO Issue-1.2020 33 I can really tighten the shoulder bolt shaft down hard to lock the inner races of the bearings together and make the frame nice and tight, while still leaving the outer races and the weapon disk free to spin. Slots in the 3D printed pulley let me put in square nuts to clamp the pulley to the disk. After some issues I had with the weapon of the earlier versions of my 1 lb bot flexing enough to damage its own pulley, I designed it so that the disc is always directly over the weapon motor and pulley. This way, even if the weapon flexes, it just rubs on the pulley instead of having the chance to bite into the The two metal plates combined with some standoffs form the key pulley and risk disabling itself. part of the frame. I designed all this so that (with the exception of the weapon shaft and So, I wound up making my a bearing in both the disk and the power switch) I would only need one own unique bearing setup. There’s pulley, with a nested pair of washers size of hex wrench to fully assemble/ squeezed between disassemble the entire bot. them to help All the 6-32 screws for the frame handle axial loads use a 5/64” hex drive, and all the on the weapon metric screws for the motors need a disk. 2 mm hex drive, but the two are so
3D printed walls combine with the standoffs The weapon shaft setup allows the center of the to complete the electronics compartment and bearings to be clamped to the frame while leaving provide mounting points for the motors and the outer part free to spin with the disk and pulley. armor.
34 SERVO Issue-1.2020 The disk is designed to always be over the weapon motor to avoid having it deflect into the side of the pulley and damage it.
In Version 2 onward, square nuts pressed into the close together that I can use one hex battery in and printed walls provide all the horizontal attachment wrench for all of it. out. To alleviate points for the frame. Portable Apocalypse v1 performed this, the height fairly well at the NERC Franklin and length of Institute 2019 event at least in terms the electronics compartment were attach the wheel guards and drive of offense and durability, but the increased slightly to provide much motors to the frame. competition also served to highlight needed space for wire routing. After seeing the apparent success several points in the design that could Version 1 of the design used of the technique in the EndBots be improved on. a combination of heat-set inserts, Vector kits, I decided to change to Portable Apocalypse v2 may look nutstrip, and Actobotics parts to using square nuts press-fit into the much the same on the outside, but every part on the inside got changed out. I learned that having to completely remove the top plate to get the battery out for charging was more annoying than anticipated, so I made the lid for the electronics compartment its own separate part. Not needing to completely remove the top plate also means that the weapon motor can simply be mounted directly to the top plate instead of needing to find a funky way to mount it off the bottom plate. The other problem with the electronics compartment of version 1 was that I apparently failed to leave enough room for all the wires, leaving me to play a rousing game of spaghetti Tetris every time I took the
Portable Apocalypse Version 2, with aluminum frame for a less expensive option.
SERVO Issue-1.2020 35 Chinese brushed ESCs. All of it performed admirably. After a respectable showing at NERC’s Motorama 2020 event, I have now built Portable Apocalypse v3 with the goal of achieving a spot on the podium the next time around (no small feat when the competitions I frequent have 30-60 competitors to overcome to get there). With the v2 design working well, the changes were relatively minor this time. While the aluminum frame worked great, I have switched back to a titanium frame for the best durability. What lost me both matches and knocked me out of the previous tournament was my receiver slowly failing due to repeated impacts. Wrapping all the electronics in foam should help to abate the impacts and increase the lifespan of the parts. Portable Apocalypse Version 3 — back to titanium and better Bringing Portable Apocalypse than ever. to this point has been a measured process of evolution in the design, 3D printed parts to attach these parts the parts where I could. addressing fl aws in the design as well instead. The titanium frame plates were as looking at the building techniques At the time of building, I had replaced with thicker aluminum ones; that have worked well for others some inklings of trying to turn the the DIY brushless gear motors were and, incorporating them into my own design into a kit to sell, so I also tried replaced with off-the-shelf brushed designs. to reduce the cost and complexity of motors; and I tried out some cheap Only time will tell if it will come out on the top of the pile, but I plan to keep improving it until it gets there! SV Make Precision Metal Projects
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36 SERVO Issue-1.2020 GearBox THE MOST COMPLETE PROGRAMMING TUTORIAL! Everything you need to learn the fundamental concepts of PIC® microcontroller programming, including: •Program Flow •Device-To-Device Communication •Loops •User Interface Design •Coding Techniques •In-circuit Debugging •Binary Manipulation •And More! Includes all the necessary software, compiler, trainer $99.99 board, cable, tutorial with exercises and sample code! Check out our other popular products for PIC® developers including: U2 Programmer•PBP3 Compiler Prototyping Boards•Experimenter Boards Contact us at [email protected]
Get Your Robot Ru in’!
SERVO Issue-1.2020 37 38 SERVO Issue-1.2020 Meet Bot Ross
By Sam DiPietro, Brett Sawka, and Rohan Shah
Between the three of us, as engineering students, drawing just isn’t something we’re any good at. Fortunately, we are good at engineering. So, by extension, being good at engineering means we’re actually great at drawing. That is, after we build a robot to draw things for us! Enter Bot Ross: the ever-precise robot built to draw any picture your heart desires (as long as you can fi nd a version of that picture with a quick Google image search, of course).
ot Ross is an easy-to-use machine capable of on the PCB. This board ran the C code we wrote to operate turning an image from your computer into the stepper motors and drawing algorithm. an accurate sketch. Driven by a PIC32MX Responsible for Bot Ross’s entire range of motion, the Bmicrocontroller, two H-bridge circuits for motors needed to be precise and accurate — much like controlling stepper motors, and a serial the arms of his namesake. We decided to go with stepper communication interface with a Python script run on any motors as they offered not only accuracy but also range of computer, you can see Bot Ross come to life. motion. It draws with a pen attached to a servomotor controlled Stepper motors are a special kind of motor, containing rack and pinion mechanism to move the pen up and down, tiny “steps” that you can power. This means that the motor which moves in two dimensions using stepper motors which is essentially quantized into small, precise values which are turn threaded rods. easy to program. When you apply a voltage to each of the With a careful control algorithm, a linear interpolation “steps” — controlled by two coils of wire called inductors — of the desired image can be drawn in roughly 10 minutes. the gear on the inside aligns, turning the motor by a small It works with any image you upload to the system, meaning degree. By applying specifi c patterns to the motor, Bot Ross infi nite masterpieces await. would be able to precisely move to any location on the paper. Electronics Much like a human bicep that is bigger than the forearm, we used two different sized motors so that one To give Bot Ross the ability to think, we needed to add a motor could support the weight of the other. Just like the brain. While there are many different options for control, we bicep, the big motor would not only have to move up and decided to go with a PIC series microcontroller which would down the page, it would also have to carry around Bot give us all the computing power we’d need to draw and Ross’s “hand” which held the other stepper motor and the store images. pen. The PIC is a fi ne microcontroller, but we needed to fi rst Stepper motors (while very accurate) take a lot of power install it onto a printed circuit board (PCB) where it could to operate — too much for our microcontroller to directly receive power, distribute signals, and connect to a laptop. supply. The good news is, our microcontroller doesn’t have On the PCB, we added a port expander, which gave to actually do the heavy lifting. It just has to act as the the PIC an extra 12 input/output pins; a color LCD display operator. so that we could debug our programs; and fi nally, a low Using H-bridges, we can control the fl ow of current current power supply to give power to just the components through each of the motor coils that act as electromagnets. SERVO Issue-1.2020 39 By alternating the direction of current fl ow in each coil, the electromagnet can be activated in such a manner that the shaft rotates in discrete amounts. The current direction in each coil also dictates whether the motor turns
Figure 1: H-bridge current fl ow.
Figure 2: Schematic of main board.
40 SERVO Issue-1.2020 Figure 3: Schematic of stepper drivers. clockwise or counter-clockwise. This is shown in Figure 1. A full schematic of the system is shown in Figures 2 and 3. Coding It Up The software side of Bot Ross comes in three parts, each of which work together to drive the entire system. We have our motor control code, which is needed to work with our circuitry to get the steppers moving and our servo to lift the pen up and put it down. With that established, we needed a script to process images, formatting image data in a way that works well with our motor controlling code. This script also includes our method of communicating that image data from a computer to our PIC32MX microcontroller. Finally, the most visible part of our code comes with the control algorithm, which interfaces the data sent over by our image processing script with our motor control code. When it all comes together, we have everything we need to This chunk of code — called an interrupt service routine get Bot Ross to draw some pictures. (ISR) — would fl ip pins on or off to create the pulse form When starting to code, we fi gured the best place to above. If we were to let the ISR do this every single time it begin was with getting our motors moving, since a robot was triggered, that would mean the attached motor would that can’t move wouldn’t do a whole lot. With our motor always be moving in the same direction. We needed a way controller circuitry already built, we dug into determining the to change direction, and only move when we wanted to. right inputs to that circuitry to accomplish three main things: We accomplished both these things by setting up some spin a motor at the right time; turn it the exact right number global control variables for controlling our two motors. of degrees; and get it to spin in the direction we wanted. This gave the ISR a way to check whether the user (or the To make stepper motors move, they require two picture-drawing program) actually wanted the motor to carefully timed pulse pairs coming from our microcontroller move. Figuring out the direction worked similarly. to the H-bridge inputs. A “pair” of pulses in this case involves We could tell the ISR whether the motor should spin two pulses which are exactly opposite each other; meaning clockwise or counter-clockwise, and it checks every time. If when one pulse is on, the other is off, and vice versa. the direction variable is a 1, the motor spins clockwise with We needed to generate two of these pairs, one of the ISR-generated pulses shown above. If it’s a 0, the ISR which was offset from the other by exactly half the length uses the below waveforms to make the motor spin counter- of a pulse. This is best described using a diagram like the clockwise. one in Figure 4. Since timing is key, the best way to generate these pulses was to use one of the PIC32MX’s periodic interrupt timers. We can load the hardware timer with some value (corresponding to an amount of time), and it counts down to zero while other code runs on the CPU. Once the timer reaches zero, it interrupts whatever code is currently running in order to do something else. In our case, that “something else” was to turn on or off the GPIO pin used to send out pulses. Figure 4: Stepper motor control signal waveforms. SERVO Issue-1.2020 41 Figure 5: Physical design block outline (right) and construction (left).
With that 2D map of the image’s edges, we wrote an algorithm suitable for Bot Ross to draw the image as effi ciently as possible. The algorithm starts at the top right of the X-Y map and fi nds the fi rst coordinate where an edge actually is. The stepper motors turn on, move the pen to the right point, and place it down on the paper. Next, Bot Ross looks for any adjacent points which need to be drawn. If there is one, the pen moves there, drawing the fi rst little bit of the picture. Then, the algorithm looks for points adjacent to that point. This process continues until it fi nds an “end” point with nothing adjacent to it. When that happens, the pen goes up and it retraces its steps, fi nding any points that had another adjacent point which weren’t drawn the fi rst time. The pen goes down, and the process happens again, just with a new starting point. This same process happens over and over, With all this established, it was time to fi gure out the until the pen is back at that very fi rst point without any system for actually drawing pictures. Since each drawing adjacent points to draw. is basically just a map of X-Y coordinates, we needed to By now, there should be some lines and curves, all fi gure out exactly what one coordinate meant. We ended up connected to each other. To keep drawing, Bot Ross starts deciding that each coordinate — corresponding to one pixel over. It fi nds a new undrawn point, places the pen, and on an image — would be 1 mm by 1 mm. looks for adjacent pixels. With this algorithm running over Our motor control code could easily support drawing and over (and over) again, eventually every single pixel will millimeter-long lines, which gives picture drawing great be found and the entire image will be sketched. precision. With our motors controlled and a convention for This process is based on a common algorithm called how an image should appear, we now needed a way to get depth-fi rst search2, which is often used for robots to pictures involved. This required a script for image processing, traverse their surroundings. In this case, we used it to give or having a computer look at a picture and turn it into arrays instructions for a robot to draw a picture. of numbers. With software and hardware in place, it was time to The goal here was to break an image down to a map of perfect the mechanics behind picture drawing. X-Y coordinates, then fi gure out the best way for Bot Ross to connect the dots in that map. Since images would be The Build coming from a computer rather than the microcontroller, we decided to write this part of the code using Python to take We spent a lot of time writing code and designing advantage of easier-to-use arrays and the OpenCV library for circuitry to make the plotter run well, but to put it all computer vision and image processing. together in one system, we needed to physically construct Using OpenCV, we can use an algorithm called the Bot Ross. The system had three degrees of freedom; two of Canny algorithm to do an edge detection of an image. An which were the stepper motors moving along the X and Y “edge” is any kind of boundary that you can see between axes, with the third degree being the pen moving up and shapes in an image. This algorithm takes an image and down. Take a look at Figure 5. creates that X-Y map of edges. An important part of using the stepper motors was 42 SERVO Issue-1.2020 having a method of turning their rotational motion into linear motion. This was done using two lead screws which are similar to threaded rods, and allowing the turning motion of the stepper motors to become linear motion. Since the stepper motors only have a metal shaft to use for any kind of fi xture, collars were needed to connect the lead screw to the motor. Also, each lead screw has a nut which connects to the object that is moving across the axis. For the big stepper motor, the nut was attached to the smaller arm that held the second smaller motor. For the smaller stepper motor, the nut was attached to the block that held the actuation mechanism for the pen. While one end of the lead screws was fi xed to the shaft of the stepper motors with collars, the other ends were held in place at a level height by custom 3D-printed screw holders. These holders were essentially blocks, with openings to allow the screws to be propped up instead. To allow the smaller arm to move smoothly when the big motor was stepping, we used a drawer slide (Lowe’s item #380974) to reduce the frictional resistance on the arm when moving. These slides are mechanisms found in drawers pretty much anywhere. They’re basically rails with supporting wheels that allow the support to move across it with little friction. This reduction of friction was important due to the nature of our design. Any friction on the free end of the smaller motor arm would cause “missed” drawing as the Figure 6: The rack and pinion mechanism. arm would bend without the pen moving the specifi ed distance. We sprayed WD-40 on the drawer slide as well to was a highly important component to our project because ensure the support was not sticking to any part of the slide it allowed us to fi ne-tune the position of the pen when rail when moving the entire distance across. drawing. We wanted our artistic creation to be great! To make the pen move up and down, a 3D-printed A rack and pinion works similar to the way the lead rack and pinion mechanism obtained from the Thingiverse screws work in our project. The pinion is a gear that website was used in conjunction with a micro servo to allow attaches to a servo, and when it rotates, it moves the rack the pen to move linearly up and down. This mechanism holding the pen. Refer to Figure 6.
Parts List Resources Link to Project Web Page: http://people.ece.cornell.edu/land/ courses/ece4760/FinalProjects/f2019/bas335_rns85_sdd58/ ITEM QTY bas335_rns85_sdd58/bas335_rns85_sdd58/index.html Threaded Rods 2 Link to Project Video: https://www.youtube.com/ Stepper Motors 2 watch?v=UoiOHu-NbZk&t=3s Shaft Couplers 2 OpenCV Python Library: https://opencv.org Drawer Slide 1 Explanation of Depth-First Search: https://en.wikipedia.org/wiki/ Big Board 1 Depth-fi rst_search Port Expander 1 Rack and Pinion 3D object fi les: https://www.thingiverse.com/ MicroStick2 1 thing:3170748 PIC32MX 1 Richelieu 20” drawer slides (purchased at Lowe’s): https://www. Jumper Cables 19 lowes.com/pd/Richelieu-2-Pack-20-in-Drawer-Slide/50041730 Header Pins 8 Microchip Documentation on Stepper Motors: https://www. Dual H-Bridge Motor Drivers (four pack) 1 microchip.com/stellent/groups/SiteComm_sg/documents/ PLA for 3D Prints DeviceDoc/en543050.pdf SERVO Issue-1.2020 43 Figure 8: Original image of Elon Musk (left) and drawn image of Musk (right). The left image by Duncan.Hull is licensed under CC BY-SA 4.0. The image by Duncan.Hull is shown cropped in Figure 8 as that was the optimal aspect ratio determined to be used for the plotting system. The image was not modifi ed in any form other than cropping.
The fi nal part of the construction was attaching warped from its previous use, so we had to place another everything to the wooden base. This project was done platform on the base with small supports underneath to with a relatively small budget, so we resorted to the cheap create a level drawing surface. (yet very effective) method of hot gluing to attach all the components onto the base. As we later noticed, this wooden base was quite Happy Accidents As with all engineering projects, problems and bugs arise mid-build and need to be addressed. Nothing is ever perfect on the fi rst try, and Bot Ross was no different. For the fi rst few runs of Bot Ross, the robot would slowly start drawing the image over itself, getting lost on the large page. Thankfully, we included an onboard display which allowed Bot Ross to tell us that it thought it was in the right position. Figure 7 shows an image of the distortion that we kept on noticing. No matter what we tried, we couldn’t fi gure out why the image
Figure 7: Distorted image (left) and corrected image (right). 44 SERVO Issue-1.2020 would keep on shifting to the left. It wasn’t until the late algorithm was run on only the upper portion of the digital hours of the night that we fi nally fi gured out what was image, as shown by the drawing. plighting Bot Ross. Just like having a proper canvas to paint Although the contoured version of the image doesn’t on, we realized that Bot Ross didn’t have a level surface to look exactly like the original, almost all of the portrait outline draw on. and facial details are captured. The suit is the most clear When the pen was down and moving to the right part; you can even see the outline of his collar. (uphill), it would go slower than if it was drawing downhill. Since the stepper motors were not that fast, it took However, this proved to be no problem as it was constant about 15 minutes to draw the picture of Musk, but the time and calibrated out. was different for every image. The aspect ratio of the drawn By simply adding a correction factor — an additional image is slightly different from the original, but that could step for every 10 going uphill — we were able to counteract be easily fi xed by adjusting the number of steps between the force of going uphill and re-center the drawing. coordinates in the X and Y axes. As stated, in all projects bugs are going to appear, and We learned a lot from the challenges this project it was extremely useful for us to have accounted for the presented and succeeded in creating a “masterpiece.” potential for bugs from the get-go with the inclusion of the Designing Bot Ross was a rewarding experience in debugging terminal. collaborating with a team towards a common goal and learning how to effi ciently use resources to make a great The Masterpiece project. SV After weeks of long hours spent in the lab, we did it. We had fi nally drawn a complete image. We fi nally drew a To post comments on this article and fi nd picture of the tech mogul, Elon Musk (Figure 8). any associated fi les and/or downloads, go to Due to the constraints of the plotter, the edge detection www.servomagazine.com/magazine/issue/2020/01.
SERVO Issue-1.2020 45 By Theron Wierenga BBuildinguilding a LineLinearar AActuatorctuator
While doing some thinking about building a walking bird robot, I researched purchasing linear actuators. What I found is that linear actuators are fairly expensive — especially if you’re an amateur robot builder with a limited budget. This led me to thinking about what it would take to build my own linear actuators.
46 SERVO Issue-1.2020 linear actuator functions very simply. By powering This ball bearing is 9/32 inches wide with an outer the DC motor, the arm moves out linearly; by diameter of 3/4 inches and a 1/4 inch inner diameter. The reversing the polarity to the DC motor, the arm bottom of the inner arm tube has two circular holes at the Amoves in. Circular motion is turned into linear ends to press-fit 8x3 mm neodymium disk magnets. The motion. A linear actuator is a simple on and off bottom of the square body has slots in it to hold small Hall- device with no control over the position of the arm. To avoid effect 3144 sensors. Refer to Figure 1. extending the arm too far in or out, limit switches are often A single Hall-effect sensor on the bottom (at the used which must be continually read by a microcontroller. forward end of the outer body) can sense the magnets at A servo linear actuator is a more complicated device. each end of the inner tube. This then becomes the limit However, it does have the ability to position itself. This can switches but without the mechanical complications of micro be done through the use of servo motors or DC motors that switches. If additional specific positioning of the inner arm have feedback or encoders attached to them or by sensors is desired, additional Hall-effect sensors can be added in the to control positioning. My requirements included simple slots. positioning. The complications of this design would be difficult The arm needs to move out to position X and then for the amateur builder if it were to be constructed from return to position Y, with some speed control. This could be something like aluminum tubing. Fortunately, 3D printing is done with limit switches at the needed positions and pulse a natural for this design and solves a number of construction width modulation (PWM) to control the speed. challenges. Plus, it allows for accurate sizing and alignment. Some further thinking and a few sketches later, the Refer to Figure 2. idea of using Hall-effect sensors instead of limit switches Selecting an appropriate DC motor was a challenge, but was added to my plans. A square tube within a square tube I was fortunate in my first choice. Electronic Goldmine has a was envisioned, to be 3D printed, forming an actuator arm small surplus Johnson brand DC motor (#G9332), reportedly within a body. 1-1/16 inches in diameter, 1-1/2 inches long, 6-24 volts, At the back end of the inner arm is a captured 1/4 - 20 and with a 1/16 inch shaft. The shaft turned out to be .090 nut, and just outside the back end of the square body is a inches not .0625. captured ball bearing connected to a threaded 1/4 - 20 rod Because some spur gears are available for 1/8 inch that moves the inner arm by turning in the captured nut. shafts, I increased the shaft diameter by gluing 1/8 inch
Figure 1. Concept diagram, top view.
To post comments on this article and find any associated files and/or downloads, go to www.servomagazine.com/magazine/issue/2020/01.
SERVO Issue-1.2020 47 diameter thin wall brass tubing to the shafts with marine epoxy. This worked quite well and doesn’t appear to have added any vibration. I measured the no-load current of this motor to be about 160 milliamps and the stall current three amps. For gears, I ordered a number of 48 pitch Traxxas spur gears with 12, 21, 26, and 31 teeth and an 1/8 inch shaft size from Amazon. Some experimenting was done with the Hobbypark 17, 21, 26, and 29 teeth gear set from Amazon. The Traxxas gears run a lot smoother. There are other sets available with differing numbers of teeth. With different combinations of these gears, one can increase or decrease the speed and torque of the motor. For each pair of gears, the only change in the design is the height of the Figure 2. 3D model from Sketchup, without the top pillow block to hold the center line of the motor. Spur gears must be carefully captured ball bearing in place. aligned, and any misalignment will cause loss of power, wear, and noise. My goal was to have the linear actuator be able to have a speed of 50 mm/sec. Using the 17-tooth gear on the motor and the 26-tooth gear on the shaft, it averages 84 mm/sec with no load. Having the arm lifting a 550 gram load, it averaged 67 mm/sec. Refer to Figures 3 and 4. Another motor considered was a Tsiny TRS-550PC from www.tsinymotor.com and available on Amazon. This motor is considerably larger at 37-1/2 mm in diameter and 64-1/2 mm long. With a 12 volt power supply, the no-load current is 1.35 amps; nominal current is over 10 amps; and stall current is a whopping 76 amps. When I clipped leads onto this motor from a 12 volt lead acid battery, I wasn’t holding the motor very tightly in my hand. On start-up, it jumped out of my hand. This would be a good candidate for some heavy lifting. It will need a hefty motor driver as well; something like the BTS7960. While it’s advertised as a 43 amp driver, this is Figure 3. Inner arm, top view without top cover. not a continuous current rating. At 20 amps continuous, this driver will run very hot. Construction The majority of time spent on this project was designing the 3D models for the parts and then getting them to print at the exact sizes needed. 3D plastic shrinks on cooling and a 1/4 inch hole ends up being something like 0.243 inches. This will vary depending on the brand of plastic used and even the color in some cases. PLA was chosen for its ease of use. One can estimate the shrinkage for the various types of plastic, but nothing works better than printing, testing, measuring, and printing again. It’s very important to get all the parts to fit snugly and be well aligned. All the moving parts need to be able
Figure 4. Inner arm, bottom view with circular openings for magnets. 48 SERVO Issue-1.2020 to glide smoothly without binding or drag. My models went through many iterations for different designs and sizes. The stroke length on my model is 3-1/2 inches or 88.9 mm. This can be easily lengthened or Figure 5. Threaded rod assembly. shortened by changing the length of the inner and outer tubes and the threaded rod. Included in the downloads are all the Sketchup files and their object files for 3D printing. I used Cura 4.6.1 for my slicer. After 3D printing the inner arm, Figure 6. Model with separate motor mounts before installation of the pillow block over the a 1/4 - 20 stainless steel nut was ball bearing. inserted into the capture space and then the cover screwed down with 1/4 inch 4-40 flat head machine screws. The two magnets are then press-fit into the openings on the bottom. Be sure you have the correct side of the magnet facing out for the Hall-effect sensor. Figure 7. A direct drive model, with the pillow block in place over the bearing. A 6-1/4 inch piece of 1/4 -20 threaded rod was cut and the end This blob of epoxy was then turned down on a lathe to 0.25 turned down to 1/8 inch to accommodate the spur gear. inches to fit snugly in the bearing. This aligns the threaded Double-check the length of the threaded rod because if it’s rod better with the bearing. Several different models were too long, it can hit the end of the inner tube before the built; some with an attached motor mount and others with Hall-effect sensor reacts to the magnet. A small lathe is separate motor mounts. A separate motor mount allows for necessary to get good alignment. Care must be taken not to only changing the motor mount when different size gears crush the threads of the threaded rod with the lathe chuck are used. The gears were left exposed, but additional walls jaws. could be added to enclose them. It would also be fairly easy The threaded rod gets a 1/4 - 20 nut, a 3/4 inch to upscale this design with larger tubes, thicker walls, and a diameter ball bearing, a 1/4 inch lock washer, and a final more powerful motor. 1/4 - 20 nut. I used stainless steel for the nuts and lock A model with the motor directly attached to the washer. This assembly is then placed into the capture area threaded rod is shown in Figure 7. The shaft coupling used at the back end of the outer tube. It’s held in place with a is a 3 mm to 3 mm flexible coupling 25 mm in length and 3D printed pillow block that is held down with four 4-40 flat 18 mm diameter (found on Amazon). The 3 mm holes head machine screws 5/8 inches long. With the chosen gear were drilled out to accommodate the 1/8 inch shafts. This placed on the end of the 1/8 inch axle coming out of the diameter is only about 0.007 inches larger. threaded rod, the assembly should turn easily with very little This version performed better than expected. Using friction. Refer to Figures 5 and 6. the same G9332 motor, the no-load speed was 93 mm/sec There is an inherent problem here with alignment. While and with the 550 gram load 77 mm/sec. The use of geared the ball bearing inner diameter is close to 0.25 inches, the drives allows for more torque when gearing down, and threaded rod is not; it’s something like 0.232 inches. When therefore high lifting power. With a direct drive, one does the two 1/4 -20 nuts are tightened down, the threaded not have that option. With the use of PWM to a direct drive rod will not be aligned with the center line of the bearing or spur geared motor, the speed can only be reduced and opening, causing vibration. with a loss of torque. Refer to Figure 8. To improve this, I coated the portion of the threaded Direct Drive Spur, Geared Down Spur, Geared Up rod that goes inside the bearing with marine epoxy. Torque (Lifting Power) Fixed Higher Lower Speed Fixed Slower Faster Figure 8. Drive type variables at full power. Noise Lower Higher Higher SERVO Issue-1.2020 49 Two DC motors can be driven from one of these modules and it can handle 25 watts or about two amps using a Figure 9. L298N motor 12 volt battery for power. These modules can be digitally driver module. programmed to run a DC motor forwards or backwards, and can also use PWM to vary the speed of the motor. A simple circuit to drive a single DC motor with feedback from a Hall-effect sensor is shown in Figure 10. Pin D9 on the Arduino Nano is connected to ENA on the driver board, D8 to IN1, and D7 to IN2. The Hall-effect sensor output is connected to A5, which is used as a digital input pin. Note that the jumpers must be removed on the Enable pins ENA and ENB of the L298N module to use PWM. These jumpers are shown in place on the Fritzing diagram in Figure 10. Although an Arduino Nano was chosen for the microcontroller, just about any other microcontroller could be used. A printed circuit board (PCB) was designed to fit an ExpressPCB standard MiniBoard at 3.8 x 2.5 inches. This circuit uses a single Nano to drive two of the L298N driver boards (mounted vertically) and headers for eight 3144 Hall- Spur gears are known for their noise and a direct effect sensors. The layout for this board can be found in the drive improves this. Helical gears would be another option, downloads. All the pins on the Nano are used, except for D0 although I had difficulty finding small ones in the sizes I and D1 which are used for the serial monitor. wanted. The schematic for the linear actuator drive board is shown in Figure 11. Motor Driver and Hardware Software An L298N motor driver (Figure 9) was used to power the motor. These are widely available and inexpensive. A program for multiple linear actuators to run on the
Figure 10. A circuit to operate a single motor with the L298N driver and Hall-effect sensors for feedback.
50 SERVO Issue-1.2020 Figure 11. Design of linear actuator drive board.
Nano was created and designed for use with the circuit built on the PCB. The program has a few simple functions to control four linear actuators. The functions available are:
// Retract the actuator arm until it hits the home position void homeMotor(int motor, int hall, int pwm)
// Soft start by increasing PWM before full power bool softStartPWM(int motor, int setting, int maxPWM)
// Turn motor on, off, brake or free, turning at full power bool setMotor(int motor, int setting)
// Turn motor on, off, brake or free turning using PWM bool setMotorPWM(int motor, int setting, int pwm) false; setMotorPWM(motor, MOTOR_IN, pwm); // Read the output of a Hall Effect sensor, a low read means contact while (readHall(hall) == HALL_OFF) {}; int readHall(int num) setMotor(motor, MOTOR_BRAKED); return true; // Run the motor for ¼ second so travel can be } measured void speedCheck() The setMotor() function is quite basic and is only The homeMotor() function is shown below and is lengthy because it can service four motors. After doing an straightforward. It first checks if a correct motor has been error check for correct input, it uses a switch statement to defined and if not, it returns with a false. Next, it turns select which motor, then another switch statement to select the motor on pulling the inner tube inwards, then begins the setting: reading the Hall-effect sensor until it turns on. It then brakes the motor and returns a true: // This function is used to turn a motor ON, OFF, BRAKED or OFF (free turning) at full power bool setMotor(int motor, int setting) // Return motor to home positon, which is fully { retracted if ((motor != MOTOR_A) && (motor != MOTOR_B) bool homeMotor(int motor, int hall, int pwm) && (motor != MOTOR_C) && (motor != MOTOR_D)) { return false; if ((motor != MOTOR_A) && (motor != MOTOR_B) && if ((setting != MOTOR_OFF) && (setting (motor != MOTOR_C) && (motor != MOTOR_D)) return != MOTOR_BRAKED) && (setting != MOTOR_IN) && SERVO Issue-1.2020 51 Parts List ITEM SOURCE 1/4-20 Threaded Rod Home Depot or Lowes 1/4-20 Nuts and Lock Washers, Stainless Steel Home Depot or Lowes 4-40 Flat Head Machine Screws and Nuts, 1/4, 3/8, and 5/8 lengths Home Depot or Lowes 4-40 Pan Head Machine Screws 1/2 inch, All Screws and Nuts Stainless Steel 48 Pitch Spur Gears Traxxas 2412, 2421, 2426, 2428, and 2431 Amazon or Local Hobby Shop Hobbypark 48 Pitch Gear Set, 17, 21, 26, and 29 Teeth Amazon Xnrtop 3 mm to 3 mm Shaft Coupling 25 mm length, 18 m diameter Amazon 8 x 3 mm Neodymium Disk Magnets Home Depot, Lowes, or Amazon Loctite Marine Epoxy Amazon or Menards White Lithium Grease Home Depot or Lowes Johnson DC Motor, #G9332 Electronic Goldmine L298N Motor Driver Board eBay or Amazon Battery or Power Supply, 12 volt/3 amp Home Depot or Lowes Arduino Nano eBay or Amazon Hall-effect 3144 Sensors eBay Printed Circuit Board or Breadboard ExpressPCB Header Pins and Header Jumpers eBay or Amazon Hookup Wire, Solder Home Depot or Lowes Ball Bearing, 3/4 inch OD, 1/4 inch ID, 9/32 wide Amazon
If Printed Circuit Board is Built: LM7805 Voltage Regulator eBay or Amazon 1,000 µF 6.3 volt Electrolytic Capacitor, .1 µF Capacitor eBay or Amazon
Tools Needed: Small Lathe 3D Printer, Plastic Filament, Cuda Software, and Optional 3D Design Software.
(setting != MOTOR_OUT)) return false; break; switch (motor) case MOTOR_OUT: { digitalWrite(IN_A1, HIGH); case MOTOR_A:switch (setting) { digitalWrite(IN_A2, LOW); case MOTOR_OFF: digitalWrite(ENABLE_A, LOW); digitalWrite(ENABLE_A, HIGH); break; break; case MOTOR_BRAKED: } digitalWrite(IN_A1, LOW); break; case MOTOR_B:switch (setting) digitalWrite(IN_A2, LOW); { case MOTOR_OFF: digitalWrite(ENABLE_A, HIGH); digitalWrite(ENABLE_B, LOW); break; break; case MOTOR_IN: case MOTOR_BRAKED: digitalWrite(IN_A1, LOW); digitalWrite(IN_B1, LOW); digitalWrite(IN_A2, HIGH); digitalWrite(IN_B2, LOW); digitalWrite(ENABLE_A, HIGH); digitalWrite(ENABLE_B, HIGH); 52 SERVO Issue-1.2020 break; break; case MOTOR_IN: } digitalWrite(IN_B1, LOW); return true; } digitalWrite(IN_B2, HIGH); This program doesn’t need to be run with the included digitalWrite(ENABLE_B, HIGH); PCB design. Point-to-point wiring can be used between break; the Nano, Hall-effect sensor, driver board, and motor. By case MOTOR_OUT: digitalWrite(IN_B1, HIGH); following the pin assignments in the program shown below, it can be used as a general interface for one to four linear digitalWrite(IN_B2, LOW); actuators. digitalWrite(ENABLE_B, HIGH); Pin assignments can also be changed in the program to break; suit user needs. } break; case MOTOR_C:switch (setting) #define HALL1 A5 { #define HALL2 A4 case MOTOR_OFF: #define HALL3 2 digitalWrite(ENABLE_C, LOW); #define HALL4 4 break; #define HALL5 12 case MOTOR_BRAKED: #define HALL6 13 digitalWrite(IN_C1, LOW); #define HALL7 A7 #define HALL8 A6 digitalWrite(IN_C2, LOW); #define ENABLE_A 9 digitalWrite(ENABLE_C, HIGH); #define IN_A1 8 break; #define IN_A2 7 case MOTOR_IN: digitalWrite(IN_C1, LOW); #define ENABLE_B 3 #define IN_B1 6 digitalWrite(IN_C2, HIGH); #define IN_B2 5 digitalWrite(ENABLE_C, HIGH); #define ENABLE_C 11 break; #define IN_C1 A0 case MOTOR_OUT: #define IN_C2 A1 digitalWrite(IN_C1, HIGH); #define ENABLE_D 10 digitalWrite(IN_C2, LOW); #define IN_D1 A2 #define IN_D2 A3 digitalWrite(ENABLE_C, HIGH); break; A copy of this program is included in the downloads. } break; case MOTOR_D:switch (setting) Conclusion { case MOTOR_OFF: digitalWrite(ENABLE_D, LOW); break; This was an enjoyable project, even though many hours case MOTOR_BRAKED: were spent getting things “just right.” For the builder, it’s digitalWrite(IN_D1, LOW); imperative that everything runs smoothly with little friction. digitalWrite(IN_D2, LOW); It’s worth the extra effort to reprint something (like the inner tube) if it sticks slightly when moving in and out. With the digitalWrite(ENABLE_D, HIGH); small motor used, it doesn’t take much friction to bind and break; case MOTOR_IN: stall the motor. digitalWrite(IN_D1, LOW); When the threaded rod and its bearing are inserted into the main body, be sure everything can turn easily using a digitalWrite(IN_D2, HIGH); thumb on the gears or coupling. A small amount of white digitalWrite(ENABLE_D, HIGH); lithium grease can be used on the gears and threaded rod break; to reduce friction. The pillow block that holds the bearing in case MOTOR_OUT: digitalWrite(IN_D1, HIGH); place should fit snugly, but do not overtighten it. Using 3D printing allows for custom attachment digitalWrite(IN_D2, LOW); methods, depending on the use intended for the linear digitalWrite(ENABLE_D, HIGH); actuator. My models simply have a mounting hole at each break; end, but a simple redesign would allow a better integration } into the model the linear actuator moves. SV SERVO Issue-1.2020 53 Versatile Stepper
Control By William Cooke
54 SERVO Issue-1.2020 Stepper motors are a staple of robotics. They’re great for precise speed and positioning. It’s also easy to control one. But what about two, or three? With different step rates? For different amounts of time? While your microcontroller continues doing other tasks? It can quickly become difficult, but with the technique presented here you can do all that and use only about two or three percent of the microcontroller’s time.
going to borrow a method often used for generating radio and audio signals and use it to generate step rates for motors. We’ll I’mbe able to step several motors, with each motor having individual control of the step rate and number of steps. The code uses interrupts and runs mostly in the background, allowing your controller to continue doing whatever else it needs while the steppers continue stepping along. The example uses an Arduino, but you can apply it to almost any controller. Brief Review of Steppers
Let’s take a brief review of how to control a stepper. We’ll only cover the parts relevant to us, so if you want to know more about steppers, check out the References. For control purposes, there are two basic types of steppers: bipolar and unipolar. Refer to Figure 1. A unipolar motor appears to the control circuits as (usually) four motor windings. Those four windings are connected together at one end, either internally or externally to the motor. That mutual connection is attached to one side of the power supply, most often the positive side. By connecting the other end of the winding to the other side of the supply, our circuit can energize that winding. We only control one side of the supply. Hence, the name “unipolar.” A bipolar motor, however, usually has two windings. We control both
Figure 1. Schematic diagram of unipolar and bipolar stepper motors with representative driver circuits. The circuits are incomplete and only used for reference. SERVO Issue-1.2020 55 Figure 2. Full-wave, half-wave, and half- step stepping patterns for unipolar and bipolar motors. The table entries for the windings match those in Figure 1.
other two. The driver electronics may be as simple as four transistors for a unipolar motor. H-Bridge chips are typically used for bipolar motors, but a DPDT relay is also effective. In the example system shown, I used a ULN2803A (with eight Darlington pair transistors) for two unipolar motors and a SN754410 dual H-bridge to control one bipolar motor. To control the motor, we send the bit pattern to the winding drive ends of both windings. Our control circuit (using an H-bridge electronics. Stepping through the table of bit patterns — or something similar) can connect either end to either side either forward or backward — steps the motor forward or of the power supply. backward, respectively. When we reach one end of the If we connect one end to positive and the other to table, we wrap around to the other and continue on. ground, current will flow in one direction. If we reverse both ends, current flows in the other direction. If both ends are Controlling One Motor connected to the same side of the supply, no current flows. So, now we can energize the winding in either direction or Once we decide to use a stepper, we may want to step not at all. That’s why these are called “bipolar.” some number of steps per second for a certain number of It would seem the control of these two types of motors steps. After a bit of thinking, we dive in and write some would be very different. However, it turns out our software Arduino code. Maybe it looks like this: can control them exactly the same. Both types have four connections. The unipolar has connections to one end of uint8_t fullWaveTable[] = { 0x03, 0x06, 0xc0, 0x09 }; // Full Wave table four windings. The bipolar has connections to two ends of 0011, 0110, 1100, 1001 two windings. In both cases, if we energize the windings in the correct sequence, the motor will step. void stepMotor(uint16_t steps, uint8_t delayTime) { A single output bit can either energize or not energize for(uint16_t step = 0; step < steps; step++) a winding in a unipolar motor. In a bipolar motor, two bits { together determine if a winding is energized and in which uint8_t outputValue = fullWaveTable[step % 4]; sendToMotor(outputValue); // Send this bit direction. A sequence of patterns applied to either motor pattern to controller makes it go around. Reversing the sequence makes it spin delay(delayTime); the other direction. It turns out that both motors use the } } same patterns and sequences. There are three common sequences of patterns: full- That will work. It will step a motor up to 65,535 steps wave, half-wave, and half-step. The full-wave and half-wave with a delay between steps of 0 to 255 milliseconds. take a complete step with each pattern change. The half- Unfortunately, it has problems. step takes half a step (as expected) for a total of twice as Perhaps the most obvious problem is that the Arduino many steps. Look at Figure 2 for all three patterns and how can’t do anything else while the motor is running. If we they apply to both types of motors. ask it to step the motor 10,000 steps with a delay of 20 The full-wave sequence energizes two windings at once milliseconds (50 steps per second), our Arduino will be and gives the most torque. It also uses the most energy. tied up doing nothing else for 10,000 * 20 = 200,000 The half-wave sequence only energizes one winding at a milliseconds. Over three minutes. time. Although it also takes full steps, the steps are halfway A bit less obvious is what if we want a step rate of 750 between those of the full-wave sequence. Since only one steps per second? A delay value of 1 gives about 1,000 steps winding is energized, it has less torque but uses less power. per second and a value of 2 gives 500 steps per second. The half-step sequence is a combination of the two We could use something like delayMicroseconds() and that previous sequences. It takes twice as many patterns but might fix the timing problem, but it doesn’t help with the gives twice as many steps. It also gives torque between the other issues. Plus, it adds plenty of problems of its own. We 56 SERVO Issue-1.2020 won’t pursue that any further. Fractional Steps Here’s another problem. Suddenly, we remember the robotic arm we’re building needs three motors moving What if we could take an arbitrary fraction of a step? simultaneously but at different rates, and may not start and Say, 4/5 (0.8) or 3/4 (0.75)? With 1,000 interrupts per stop at the same time. second and taking 4/5 steps per interrupt, we could have I encourage you to try to extend the function above 800 steps per second. Or, 3/4 would give us 750 steps per to handle two motors with different numbers of steps and second. It turns out we can. different stepping rates. If you manage to make two work, Radio and audio frequency signal generators, arbitrary try three. waveform generators, “wavetable” sound systems, and various other types of signal generating systems use a A Better Way technique called Direct Digital Synthesis (DDS). We can borrow DDS to generate our stepper waveforms. We can take a big step forward by using interrupts. DDS is a fascinating technique and I encourage you to An interrupt is like a phone ringing. You can be working check the References to learn more about it. Let’s apply it on something and paying no attention to your phone, but to making things spin! when it rings, you stop what you’re doing and handle the Instead of an audio or radio signal, our waveform is the call. When complete, you start back right where you left off. pattern sequence we chose to drive our stepper. By taking An interrupt in a microprocessor is like a telephone ring. fractional steps at each interrupt, we can get almost any The processor pays no attention to some desired step rate up to the maximum, device until an interrupt is activated; it which is the interrupt rate. stops what it’s doing and saves enough The trick is a variable called a “phase information to come back later. It does accumulator.” The variable is broken into whatever is needed by the interrupt and two parts: two or three bits are used to goes back to what it was working on. index into our pattern sequence table; If we have some device interrupt the rest represent a fraction. the processor at regular intervals, we As an example, let’s create a five-bit can handle the stepper motor(s) without phase accumulator and use the full-wave using any delays. Instead of spinning our table. For either the full-wave or half- wheels waiting on time to pass, we do wave tables, we use the most significant other tasks that need to be done. two bits, and for the half step table, the For example, if we have a hardware upper three bits. Refer to Figure 3. timer interrupt the processor 1,000 When our interrupt calls, we add a times per second, we can step our motor number to the phase accumulator. Then, each time. If we want it to step slower, we take the most significant two bits we can step every second or third or to index into the step table. We output whatever time. That solves the problem the value at that location to the motor of the controller spending all its time controller. waiting. It also makes it fairly simple to Those extra three bits represent control more than one motor. We still a fraction. Three bits represent eight have the issue of resolution; we can have different numbers from zero to seven, or 1,000 steps per second or 500 steps per 1/8 of a step. Adding one to the phase second, but not 750 or 800. accumulator each time effectively takes Interrupts are a huge topic by 1/8 of a step. If we add four each time, themselves. It’s important to keep the we take a half step (4/8). Adding eight Interrupt Service Routine (ISR) short and each time will take a full step, which is fast. It’s also important to protect any the max. data that may be accessed by both the In Figure 3, the entries highlighted interrupt and the main code. in yellow represent the steps taken with Often, that means turning off a five-bit phase accumulator, a four-entry interrupts in the main code before Figure 3. An example five-bit phase table, and an increment of five. accessing that data and turning them accumulator showing how steps are You can see some numbers are back on after. You can see examples taken with an increment of five. The output more than once, but that has no in the project we’ll be discussing, plus individual patterns are color-coded on effect on the result. The motor won’t Reference 2 has some good basic the right and the phase accumulator care if you re-write the same value to it. information. values are highlighted in yellow. Increments can be any value from SERVO Issue-1.2020 57 size is 16 bits. With a four- entry table, 14 bits are left for the fraction, giving a step resolution of 1/(2^14), or 1/16384 (0.000061) step. Again, at 1,000 steps per second, we get 1,000 * n/16384 steps per second.
Here is the general formula:
StepsPerSecond = InterruptRate * Increment / (2^FractionBits)
We rearrange that to be more Figure 4. Schematic diagram of the useful and find the example system showing the Arduino needed increment: Nano, the ULN2803 used to drive two unipolar motors, and an SN754410 StepRate = used to drive a single bipolar motor. InterruptRate * n/16384 rearranging: zero (motor stopped) to eight (one step per interrupt.) Our n = StepRate * 16384 / InterruptRate step rate can be 1,000 * n/8: 0, 125, 250, 375, 500, 625, 750, 875, and 1,000. If we increase the size of the phase To find n for 750 steps per second: accumulator, that leaves more bits for the fraction. A good n = 750 * 16384 / 1000 = 12,288
or for 800:
n = 800 * 16384 / 1000 = 13,107.2.
Round down to 13,107 for 799.99 steps per second — probably close enough. If you really need better resolution, you can go to a 32-bit phase accumulator, but that isn’t often necessary.
What if we want to go really slow?
Photo 1. The example prototype board with one unipolar and one bipolar motor attached. 58 SERVO Issue-1.2020 n = 0.1 * 16,384 / 1,000 finish. It’s simple to do. We write the value to the compare n = 1.64 round to 2 register, then enable the interrupt. We do that in the setup() StepRate = 1,000 * 2 / 16384 = .122 steps per second function. Here’s the required code:
Remember that you can never take a step larger than // Set up the Compare A Register timer interrupt OCR0A = 0x20; // Set the compare A register to 1.00 or the motor will miss steps. That means for a 16-bit 0x20, away from 0 phase accumulator and two-bit index, the maximum value is TIMSK0 |= 2; // enable the compare A interrupt 16,384. For a three-bit index, it’s 8,192. In either case, we get one step every interrupt. Processing the Interrupt Note how simple it is to take a step and calculate the next one: When the interrupt occurs, the ISR is called. It looks much like any normal function, but there are some 1. Use the upper bits of phase accumulator to index differences. First, a special syntax is used to create it. table. Second, it must not have any inputs or return a value. 2. Output table value to motor driver. Interrupt routines should be short and fast. They should 3. Add increment to phase accumulator, rolling over only do the minimum amount of processing required. at either end. Anything that can be done outside the ISR should be. Interrupt programming can be full of headaches, but if That’s it! Simple and fast. Note that the increment can you’re careful, it isn’t too bad. I strongly encourage you to be negative, which steps backward. read up on the subject. The ISR is the heart of this method. The demo is for an Example Implementation Arduino, but most of the code is generic and should work unchanged or with small changes on most processors. The I promised an Arduino example. Let’s use an Arduino code in the listing is heavily commented, so I won’t discuss Nano, two unipolar motors, and one bipolar motor. We will most of it, but let’s take a look at the ISR. use the half-wave step table. It should be relatively simple to First, there are several variables that technically change how many and the types of motors or the step table aren’t part of the ISR but are critical to its operation. The used if you stay with an Arduino. first — stepper_phase — is an array that holds the phase Moving to a different controller will be more work; accumulator for each motor. you’ll need to know what timer, interrupt, and input/output The second is another array — stepper_stepSize — resources are available. The schematic is shown in Figure that holds the phase increment for each motor. Next is 4. The complete source code (Listing 1) is available in the stepper_steps, holding the number of steps for each motor downloads. to take. The last is a single variable called stepper_running to indicate if any motors are currently running. Getting the Interrupts Here’s the first half of the ISR. The part not shown is the output to the motors. You can see it in the main listing, but First, we need a source of interrupts. Most stepper you’ll likely need to change it to match your hardware. control applications will be well-served with an interrupt rate of around 1,000 interrupts per second. That will allow ISR(TIMER0_COMPA_vect) { almost any rate up to the interrupt rate. For a stepper with static uint16_t oldIndex[NUM_MOTORS]; // store 200 steps per revolution, we get five revolutions per second old index to test if we step or 300 RPM. if(stepper_running) The Arduino has a timer that interrupts close to 1,000 { times per second for the millis() counter. Timer 0 on the AVR uint16_t index; chip (the chipset used by most Arduinos) counts from 0 to uint8_t out[NUM_MOTORS]; 255 and interrupts when it rolls over to zero. Actually, 997 for(int mtr = 0; mtr < NUM_MOTORS; mtr++) times per second; close enough. The only problem is we { can’t hijack that interrupt. But we can hitch a ride! if(stepper_steps[mtr] != 0) { Timer 0 also has two compare registers not normally stepper_phase[mtr] += (uint16_t)stepper_ used that can interrupt when their value matches the stepSize[mtr]; counter. Let’s use one. index = stepper_phase[mtr] >> stepper_ indexShift; To avoid the interference to the millis() interrupt, we out[mtr] = stepper_stepTable[index]; set the compare register to a value other than zero. A good if(index != oldIndex[mtr]) choice is 0x20 (32 decimal); about 1/8 millisecond after the { rollover interrupt. Plenty of time for the millis() counter to stepper_steps[mtr]--; SERVO Issue-1.2020 59 oldIndex[mtr] = index; } The new output values found for the motors are } compared to the previous values held in the oldIndex array. } If they’re different, it means that motor took a step, so the // Code to output to motors goes here step count is updated. The only thing left to do is write the new table values out to the motor controllers. } } The ISR is short and simple. All the supporting code and interface functions are in Listing 1. In the example, I used direct port I/O. I highly The first line of the ISR is how we declare an ISR for recommend doing that. Using the digitalWrite function is the Arduino compiler. It looks like a function named “ISR” slow and can cause performance issues with your code as with the name of the interrupt in parentheses. For any well as the motors. Reference 6 has information on using Arduino based on the AVR chips, you can get the interrupt direct port I/O. name from Reference 4. If you’re using some other type of In all, the example controls three motors and uses only controller, you’ll need to find out how to use an appropriate about 2% of the processor’s time, leaving plenty for your interrupt. other code. You’ll have to research that on your own. Interrupt control is not a standard part of the C or C++ languages, so Conclusion every compiler does it differently. Even the same compiler may be different on different processors. You can take the example project here and use it Inside the ISR, we first declare an array named oldIndex immediately to control three motors. Of course, much more to hold all the previous index values, so we can determine if can be done by using it as a basis for your own ideas. a motor stepped in this iteration. By declaring the array as I hope you’ll take the techniques presented and go “static,” it holds its values between calls to the ISR. Another further. Interrupts are a powerful tool and most processors array named out temporarily holds the table values to write have many interrupt sources. to the motors. The phase accumulator/DDS method presented here is The main body of the ISR is a for loop that cycles useful for creating many different types of repetitive actions through all the motors. First, it checks if the motors are that don’t match timer interrupt rates. I look forward to running and skips everything else if not. If the motors are hearing what you create and perhaps reading about it in running, it adds the phase increment for each motor to the these pages. corresponding phase accumulator. The resulting phase is used to find the index and look As a final note, I’d like to thank my friend, Thomas up the needed pattern from the pattern table, stepper_ for asking the question that led to this article, and then stepTable. It saves that pattern to use later. encouraging me and reviewing it. SV
References / Further Reading 1. Douglas W. Jones on Stepping Motors 4. Interrupt Names http://homepage.divms.uiowa. AVR LIBC Interrupts edu/~jones/step/ https://www.nongnu.org/avr-libc/user- To post comments on this More than you ever wanted to know manual/group__avr__interrupts.html article and find any associated about steppers. Lists the interrupt names recognized by files and/or downloads, go to the GCC compiler for all supported AVR www.servomagazine.com/ 2. Arduino attachInterrpt() Reference processors. magazine/issue/2020/01. https://www.arduino.cc/reference/en/ language/functions/external-interrupts/ 5. Wikipedia entry on Direct Digital attachinterrupt Synthesis https://en.wikipedia.org/wiki/Direct_ 3. DS Tutorial digital_synthesis https://www.analog.com/en/analog- More good information on DDS. dialogue/articles/all-about-direct- digital-synthesis.html#Ask 6. Direct Port I/O on Arduino The Application Engineer—33: All About https://www.arduino.cc/en/Reference/ Direct Digital Synthesis by Eva Murphy PortManipulation and Colm, Slattery. A great introduction Explains how to use direct port I/O to Direct Digital Synthesis. instead of the Arduino single pin method.
60 SERVO Issue-1.2020 LLASERASER ALIGNMENT SYSYSTEMSTEM FORFOR YYOUROUR CNC ROUTER
By Roger D. Secura
I really like simple solutions to problems. For example, I designed and built a desktop CNC router some time ago. Although it works as expected, I was wasting a lot of time trying to align the center of my tool bit with the corner edge of my workpiece (wood). Then, like a fl ash of light (no pun intended), it hit me — use a laser to fi nd the edges of the wood. As it turns out, designing and building a laser system for my CNC router was really simple — just what I like. SERVO Issue-1.2020 61 WHAT TO EXPECT FIGURE 1 In this article, I’ll show you how to build a laser power supply circuit and how to construct a special bracket for your CNC router motor. Figure 1 shows the kind of output you can expect from my laser system. You’re going to like the fact that the power supply circuit only requires three components: the LM317T voltage regulator and two resistors. If that sounds good to you, keep reading. START WITH THE BRACKET
Figure 2 is the CAD drawing for the bracket that holds the two lasers in place. Figure 3 is a photo of the bracket after it was printed on my Alfawise U30 3D printer. Finally, Figure 4 shows the bracket mounted onto the CNC router motor. Aligning and mounting the bracket is really simple. Draw (pencil) a temporary 90° angle on your router table so that each leg of the 90° angle is an equal distance from the edge of your table. Place a board in the corner of the angle. Now, slide the bracket onto the motor and lightly tighten the #6- 32 machine screw. Rotate the two “line” lasers so they align themselves with the lower left-hand corner of the board (Machine Zero). In the Offset screen in Mach 3, enter: X = 4; as shown in Figure 1. Once aligned, level and tighten the Y = 4. Now, hit the ‘Go to Zero’ button on the main screen bracket around the motor. in Mach 3. Once you reach the designation X = 4 / Y = 4, Now, using the two laser lines as a guide, it’s possible the lasers will show you where to put the corner of your to center a router bit to any X and Y location on your table. workpiece. For example, move your cutting tool to the Home position Please note that this bracket was designed for my DeWalt DNP611 router. You may need to adjust the inner diameter (2.75”; see Figure 2) of the wooden bracket to fit your router or spindle motor. Be aware that in some cases, this bracket may interfere with the movement and/ FIGURE 2 or travel limits of your Z axis. Also, since both lasers have a focus adjustment screw on the front lens, you should unscrew the lens and add some Teflon tape (plumber’s tape) around the screw threads. Apparently, the screw is too loose (bad design/manufacturing) to maintain a set focus point. Watch out for the spring inside the laser. It will pop out. Finally, once you insert the 9/64” diameter mounting screws into the bracket, don’t over-tighten 62 SERVO Issue-1.2020 FIGURE 4
FIGURE 3 the screws. You could crack the bracket or the laser. OKAY, LET’S POWER UP THE LASERS
As you can see in Figure 5, the circuitry required to power the lasers is quite simple. I wanted to use 9V batteries, so I wouldn’t have to keep replacing them so often You’ll need to build two of these circuits; one for each (like I would with AA batteries). laser. Get some general-purpose PC board (2-7/8” L x 1-7/8” This requirement forced me to find a voltage regulator W) and hard-wire the components as shown in Figure 6. that could step down the voltage from nine volts to 3.3 volts You can glue or Velcro™ the battery clips to the — the laser’s operating voltage. Fortunately, the LM317T perfboard. This makes it easy to replace the 9V batteries met my requirement and did so with just a couple of extra when they get low. Figure 7 shows the circuit board components — two resistors! mounted onto the CNC machine. HOW THE CIRCUIT WORKS FIGURE 5 The LM317T voltage regulator is kind of amazing for what it can do. If you insert a potentiometer into the circuit (R2), you can vary the regulator’s output voltage (Vout) from 1.25V to 37V. The uniqueness of the LM317T is that you only need to add two resistors to get any output voltage between 1.25V and 37V. According to the datasheet, the LM317T must have a minimum of 10 mA flowing through resistor R1 or it falls out of regulation. In addition, by design, the regulator will always have a constant “reference” voltage level of 1.25V across R1, measured from pin 2 to pin 1. In order to determine the resistor value for SERVO Issue-1.2020 63 R1, we use Ohm’s Law as follows:
R1 = E/I R1 = 1.25V/10 mA R1 = 125 ohms FIGURE 6
As you can see, the value for R1 is 125 ohms. Let’s verify the minimum required current running through R1 is 10 mA:
IR1 = E/R IR1 = 1.25V/125 ohms IR1 = 10 mA
Since the current running through R1 is 10 mA, the series circuit of R1 and R2 dictates that the same 10 mA must run through R2. To calculate the resistance value for R2, we use the following formula (use 3.3V as our desired output voltage for the laser):
of 2.5V to 3V higher than the output voltage (Vout). In other words, if you need 3.3V for Vout (load), Vin must be at least 6.3V. Failure to adhere to this rule will cause the LM317T to fall out of regulation. The ‘minimum’ differential voltage between Vin and
R2 = 205 ohms
Now, insert R1 (125 ohms) and R2 (205 ohms) into the circuit. Take a voltmeter and check the output voltage and verify that it’s 3.3V, measured from the Vout terminal to ground. Notice that if we add the 1.25V across R1 and the 2.05V across R2, we get 3.3V at the Vout terminal. In other words, since the voltage across R1 (1.25V) never changes, FIGURE 7 we can control the output voltage at the Vout terminal (1.25V to 37V) just by varying the resistance of R2. If you’d rather not do the math, you can just make R1 equal to 125 ohms and use a potentiometer for R2. Now, turn the pot (R2) until the desired output voltage (measured from Vout to ground) is acquired. Remove the pot from your breadboard and check the ohm’s setting with an ohmmeter. Insert an equivalent resistor value back into the circuit. Again, check the voltage level at the Vout terminal to verify that you have the required output voltage; 3.3 volts for example. Done! Okay, now for a few caveats about the LM317T. First, the input supply voltage at pin 3 (Vin) MUST be a minimum 64 SERVO Issue-1.2020 Vout is called the “drop-out” remember, a laser beam reflected voltage (see the datasheet). If you FIGURE 8 off a shiny surface could accidently go below the minimum (3V), the target your eyes. regulator stops working. Please, don’t power-up your Secondly, the larger the 5 mW lasers until you have read voltage differential is between Vin ‘Sam’s Laser FAQ’ at www. and Vout, the more heat will be repairfaq.org/sam/lasersaf.htm. dissipated within the LM317T. It The 5 mW lasers used in this makes sense. article have a wavelength of 650 If, for example, you have nm-660 nm. Therefore, before you a 12V supply coming into the buy a pair of safety goggles, drop regulator at pin 3 (Vin) and your by YouTube’s website and enter Vout (load voltage) only requires the following text into the Search 3.3V, the LM317T will have to Box: “Choosing Laser Goggles” dissipate the voltage differential and “Testing Laser Goggles.” Don’t (5.7V) as heat. buy those cheap goggles and As a rule of thumb, the larger damage your eyesight! the differential, the more heat is Spend the extra money and generated. This means a heatsink get a good pair of safety glasses. may be required. You’re worth it! SV LASERS The two lasers used in this project (and shown in Figure 8) are called “line” lasers. In other words, you can buy lasers that project a single line, a cross pattern, or a dotted line pattern. Just be careful when buying your lasers online. Look for focusable 5 mW line lasers.
To post comments on this article and find WARNING! WEAR EYE any associated files and/or downloads, go to PROTECTION! www.servomagazine.com/magazine/issue/2020/01.
No project is worth damaging your eyesight. Any time you work with lasers, you need eye protection. Just PARTS LIST ITEM QTY DESCRIPTION PART# SOURCE R1 1 125 ohm, 1/4W, 1%, Metal Film 71-RM60D1250F Mouser R2 1 205 ohm, 1/4W, 1%, Metal Film 71-CMF50205R00FHEB Mouser IC 1 Voltage Regulator, 1.25V-37V 511-LM317T Mouser Laser 2 650 nm, 5 mW, Red, Focusable, “Line” Laser with Driver, 650ML-5-1235-2pcs-LM Amazon Working Voltage 3-5V, Dimensions 12 x 35 mm Goggles 2 Red, 635-660 nm Laser Protection NYBG Amazon Perf Brd 1 General-Purpose Grid-Style PC Board 276-150 RadioShack Screw 3 Machine, #6-32 x 1-3/4”, Phillips n/a Home Depot Nut 3 #6-32 Machine Screw Nut n/a Home Depot Washer 3 #6 Lock Washer n/a Home Depot Battery 2 9 VDC n/a (optional) Bat Snaps 2 9 VDC Battery Snaps & Contacts 121-0526/I-GR Mouser Bat Clip 2 9V Horizontal Battery Clip 12BH071-GR Mouser
SERVO Issue-1.2020 65 Alpha-Writer: Back from my school days, I remember my teachers giving homework that involved a lot of writing. I always wondered why there couldn’t be a robot that would do this task of writing homework for me. I’m glad it’s now possible to make this happen.
s I moved forward to do my Masters in Advanced to complete the build. The robot arm writes a designated Manufacturing, I had a course on industrial robotics. letter on a piece of paper when a particular button is While doing that class, our professor came up with pressed on the screen that’s part of the build. You can see Aan idea that a simple two-link robot could be used to what it’s writing in the camera using the Graphical User write letters. Figure 1 shows the simple two-link robotic arm. Interface (GUI). It’s called a 2R robotic arm since it has two revolute You can see the robot arm in action at https://youtu. joints connecting two links. At the end of the robot, there’s be/-GWMAvIMX4w. an end effector which, in our case, is a pen to write the letters. In this DIY project, I’ll show you how to make a simple Make Sure You Have These to computer-controlled letter writing robot from scratch. Once Begin you have all the required materials, it will take about an hour First, we’ll be making the two-link robotic arm. For this, we’ll need two servomotors with at least 10- FIGURE 1: Representation 15 kg cm torque for better results. You can also use of a simple two-link robotic 9g servo motors. arm with joints and end Next, is two 30 centimeter wooden or steel rulers effector. to make the links of the robotic arm. A drill and a few nuts and bolts are necessary to fit the wooden or steel ruler to the servo horn. An L clamp or a piece of sheet metal that can be bent into an “L” shape is needed to hold the pen or pencil using a paper clip. A few male-to male jumper wires are needed to connect the servomotors to the microcontroller. An Arduino Uno with a USB-UART cable is the microcontroller I used. A 5V 1A power supply is required to power the servomotor. 66 SERVO Issue-1.2020 A Computer- Controlled Letter Writing Robotic
Arm By V S Rajashekhar
FIGURE 2: The first servomotor is attached to ground. The ruler is connected to the horn. The second servomotor is attached to the other end.
Next, attach the L clamp to the end of the ruler so that the pen or pencil can be attached to it. Refer to
FIGURE 3: The second link of the robotic arm is made by attaching to the horn of servomotor 2. Building the Two-Link Robotic Arm
Find a big pad or a table and fix one of the servomotors to it. Attach the ruler to the servo horn using the nuts and bolts. Attach the second servomotor to the other end of the ruler. Your setup should look something like Figure 1. You’ll now need to make a similar horn and ruler setup as shown in Figure 2.
Try changing the initial angle of the mechanical robotic arms and you’ll find differences in the font style! SERVO Issue-1.2020 67 FIGURE 5: The assembled robotic arm ready to FIGURE 4: write the letters. The color pen attached to the L clamp made of Circuit Connections sheet metal. The circuit is shown in Figure 5. A breadboard This is the is used and the 5V 1A power is attached to it. From end effector. this, the power is distributed to the two servomotors. Pins 10 and 9 are given to the servomotor as 1 and 2, Figure 3. Attach the servo horn with the ruler and pen to respectively. the second servomotor. Your two-link robotic arm is ready Here, servomotor 1 is the grounded motor and and should resemble Figure 4. servomotor 2 is the motor that is attached to the link connected to servomotor 1. FIGURE 6: The circuit diagram of the robotic arm with the Finally, connect the male-to-male jumper wire from motors and microcontroller. the ground pin of the Uno to the ground in the breadboard. Software Setup and Running the Code A. Programming the Microcontroller
Open your computer and install the Arduino software. You can get it from https://www. arduino.cc/en/Main/Software. Open the Arduino file that is included with the downloads for this article. Connect the Uno to the computer and upload the code. Remember to keep the board connected to the computer until the end of the project. The following block of code tells you that the letter A will be written if the button A is pressed in the GUI (covered next): 68 SERVO Issue-1.2020 if(val == ‘a’){ //if a received myservo1.write(0); the initial position of the links, the robotic arm writes in myservo2.write(15); a different font as shown at https://youtu.be/5QB- delay(2000); lQINRKw. . . I hope you fi nd this “write” on the money for your next . computer-controlled project! SV myservo1.write(0); myservo2.write(22.5); delay(2000); To post comments on this article and fi nd } any associated fi les and/or downloads, go to www.servomagazine.com/magazine/issue/2020/01. If button A is pressed, that value is sent to the microcontroller. It makes servomotor 1 (myservo1) and servomotor 2 (myservo2) move to certain angles with a delay of two seconds in between each transition.
B. Graphical User Interface
1. Download the Processing software at https:// processing.org/download. 2. Open the fi le alpha_writer.pde that’s in the article downloads. 3. Look out for this line: port = new Serial(this, “/dev/ ttyACM0”, 9600); Replace “/dev/ttyACM0” with FIGURE 7: A GUI used for giving the input to the robotic arm. the port name to which your Arduino is connected. Don’t forget to use the double quotes. THE MOST COMPLETE PROGRAMMING TUTORIAL! 4. Run the Processing program and you should get the screen shown Everything you need to learn to program PIC® micro- in Figure 6. controllers is included in this package Success! You’re ready to write Learn the fundamental concepts of programming, letters by clicking on the button shown including program flow, loops, coding techniques, binary in the screen. manipulation, device-to-device communication, user Adjust a camera (possibly a web interface design, in-circuit debugging, and more! camera) over the robot so that you can see what it’s writing. Includes all the necessary the software, compiler, $99.99 trainer board, cable, tutorial with exercises and sample Watch the computer-controlled Academic and bulk pricing available robotic arm writing all 26 code! English letters at https://youtu. Check out our other popular products be/0612D6gnf3U. By adjusting for PIC® developers including: U2 Programmer PBP3 Compiler The more rigid the robot 3 Prototyping Boards PBP™ is, the more accurate the PICBASIC PRO Compiler Experimenter Boards www.melabs.com letters written will be! Contact us at [email protected]
SERVO Issue-1.2020 69 Connected Cars — A Fast Brewing World in Automotive There’s a saying that the cars we drive say a lot about us. I think this couldn’t be more true in the world we live in.
Somewhere in a Utopian world where each car communicates with one another. After all, communication is the key to staying connected.
e yearn for the best return on investment after-market service. As of late, buyers have also started when it comes to selecting a car. Our go- considering the safety features (airbags, ABS). This was a to parameters to shortlist cars have been result of lenient regulations on the safety requirements. Wconsistent over the years. A standard question Early adopters have added another new and very which is still very valid today is, “Mileage kitna deti hai?” or critical parameter to this checklist, which is whether the car what is the mileage? has in-built connectivity. To understand the importance of This continues to be a major deal breaker for a good these features, the late adopters need to catch up with this portion of customers, but most buyers also consider the innovative suite of connected car services or else they will size of the vehicle, expected resale value, fuel cost, and miss out on a very exciting — yet important — experience. 70 SERVO Issue-1.2020 By Abhinav Kumar To post comments on this article, go to www.servomagazine.com/magazine/issue/2020/01.
If the buzz phrase “connected car” caught your video, Internet, social media, and mobile offi ce). attention, read on. 7. Driver Assistance: These functions comprise of Let’s begin by answering what a connected car is all partially or fully automatic driving. There are in-car speech about. recognition or voice activation systems which aim to remove A connected car is a vehicle which has the ability to the distraction of looking at your mobile or car dashboards communicate with systems both inside and outside, using in- while driving (operational assistance or autopilot in heavy car connectivity. A connected car has Internet access within traffi c, in parking, or on highways). it which allows data sharing with devices (also) both inside 8. Comfort and Well-being: This manages driver’s and outside the vehicle. comfort and current state to drive (fatigue detection, In more basic terms, you’re driving a vehicle which is automatic environment adjustments to keep drivers alert, constantly sending key data points from the car to a cloud- and medical assistance). based application hosted at a secure site. Now, please don’t jump to the conclusion of your privacy being compromised It’s obvious to think at this moment that your car which is not the case here, but surely one should have doesn’t do any of this, or possesses just a few functions concerns. However, that’s a discussion for another day which but not all. This has already become a hot space to follow, will last for years to come. and automotive OEMs are racing with one another to roll Next, you want to inquire about the services which are out these functionalities in more and more models, without enabled in a connected car. limiting them to their premium ones. Typically, the following are the broad services which can So, let’s take a step back and see how this came into be activated using the connected car suite: existence. What was the infl ection point which led to its discovery? 1. Car Navigation: The features under this category General Motors was the fi rst automaker to bring the allow the driver to make informed decisions on reaching a fi rst connected car features to market with a program called destination quickly, safely, and in a cost-effi cient manner OnStar in 1996. They started this with the Cadillac DeVille, using navigation data (current traffi c information, shortest Seville, and Eldorado. routes available, and parking lot or garage assistance, In the beginning, the program was limited to eventually leading to optimized fuel consumption). notifi cations of crashes to emergency responders, locating 2. E-commerce: This could be an array of services the vehicle, and roadside assistance. While this began as an enabling users to purchase goods or services on-the-fl y. (Pay after-market model, i.e., customers can opt for these services for your fuel from your car app, order food and beverages, and choose to pay for them like they do with additional pay parking, tolls, etc.) accessories for their cars. In 1998, GM improved the OnStar 3. Vehicle Insights: These functions enable drivers to service with a change to factory-installed models that allow know the vehicle condition and further help them reduce for hands-free calling and voice recognition. operating costs and improve ease of use (vehicle condition During these years, other OEMs geared themselves — mainly referred to as telematics — and service scheduling up and launched similar suites of services. In 1999, and reminders based on the vehicle condition, remote Mercedes-Benz launched its TeleAid telematics program operations, etc.). with emergency response roadside assistance and location 4. Breakdown Prevention: This is basically predictive of stolen vehicles. By 2003, connected car services included analytics or data to analyze to predict events. In this, using vehicle health reports, turn-by-turn directions, and a network a back end algorithm predicting breakdowns and being access device. The OnStar program was such a huge success connected to a breakdown service, the car has the ability that in 2015, OnStar had processed one billion requests to use an outbound service intervening via phone, SMS, or from customers. It’s safe to consider it the benchmark push notifi cation on the connected car app. program in this space. 5. Safety: These functions intimate the driver of Clearly, this area has enough promise and has already external hazards and internal responses of the vehicle to delivered value in various ways in different parts of the hazards. Basically, in case you have had an unfortunate world. The strong, steady, and slow world of automotive has crash, your car immediately makes an emergency call been totally rocked by new technology. It defi nitely gave it (referred to as e-call) to the responsible call center and an extra pair of supersonic wings to fl y faster than ever. reports the incident (emergency breaking, lane keeping, There’s a huge ecosystem of connected car services adaptive cruise control, and blind spot object identifi cation). and mobility services startups, technology giants, consulting 6. Entertainment: This involves integrating content companies, and fi nally, automotive OEMs that are working from various sources on the entertainment unit for the tirelessly to modernize the way we commute. SV passengers (smartphone interface, Wi-Fi hotspot, music, SERVO Issue-1.2020 71 New Products Continued from page 27
1. Six operating modes: torque control; velocity control; position control; extended position control; current based position control; and PWM control. 2. Profile control for smooth motion planning. 3. Improved heatsink featuring an aluminum case. 4. Hollow back case minimizes cable stress (three-way routing). 5. Direct screw assembly to the case (without nut insert). 6. Energy saving; reduced current from 100 mA to 40 mA. 7. 28.4% reduced volume compared to the MX-106. 8. Supports synchronous control mode. ROBOTIS For further information, contact: www.robotis.com
Dual 60A Speed edge. A built-in 5V 1A switch-mode Controller BEC can supply power for your receiver or microcontroller, as well as 3-4 he Sabertooth Dual Drive Board standard analog servos. The lithium Tnow available from AndyMark is cutoff mode allows Sabertooth to acceptable for high powered robots operate safely with lithium-ion and up to 120 lbs in combat or up to lithium polymer battery packs. This 1,000 lbs for general-purpose robotics. component is not legal for the FIRST It can supply two DC brushed motors Robotics Competition and FIRST Tech with up to 60A each. Peak currents Challenge robots. Features include: of 120A per channel are achievable • Synchronous regenerative drive for a few seconds. Overcurrent and • Ultrasonic switching frequency thermal protection integrated into • Thermal and overcurrent the controller ensure you’ll never protection have to worry about killing the • Lithium protection mode driver with stalls. Dual motor control can be operated via • Two-channel 60A continuous delivery analog voltage, radio control, serial, and packetized serial. Independent speed and direction operating modes make it Specifications are: the ideal driver for tank-style robots. Price is $190. • Input: analog, R/C, simplified serial, packetized serial The operating mode is set with the onboard DIP • Voltage: 6-30V nominal, 33.6V absolute maximum switches so there are no jumpers to lose and screw terminals • Weight: 0.664 pounds for connections mean no soldering is required. This controller also has synchronous regenerative capabilities. For further information, contact: The regenerative topology means that your batteries get recharged whenever you command your robot to slow down AndyMark or reverse. Sabertooth also allows you to make very fast www.andymark.com stops and reverses, giving your robot a quick and nimble
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