Coilgun Turret

ASR Second Semester Project Paper Tinyen Shih

I. Abstract: The end goal of this project was to build a remote control coilgun turret capable of firing one-inch slugs of decapitated screws, nails, and magnets of similar sizes while being remotely aimed and fired by a remote control. This was originally going to be a coilgun mounted on a remote control car, but delays caused by finding capacitors and chargers able to produce the amount of power needed from small batteries required the project be downscaled to its present incarnation. The final coilgun is powered by a set of capacitors totaling 1.32 mF at 330V. This provides the coilgun with about 65.3 J of energy discharged over ?? seconds for a peak current of ??. With that in mind, the coilgun can consistently shoot the screw slugs several feet and with enough force to make recoil a problem. The turret itself is constructed out of Lego for several reasons: One, because I couldn’t find a better turntable with gear teeth. Two, I took my project home several times and my lack of access to SolidWorks, a 3D Printer, and time drove me to find alternatives. In the final product, the Arduino can drive with the gears with motors and can rotate the barrel in all directions and elevate it between 10 degrees and 60+ degrees from the horizontal.

Tinyen Shih Dr. Dann May 2013 ASR D Block

Table of Contents:

I. Abstract…………………………………………………………………………...1 II. Introduction…………………………………………………………………...... 1 II.I. Applications…………………………………………………………….....3 II.II. Motivation…………………………………………………………………5 II.III. History……………………………………………………………………..5 III. Theory……………………………………………………………………………..6 IV. Design……………………………………………………………………………..8 IV.I. Physical Design……………………………………………………………8 IV.II. Circuit Design……………………………………………………………10 IV.II.I. Coil Circuit……………………………………………………….10 IV.II.II. Motor Circuit……………………………………………………12 IV.II.III.Aggregate Circuit……………………………………………….13 IV.III. Radio Design……………………………………………………………..14 V. Results (incomplete)……………………………………………………………..14 VI. Acknowledgements………………………………………………………………15 VII. Bibliography……………………………………………………………………..15

Appendix A: Parts List……………………………………………………………...……16 Appendix B: Arduino Code…………………………………………………………..….17 Appendix C: Photos+ CAD Drawing: (19)

II. Introduction: This second semester project, building a remote control coilgun turret, has two parts; one, it explores the applications of electromagnetism to launch physical objects, and secondly, it delves into radio communications used in remote control toys and combines both into a miniature weapons platform.

II.I Applications: Imagine an omni-ammunition gun. One whose specifications allow it to shoot any type of ammunition, from manufactured bullets to refrigerator magnets to broken screws. Imagine a gun more silent than any other, even more quiet than those with silencers. This is the coilgun: silent, deadly, and magnetically appealing to science-fiction writers all across the world as a futuristic weapon of choice. If it makes anyone feel any better, these guns are also naturally semi-automatic, easily made fully automatic while remaining perfectly legal without a permit, easy to build, and nigh-impossible to regulate. On the other hand, the most powerful ones available to civilians right now, such as the one I built barely outclass airsoft guns [7]. Still, the potential of electromagnetic weapons is immense. Theoretically, given the development of superconductors with zero resistance, the only two factors limiting how fast a projectile can be launched are: energy storage in capacitors and relativity as the velocity approaches the speed of light. And when the projectile hits something…well, there’s a reason this is the current focus of Navy research. The fundamental principle behind such principles is that anything in the universe can be destroyed by hitting it really, really hard with something else. A projectile coming in even at some small fraction of the speed of light will still have more damaging power behind it than even nuclear weapons of the same mass. Kinetic weapons are just that powerful. [2]

Figure 1: Picture of Navy test. [6] That propellant-like plume? That’s super heated gas turned to plasma from the friction generated by the projectile passing by. The distortion in front? Air build up in front of the projectile. It’s going really, really fast.

Now imagine this…in space, where there is no air to superheat or build up. All 2 2 that energy instead going to the forward kinetic energy. Pure ½ mv and no Fair=bv . As a non-player character gunner in the video game Mass Effect 2 once stated about his weapon: “Sir Isaac Newton is the deadliest son-of-a-bitch in space!” [2]

The remote control aspect of this project is more benign, yet has some roots in darker applications, such as drones. As a democracy, we care very much for the value of each human life, and the ability to not risk American lives is one of the primary motivation behind the current airborne drone and drone spying programs. Other benefits include being able to switch out pilots easily, reducing stress on soldiers operating these war machines and making the concept of 10+ hour flights that were once common with the U2 spy planes look silly and Spartan in comparison [1]. But such systems demand

much of engineers, with much smaller fault tolerances, and I wanted to experience for myself a little of what some of those challenges were. II.II. Motivation: Upon reading aerodynamic engineer Ben Rich’s Skunk Works, describing the design process and testing of the iconic U-2 spy plane still in use today over 50 years since the first deployment, the SR-71 Blackbird that set speed records on its retirement flights, and the Nighthawk F-117 Stealth Fighter that was responsible for 20% of hits in Operation Desert Storm [1], I realized many engineers are employed by the defense industry. As an aspiring engineer myself, this is a very real reality in the job marketplace, and so I wanted to try out making a small-scale weapon to see how it felt. More directly related, however, is that the United States military is also testing numerous electromagnetic weapons systems. One such system of railgun launches hunks of metal at Mach 8 speeds, resulting in damage approximating that of a cruise missile. However, since the projectiles are hunks of metal, they are far cheaper to produce and store allowing battleships to pack a hundred times more firepower using the same capacity as compared to now. [5] I also wanted to incorporate as much as I learned throughout the year in ASR and Physics C last year into this project. Building a coilgun turret hit many of them, such as the electromagnetism used in the motor project, the radio communications used in the weather balloon project, and the Newtonian physics and electricity/magnetism learned last year. I intended this project to be able to follow orders from a remote control to aim right, left, up, down, and fire metal projectiles at reasonable speed, maybe enough to puncture empty soda cans or at least knock them over. The coilgun itself was to be a single stage (one coil) only, with the projectile getting drawn from behind the coil into the coil, where upon the coil is turned off, allowing the projectile to emerge forth. II.III. History In 1819, Hans Christian Orsted of Copenhagnen noticed, much to his confusion, that compass needles were being deflected when there was current traveling through nearby wires. Within two years, Ampere had developed his theory of “electrodynamics” through experimental procedure while Simeon Denis Poisson explored the first

approximations of magnetization. Michael Faraday and Joseph Henry each finally discovered electromagnetic induction in 1835 independently, one of the primary principles upon which the coilgun portion of this project depends on. From here, modern electromagnetism was born, forming many of the foundations of the industrialized world such as motors. [3] Coilguns were first made practical in the 1960s, when science research accelerated into overdrive and finally created electrical components capable of handling the large currents involved. [8] On the other hand, automated and remote control systems are not new at all. Greek Mythology has references to a metal automaton, named Talos, who would launch rocks at enemies from the sea much like artillery emplacements, but autonomously, much like this project in remotely launching projectiles. From the view of military planners, purely kinetic weapons such as coilguns are also easier to predict, resulting in less collateral damage and civilian casualties, which is why many American missiles are essentially guided blocks of concrete [2]. As a result, such limitations aren’t stopping the Navy, who plan to equip warships with 64 MJ railguns, which work similarly to coilguns in needing a large amount of current and also using magnetism to launch projectiles or even planes at high speed. [2] These hunks of metal, launched at Mach 8, do about the same amount of damage as a cruise missile, but are lower maintenance than cruise missiles while allowing warships to carry a hundred of them in the space it takes to ship one cruise missile.

III. Theory: Coilguns operate by using the principles of electromagnetism. As Hans Christen Orsted discovered, a wire carrying current creates a magnetic field around itself. When the wire is bent into loops, the magnetic field lines then approximate that of a bar magnet when current is running through. Magnets, permanent or created from such configurations of wire, induce magnetism in ferromagnetic materials such as the steel projectiles used in this project. The original magnetic field and the induced one The coil actually accelerating the projectile does so on the principles of electromagnetism. The projectile needs to be ferromagnetic so that when the sudden spike in current from the capacitors happens, the magnetic field produced by the coil, or

flux, changes, exerts a force on the projectile, causing it to accelerate toward the center of the coil. The magnetic field exerted is described by the equation: B = µ0nI where B is magnetic field, n is the number of loops the coil has, and I is the current flowing through the coil, which is actually changing. The I in the equation is why using capacitors to generate a massive amount of current is important; so enough of a magnetic field can be generated to magnetize the projectile so it exerts a huge force against the current in the coil and goes forward. [3] Take for example the 300V that is charging the capacitors discharging through the 6ohm coil with 1000 turns. I=300V/6 ohms = 50A, so B = (4π *10−7 Tm / A)(1000)(50A) = .06Tm . I currently don’t know how many turns of wire I have, so there are no theoretical calculations of the magnetic field. Even when the current runs out, the projectile is already moving and shoots out of the barrel. One of the factors I identified to accelerating projectiles to high speed was the release of energy from the capacitors. Since the energy coming out of capacitors is ½CV2 [4], I wanted the voltage available to be as high as possible. This was done by taking disposable camera circuits, which already take 1.5V to 330V to charge a capacitor and then release that energy through the flash, and cutting out the part that boosts the voltage, short-circuiting the wires that are usually connected when the “charge” button on the disposable camera is pressed, and reattaching the battery and charging circuit where the capacitor used to be. Using this, I had an instant 300V source given a 1.5V battery and could charge the pile of 330V capacitors cut out from the cameras. The voltage booster itself works through a transformer, which is essentially two coils of wire with different numbers of turns enmeshed with each other. By inducing an AC current, done in this circuit by turning on and off the current coming from the battery to look like: _Π_ Π_ over time, the changing magnetic field in the first coil, the primary, induces a reverse magnetic field in the secondary coil. However, the second coil typically has fewer turns, so each turn gets a larger voltage to compensate. All this induces the second coil have an output sine wave of voltage, which at its peak has a much larger voltage difference than the first. By cutting that wave in half with a diode, the resulting voltage difference is still much larger and allows my charging circuit to achieve 300V from 1.5V and charge up the more powerful capacitors the turret uses.

The limiting thing here was the amount of charge that the voltage booster could output. Designed to charge just one such capacitor in a few seconds, the voltage booster could take over a minute to charge the capacitors enough to fire a decent shot. Another disadvantage was whichever unlucky 1.5V battery was plugged in was drained really quickly. Fortunately, I had plenty of 1.5V batteries from the other disposable cameras such that it wasn’t a problem. Heat was not a problem in this case since the astronomical current is released for a tiny fraction of a second and does did not noticeably heat up any components of the circuit. So in the end, I decided to use the modified camera circuits, which took 1.5V AA batteries and boosted their voltage to over 300V to charge 330V capacitors. The result, for the old 16V capacitors to the new, was a four hundred-fold increase in energy simply based on voltage.

IV. Design: Theoretically, given a coil and a projectile that fits within the coil, the projectile could be accelerated any speed because the magnetic field of the coil is dependent only on the current going through the coil; there are no construction limitations. However, in practice, this is limited by the coil overheating, which changes the resistance of the coil and thus the amount of current going through to limit magnetic field strength. The amount of time it takes to charge up capacitors is also a practical concern, and finally the inductance of the coil itself. IV.I. Physical Construction Most of the structure of the turret is made from the very-adaptable Lego pieces. This came about after a few weeks of imagining the coil gun strapped atop a remote control vehicle and then realizing that there needed to be some way to aim the gun. The solution to this, of course, was a turntable, which would allow me to route wires through the hollow center and not worry about them getting tangled and impeding the horizontal movement of the gun. The first one I got my hands on was a Lego version, and so from there, it was a logical jump to making the entire gearing system out of Legos and later the entire structure.

So while the turntable and motor connected to it in a gear train control the horizontal movement, the other motor, connected to a gearbox, controls the vertical movement of the barrel. The gearbox itself has a worm gear meshed with a 24-tooth clutch gear. This combination gears down the motor, allowing for slower movement, something greatly appreciated by operators when the entire range of movement for the arm is less than a half-rotation, and strengthens the output torque, allowing the motor to lift heavier barrels and projectiles. The clutch gear is also one of the more interesting features of this design. It works like a regular gear until too much force is exerted against it, at which it center, where the axle goes through slips against the rest of the gear. This is useful for not stalling the motor should that arm become trapped against something like a corner of the turret structure. In that case, the middle of the gear would continue turning, but the arm won’t move and wrench apart the turret. Another feature of the design is the hybridizations of two very different philosophies in Lego. One is best represented in the yellow gearbox that features the traditional stud-tube connection system that the iconic bricks use, while the other may be symbolized by the turntable using a newer beam-pin system more commonly seen in today’s Lego Technic systems. I found the latter useful for strength, hence lots of cross bracing and making up most of the structure, but, for the former, bricks were simpler to customize, which is why it makes up the motor housings. The old standby, tape, was used to secure motors and modify spacing to reduce play between gears, preventing motors from pushing themselves away. The coil, the most important part of the project, is constructed out of an In N-Out Burger fast food drinking straw and recycled magnetic wire from a first-semester motor project electromagnet. It is 28.92mm in length and 3.31mm thick from straw to outer layer, while the wire used is .38mm thick, meaning there are about 700 turns in the coil. This part was originally going to be made from a small, PVC pipe, but a straw proved able to handle the stresses and get the magnetic wire closer to the projectiles while being more lightweight and easy to modify. This all reduced stress on the already- heavy turntable and greatly enhanced performance compared to the original test coil

made from a regular spool of wire. Besides, that spool of wire wouldn’t have fit on the turntable anyway. Currently, this turret has fired three different types of projectiles. The largest type, is about 30mm long and cut from rods and screws with a hacksaw for a nice clean cut and smoothed with sand paper. The second type is sawed off nails brought from home. These come pre-sharpened and don’t lose as much energy to rubbing against the sides of the barrel. Third are permanent neodymium magnets. Bought by fellow coilgun-maker Conor Shanley, these are the smallest projectiles that have been tested, and they take off like rockets. All are loaded through the front of the barrel like a cannon and end up slightly behind the coil, supported by a wooden rod that is taped onto the back. When the current is turned on in the coil, the projectile is drawn forward by the burst of magnetic field, and by the time the current runs out, it is already on its way out of the barrel. Finally, the joystick was planned initially, but then dropped as time constraints forced the remote control out of the design, and then returned as a version wired directly to the analog ports of the Arduino. Using a joystick design from an old Lego Mindstorms project book, the design was adapted it so that a wire at 5V from the Arduino could be wrapped around that joystick. Next, metal plates were affixed (cut out from remains of battery holders in disposable cameras and connected to the analog ports of the Arduino) to four bricks surrounding the joystick. When a user tipped the joystick, the high voltage wire contacted one of the metal plates, causing the Arduino to detect high voltage from one of the analog pins and act accordingly. A similar system would be been built for firing the coil, but there wasn’t time.

IV.II. Electric Circuit Design The circuit in this project had to do three things: charge capacitors, discharge those capacitors through a coil, operate two motors to aim the coil, and communicate with a radio transmitter. IV.II.I. Coil Circuit Probably the most important part of the circuit, the charging of capacitors and discharging them through the coil, was at first done with transistors to switch the

capacitors onto a circuit with the coil, but while this worked with the original 16V capacitors that were first used, it utterly failed with the more powerful 330V capacitors as the massive voltage difference forced its way through the transistor anyway. Hence, a relay was added in between.

Figure 2: Subcircuit of coilgun firing mechanism. As one can see, the relay switches the capacitor bank between being charged by the 300V camera circuit and being discharged through the coil. All it needs is a signal from the Arduino to trigger it the short, giant burst of current through the coil. The voltage booster, seen on the left side of the diagram, is rigged out of pieces of disposable camera, was probably the most difficult part of this project. As mentioned before, it takes the 1.5V of a battery and takes it up to 330V. Even with the help of the internet, it was difficult to figure out how exactly they did that, and even then only allowed me to convert two circuits into voltage boosters. On the other hand, all those boards did provide me with many capacitors. The total capacitance, as the capacitors were all in series, was: 7*120uF +3*160uF = 1320uF. 1 1 Thus the energy stored is E = CV 2 = (1320 *10−6 F)(330V )2 = 71.874J 2 2 I originally imagined using 4700uF capacitors easily found in the ASR room, but those only went up to 16V. To highlight the improvement in performance and partially

justify the time I spent building voltage boosters, I would like to point out that since each 1 1 16V 4700uF capacitor provides: E = CV 2 = (4700 *10−6 F)(16V )2 = .602J 2 2 71.874J I would have needed: = 120 16V capacitors to match the same energy storage. .602J Not bad for free, drugstore counter stuff! Even the battery needs weren’t bad; with the coil portion of the circuit needed a 1.5V AA battery to run charge the capacitors while the relay needed a 9V battery. In contrast, using powerful batteries instead of capacitors to provide current through the coil would have increased weight, which was a problem back when the gun was to be mounted on a remote control vehicle. In addition, the internal resistance of the batteries would have severely limited current. Because there is almost no resistance in the coil or capacitors, the internal resistance of the batteries and charger are what limited charging speed in this circuit.

IV.II.II. Motor Circuits Each motor circuit needed to do three things: turn the motor clockwise, turn the motor counter-clockwise, and turn it off. To accomplish this, two Arduino pins were used: one to turn the motor on and off, and the other to set direction.

Figure 3: Motor Control Circuit. As one can see, the pin controlling the transistor controlling the switches flips the voltage difference across the motor, allowing it to turn either way while the second Arduino pin connects the relay switches to ground, determining if the motor moves at all. Because there were two motors, this controller had to be constructed two times to accomadate both. All of this was powered by the same 9V battery mentioned earlier.

IV.II.III. Aggregate Turret Circuit

Figure 4: Entire circuit devoted to operation and aiming of coilgun. IV.III. Radio Communications As of now, there are no radio communications and everything is still speculation, but I plan on using the NTX and NRX system, identical to the one used in the weather balloon project, to facilitate communications between the remote control Arduino and the turret Arduino.

V. Results Average Time taken to charge bank to 300V in 3 trials: Muzzle velocity was measured by connecting a Labquest to a photogate, placing the photogate in front of the barrel, firing the coilgun, measuring the blocked/unblocked times, and finally dividing the difference by the length of the projectile. Trial 1 Trial 2 Trial 3 Average Screw Projectile Nail Projectile Magnet Projectile

VI. Acknowledgements I would like to thank Dr. Dann for teaching me these last two years and for his boundless energy for all things Maker. Mr. Del Carlo, was also instrumental in this project, making recommendations on what tools to use to bring my ideas to reality. Conor Shanley, who was doing a staged coilgun and was a good person to bounce ideas off of. Guy running film processing counter in downtown, for dealing with an annoying ratty teenager asking for things that could get himself killed. Matti de los Reyes and John Welch for when I got frustrated with my own project and needed a distraction. You guys were just the closest people. Micah Rosales for fulfilling the above and having his excellent paper online as a model for this one. Thank you all.

VII. Bibliography [1] Rich, Ben. Skunk Works, Back Ray Books, 1994 [2] http://tvtropes.org/pmwiki/pmwiki.php/Main/MagneticWeapons [3] https://en.wikipedia.org/wiki/Electromagnetism [4] Hewitt, Paul. Conceptual Physics 10th edition, Pearson, 2006 [5] http://en.wikipedia.org/wiki/Coilgun [6] http://en.wikipedia.org/wiki/Railgun [7] http://www.instructables.com/id/Coilgun-Handgun/ [8] http://en.wikipedia.org/wiki/Electromagnetic_propulsion

Appendix A: Parts List Coil wire: ASR Room, free as recycled from electromagnet from first semester 3 NPN Power transistor: ASR Room: for relay operation 2 NPN transistors: ASR Room: turn on and off motors 3 Relays: Radioshack: These were recycled from my motor in the first semester and serve, just as they did then, as direction control of current, this time for motors 7 120uF 330V disposable camera photoflash capacitors 3 160uF 330V disposable camera photorflash capacitors 2 Disposable Camera voltage boosters (free as used from drugstore) 1 Arduino + Radio Receiver: Need to find out remote frequencies: ASR Room Various jumper wires: ASR Room 2 small DC motors: to aim barrel 2 8t Lego gears epoxied on to allow motors to operate gears 1 Lego turntable: for aiming of coil gun in horizontal direction 1 Lego gearbox: for elevating and lowering coilgun. This includes: 1 24t clutch gear: to ensure elevation motor does not stall under heavy loads 1 worm gear: meshed with 24t to slow down rotation from fast motor. 1 AA Battery for coilgun power: free, since disposable cameras come with them 2 9V Batteries: one for operation of relays, other for Arduino. Structure of turret: Lego Pieces: mostly for structural support Pulley band: “shock absorber” for direction motor

And since I keep coming back to these: 15 Disposable Cameras: Free at drugstores that still process disposable cameras (getting rather rare with the rise of digital cameras). I just asked and they gave me as many as I wanted out of the waste bin without film. If one is willing to buy them, they are slightly more widely available at more drugstores and are $7 for two of them. All of my voltage boosting circuits, batteries, and capacitors came from here. I took these unloved and unwanted poor little things and tore them apart, using their entrails and brains for my project. *evil laugh*

Appendix B: Turret Arduino Code: What’s here just raises an lowers the barrel by itself without any input, but the methods for firing and aiming of barrel are all here: const int Elevation = 5; const int ElevationPower = 3; const int buttonUp = 0; const int buttonDown = 3; const int Direction = 10; const int DirectionPower = 9; const int buttonRight = 1; const int buttonLeft = 2; const int Coil = 11; const int coilButton = 4;

//setting up pin numbers so I don’t have to go through the entire program and change every number if I need to change pin numbers void setup() { pinMode(Elevation, OUTPUT); pinMode(ElevationPower, OUTPUT);

pinMode(Direction, OUTPUT); pinMode(DirectionPower, OUTPUT);

pinMode(Coil, OUTPUT); } void loop() //So the main program checks analog pins 0-4 for high voltage. When one is detected, it turns on the corresponding motor in the corresponding direction. If no pin is detected with high voltage, the program shuts down the motors. This happens over and over again. { if(analogRead(buttonUp) > 1022) { aimUp(); } else if(analogRead(buttonDown)>1022) { aimDown(); } else {

elevationOff(); } if(analogRead(buttonRight)> 1022) { aimRight(); } else if(analogRead(buttonLeft)> 1022) { aimLeft(); } else { directionOff(); } if(analogRead(coilButton)> 1022) { FIRE(); } } void aimUp() { digitalWrite(Elevation, LOW); digitalWrite(ElevationPower, HIGH); } void aimDown() { digitalWrite(Elevation, HIGH); digitalWrite(ElevationPower, HIGH); } void elevationOff() { digitalWrite(ElevationPower, LOW); digitalWrite(Elevation, LOW); } void aimRight() { digitalWrite(Direction, LOW); digitalWrite(DirectionPower, HIGH); } void aimLeft() { digitalWrite(Direction, HIGH);

digitalWrite(DirectionPower, HIGH); } void directionOff() { digitalWrite(DirectionPower, LOW); digitalWrite(Direction, LOW); } void FIRE() { digitalWrite(Coil, HIGH); delay(10); //This delay had to be changed several times so that the projectile was not pulled back into the coil by the residual current after it had crossed the midpoint of the coil. digitalWrite(Coil, LOW); delay(1000); //This delay is here because the main program loops over and over again really quickly. If this weren’t here, the Arduino would, at first seeing the coilButton pressed, open fire, but keep it open because the program has already looped around and still sees the slow human hand pressing the button, thus keeping the coilgun firing and resulting in the projectile getting pulled back in as described above. } Appendix C: Photos of Turret N/A