A BIOLOGICALLY INSPIRED ROBOT FOR

LUNAR EXPLORATION AND REGOLITH

EXCAVATION

by

PHILIP ALAN DUNKER

Submitted in partial fulfillment of the requirements

For the degree of Master of Science in Engineering

Thesis Adviser: Dr. Roger Quinn

Department of Mechanical and Aerospace Engineering

CASE WESTERN RESERVE UNIVERSITY

January, 2009 CASE WESTERN RESERVE UNIVERSITY

SCHOOL OF GRADUATE STUDIES

We hereby approve the thesis/dissertation of

______

candidate for the ______degree *.

(signed)______(chair of the committee)

______

______

______

______

______

(date) ______

*We also certify that written approval has been obtained for any proprietary material contained therein. To my father, for clarity amid uncertainty.

In te, Domine, speravi;

non confundar in æternum. Table of Contents

Table of Contents ...... i

List of Tables ...... iv

List of Figures ...... vi

Acknowledgments ...... ix

1 Introduction ...... 1

1.1 In Situ Resource Utilization (ISRU) ...... 2

1.2 Document overview ...... 3

2 Background ...... 5

2.1 Lunar and Martian rovers ...... 5

2.2 Reduced-actuation legged robots ...... 9

2.2.1 Whegs™ robots ...... 12

2.3 Lessons learned from Whegs™ II ...... 16

3 Design and Fabrication of Lunar Whegs™ ...... 18

3.1 Chassis ...... 19

3.2 Torsion devices ...... 20

i

3.3 Body joint ...... 22

3.3.1 Initial design ...... 22

3.3.2 Torque requirement testing ...... 27

3.4 Steering ...... 32

3.5 Drive train ...... 33

3.6 Foot design ...... 35

3.7 Modeling and fabrication ...... 38

4 Mission Tasks ...... 39

4.1 Robotic excavation teams ...... 39

4.2 Autonomy ...... 41

4.3 Electronics and wiring ...... 43

4.4 Actuated regolith scoop ...... 44

5 Robot Performance ...... 48

5.1 Performance specifications ...... 48

5.2 Autonomy ...... 49

5.3 Mars Yard testing ...... 49

5.4 Sandbox testing ...... 50

5.5 Obstacle climbing ...... 52

6 Conclusions and Future Work ...... 55

6.1 Conclusions ...... 55

6.2 Future work ...... 55

Appendix A : Body Joint Servo Testing ...... 57

A.1 Setup ...... 57

A.2 Procedure ...... 58

A.3 Results ...... 58

Appendix B : Mechanical Drawings ...... 61

Appendix C : Selected Design Calculations ...... 62

ii

Appendix D : Bill of Materials ...... 66

References ...... 69

iii

List of Tables

Table 2.1: Comparison of some parameters of the different rover designs ...... 8

Table 2.2: Power-to-mass analysis of selected robots ...... 15

Table 3.1: Sprocket ratios, joint ranges, torques for varying configurations of the body joint transmission. These values assume a servo with an initial range of ±90°...... 30

Table 4.1: Requirements for basic life-sustaining resources for one person (Tchobanoglous and Schroeder 1987) ...... 40

Table 4.2: Performance comparison between a loader attachment for a human rover and an autonomous robotic excavation team...... 41

Table 5.1: Comparison of performance of Whegs™ II and Lunar Whegs™ ...... 48

Table 5.2: Performance in sandbox ...... 51

Table 5.3: Comparison of some Whegs™ II and Lunar Whegs™ parameters relevant to obstacle climbing ...... 53

Table A.1: Test results for servos at varying voltages and load ...... 59

iv

Table A.2: Available body joint torque for different transmission ratios, voltages, and load ...... 59

v

List of Figures

Figure 1.1: Lunar Whegs™ in an artist’s enhanced environment ...... 4

Figure 2.1: Lunokhod 1(1970) ...... 6

Figure 2.2: Lunar Roving Vehicle (1971) ...... 7

Figure 2.3: Microrover Flight Experiment (Pathfinder, 1996) ...... 7

Figure 2.4: Mars Exploration Rover (2004) ...... 8

Figure 2.5: NASA's Cratos prototype ascending a moderate slope rock pile ...... 9

Figure 2.6: PROLERO, a prototype rover designed by the ESA ...... 11

Figure 2.7: Early prototype of RHex, a hexapod robot ...... 12

Figure 2.8: Whegs™ II negotiating a rubble pile ...... 12

Figure 2.9: DAGSI Whegs™ ...... 14

Figure 2.10: Whegs™ II tie rod steering arrangement ...... 17

Figure 3.1: Schematic of Lunar Whegs™ showing main robot systems ...... 19

Figure 3.2: Torsion device for Lunar Whegs™ shown in exploded (left) and assembled (right) views...... 21 vi

Figure 3.3: Initial design of body flexion joint, showing sprocket mounting (left) and compliant seal (right) ...... 24

Figure 3.4: Final design of body flexion joint ...... 24

Figure 3.5: Body joint: Exploded view (left) and assembled view (right). The joint shown is for the right side of the robot; the bearing on the left side is a mirror image...... 25

Figure 3.6: Spider coupling in series with body joint servo output ...... 26

Figure 3.7: The initial method of torque transmission to the body joint, showing cantilevered servo output sprocket ...... 27

Figure 3.8: Position feedback for the body joint servo is accomplished using a potentiometer geared to the servo output...... 30

Figure 3.9: Body joint view showing the servo shaft bearings and the method of servo capture ...... 31

Figure 3.10: Steering for Lunar Whegs™: rack-and-pinion mechanism (left) and body pass-through (right) ...... 33

Figure 3.11: Two wheel-leg prototypes for Lunar Whegs™: articulated ankle (left) and rigid (right) ...... 36

Figure 3.12: Comparison of sand performance between Whegs™ II feet and prototype feet with articulated ankle ...... 37

Figure 3.13: Fabricated rigid wheel-leg ...... 37

Figure 4.1: Proposed configuration for autonomous robotic excavation teams ...... 40

Figure 4.2: Hokuyo URG mini-LIDAR unit mounted to the front of Lunar Whegs™ ...... 42

Figure 4.3: Screen capture of obstacle avoidance algorithm. The blue arcs represent sensed distance, the red line and green line (hidden by blue) show the angular limits of the sensor, and the magenta line shows the selected heading...... 43

Figure 4.4: Inside of electronics box ...... 44

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Figure 4.5: Exploded view of scoop assembly, showing spider coupling, torsion spring, and gearbox ...... 45

Figure 4.6: Actuated scoop, showing extreme positions in range of motion: stored (left) and scooping (right) ...... 46

Figure 4.7: Different dumping options for Lunar Whegs™: flat terrain (left) and a specially designed step (right). Scoop is shown in red...... 46

Figure 5.1: Images of Lunar Whegs™ at the Mars yard at the Canadian Space Agency (PTMSS 2008 conference) in Montreal ...... 50

Figure 5.2: Lunar Whegs™ in testing sandbox ...... 51

Figure 5.3: Images showing successful climb of 5” obstacle ...... 52

Figure 5.4: Images showing successful climb of 6” obstacle ...... 52

Figure 5.5: Unsuccessful climb of 7” obstacle ...... 53

Figure A.1: Setup for servo torque test ...... 57

Figure C.1: Portion of Lunar Whegs™ front end used for calculating mass, with mass centroid and principal axes of inertia shown...... 65

viii

Acknowledgments

I would like to thank, first, all of the students and researchers in the Biologically

Inspired Robotics Laboratory, who provided technical help debugging temperamental

robot systems as well as the occasional sanity check.

Many thanks go to Alex Hunt, who was responsible for all of the CNC programming

and milling and who has done all of the design and fabrication work for the actuated

scoop. Bill Lewinger brought a great deal of robotics experience to the table and was the

one who actually made the robot move. Dr. Roger Quinn, my advisor, provided critical

direction and steered me away from dead ends.

Thanks especially to Dr. Joseph Mansour and Dr. Joseph Prahl for serving on my

thesis committee, and to John Caruso and Mike Krasowski, our NASA Glenn collaborators.

Finally, I would like to thank my mom and dad and my brother Carl for their

support and guidance, which was always appreciated much more than they realized.

This research was funded by a grant from NASA Glenn Research Center, contract

#CON103300.

ix

A Biologically Inspired Robot for Lunar Exploration and Regolith Excavation

Abstract

by

PHILIP ALAN DUNKER

In order for a long-term lunar base to be successful, resources must be gathered from its surroundings (in situ resource utilization). One of the most important resources for any human space mission is oxygen, which can be extracted from regolith on the lunar surface. The purpose of this research was to design, fabricate, and test a robot prototype for a lunar rover that would be able to explore the surface of the Moon, excavate a quantity of lunar regolith, and transport the regolith to a central oxygen extraction station. The cockroach-inspired Whegs™ robotic platform, which combines wheeled and legged locomotion using six three-spoked "wheel-leg" appendages, is well-suited for negotiating the rocky obstacles and loose material on the lunar surface. A new prototype robot was designed and constructed based upon the Whegs™ platform, and its performance on loose substrates was quantified.

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1 Introduction

Robots, and machines in general, can perform tasks that humans cannot do or else

would prefer not to do. This is one of the biggest reasons why research in robotics is not

only interesting but also functionally viable. In this sense, robots have taken over

functions which animals had previously provided. Whereas animals served as a means of

transportation and hauled loads a hundred years ago, those same functions are now performed by machines or even robots. Yet some of the tasks which remain difficult for robots are performed on a regular basis by animals, such as locomotion over irregular

terrain, and it is for this reason that roboticists look to biology for solutions to these

problems.

Because robotic legged locomotion is a promising and demonstrated solution to

negotiating uneven terrain, it makes sense to investigate its viability in a number of

challenging or hazardous situations. Robots have already been used in interplanetary 1

missions, functioning as manually operated or semi-autonomous rovers without a human

presence. As the number of astronauts in a lunar or Martian base increases, and as the

duration of the stay lengthens, robots become more feasible for performing mundane or

dangerous tasks such as resource collection, scouting, scientific sensing missions, or

moving regolith. The more able these robots are at functioning autonomously and traversing difficult terrain, and the greater their power-to-weight ratio, the more useful they will become for interplanetary bases.

1.1 In Situ Resource Utilization (ISRU)

For a human settlement to be sustainable, no matter the location, it needs an adequate supply of basic resources. Terrestrial settlers must find a source of food, water, and fuel; for space and planetary missions, the list grows to include oxygen.

Extraterrestrial settlements, such as the planned long-term lunar colony, need an ongoing supply of these resources, but the cost to ferry them regularly from Earth is very high. As a result, the In-Situ Resource Utilization project is attempting to mitigate this problem by harvesting as much of these resources as possible from the surrounding lunar environment. The lunar regolith, the material on the surface of the moon above the bedrock, which has been ejected by meteorites, can provide quantities of oxygen, hydrogen, and possibly water (Heiken, Vaniman et al. 1991). It is believed that approximately 2 m3 of regolith would be sufficient to support the needs of the proposed lunar base and astronaut crew for 24 hours. 2

This regolith could be collected in a number of ways. Human teams could be sent out

with essentially a shovel and a bucket, but this would be an unwelcome distraction from

mission-important tasks. Alternatively, a robot or a team of robots could perform the task autonomously, organizing sorties, collecting regolith, and transporting it back to the base

for processing. In addition to performing this main task, the robots could also serve as

robotic geologists or communications relays, or they could be outfitted with bulldozer-

type equipment to build protective berms around rocket launch sites. Teams of robots

would also have a greater degree of redundancy than one large piece of excavation

equipment would have.

1.2 Document overview

The purpose of this work was to design, fabricate, and test a biologically inspired

proof-of-concept lunar rover which would be able to traverse the moon autonomously

and would be suitable for regolith excavation and transportation. The result was Lunar

Whegs™ (shown in Figure 1.1), a Whegs™ robot with a sealed chassis, sand-adapted feet, autonomy capabilities, and increased payload capacity for regolith collection and towing.

3

Figure 1.1: Lunar Whegs™ in an artist’s enhanced environment

Chapter 2 of this work describes previous work in Lunar and Martian rovers, in

reduced-actuation legged locomotion, and some of the lessons learned from the robotic

predecessors of Lunar Whegs™. Chapter 3 details the overall design consideration and fabrication of Lunar Whegs™, while Chapter 4 discusses mission-specific analysis, design, and construction for lunar-type functions. Chapter 5 then shows the results and the performance of the completed robot. Finally, Chapter 6 looks at some of the conclusions that can be drawn from this research and a few of the new directions in which future work could proceed.

4

2 Background

2.1 Lunar and Martian rovers

A number of rovers have been designed and prototyped, but only four different rover designs have operated on an extraterrestrial body: two on the Moon and two on Mars. All four use all wheel drive with individual electric motors driving each of the wheels, which are specialized for the Lunar or Martian surface.

The first rover to land on an extraterrestrial body was the Lunokhod (Луноход,

“moon-walker”) rover built by the USSR. Lunokhod 1 landed on the moon in 1970 and traveled 10.47 km, having a top speed of 2.2 m/s; Lunokhod 2 (top speed 5.5 m/s) landed in 1973 and traveled 37.5 km. The Lunokhod design had eight wheels which were independently suspended; turning was accomplished by skid-steering. The rover had

5

wheels with spokes, a mesh rim, and finlike treads attached to the outside of the wheel

rim (Kemurdjian 1991; Kemurdjian 1998).

Figure 2.1: Lunokhod 1(1970)

The Lunar Roving Vehicle flew to the moon on Apollo 15, 16, and 17, operating for a total of 4 hours 26 minutes and driving 35.9 km on the Apollo 17 mission. Its primary purpose was to transport a human crew across the surface of the moon, and as a result it looked and behaved to a large extent like a terrestrial vehicle. All four wheels steered together, but with the option of decoupling and steering with the front wheels only. The

LRV drove on non-pneumatic tires. These had a thin wire mesh made of piano wire, with

a chevron tread that covered 50% of the surface contact area for increased traction. The

tire had a bump stop or inner frame which provided a hard covering for the wheel hub.

LRV rovers were capable of a top speed of 13 km/h.

6

Figure 2.2: Lunar Roving Vehicle (1971)

Figure 2.3: Microrover Flight Experiment (Pathfinder, 1996)

The 1996 Microrover (Mars Pathfinder mission, Microrover Flight Experiment,

MFEX, Figure 2.3) and the 2004 Mars Exploration Rover (MER, Figure 2.4) both use cleated wheels suspended on a “rocker-bogie” suspension which allows the rover to climb over obstacles and irregular terrain while passively keeping the wheels in contact with the ground (1996; Stone 1996; Harrington and Voorhees 2004). This mechanism has been

7

successful in keeping the rovers upright and drivable. However, due to the

communication lag between Earth and Mars, they are relatively slow. MFEX had a top

speed of 0.67 cm/s; the MER top speed is 5 cm/s. Table 2.1 shows some key parameters of each of these rover designs.

Figure 2.4: Mars Exploration Rover (2004)

Mass Length Top Speed Top Speed Wheel Diameter (kg) (m) (m/s) (bl/s) (cm) Lunokhod 1 2.2 1.0 756 2.2 51 Lunokhod 2 5.5 2.5 LRV 210 3.1 3.6 1.2 82 MFEX 10.5 0.68 0.067 0.10 13 MER 180 1.6 0.02 0.013 25

Table 2.1: Comparison of some parameters of the different rover designs

A number of prototype rovers have been designed since the first Lunokhod landing,

far more than the scope of this chapter permits enumerating. One of the more relevant

8

rover designs, however, is the NASA Cratos rover, developed in conjunction with the

ISRU initiative for lunar operation (Caruso, Abel et al. 2007). Cratos is a two-tracked

robot with a mass of 80 kg and a body length of 85 cm, having a top speed of 5 cm/s.

Because it has a low center of gravity, it is able to climb slopes with loose surface material.

The current design includes a hauling container which can hold 0.028 m3 of material and

can dump it out after transporting it. Section 4.1 below discusses the implementation of a

Cratos-type vehicle in heterogeneous robotic teams for regolith collection purposes.

Figure 2.5: NASA's Cratos prototype ascending a moderate slope rock pile

2.2 Reduced-actuation legged robots

While wheeled vehicles can be very stable and fast on flat surfaces, they encounter

problems on irregular terrain, and in the case of the two Mars rovers, the irregularities

end up requiring more complex suspensions and limiting the maximum speed of the

rover. Biological examples suggest that legged robots, like their animal counterparts, may

9

be able to negotiate irregular terrain more adeptly using legs. However, the advantage

over wheels gained by robotic legs is always tempered by the added complexity of the legs

as well as the increased weight of actuators needed to drive the independent degrees of

freedom on a robot. While terrestrial applications for legged robots may be able to

tolerate increased weight and deal with a higher number of articulated joints, mass is

always a critical constraint on space missions. Designs which maximize the power-to- weight ratio of the robot are preferable. Additionally, lunar regolith is highly abrasive and

very fine, which means that every actuated joint exposed to the regolith is a potential

failure point and needs to be tightly sealed against dust and grit.

Because of the liabilities of fully actuated legs, reduced-actuation legged robots may

be a better way to design a planetary rover that can traverse irregular terrain and deal

with obstacles while maintaining a favorable power-to-weight ratio. Such a robot would

also be able to keep a high degree of mobility without the need to introduce failure points.

The advantages of reduced-actuation legs were recognized in the construction of

PROLERO (1996), a prototype hexapod Mars rover designed by the European Space

Agency (Martin-Alvarez, Peuter et al. 1996). It was recognized that in soft substrates, rolling wheels run into compaction resistance, which is resistance arising from the wheel pressing into the material building up in front of it. This resistance counteracts the

traction gained by the rest of the wheels. Legs, on the other hand, acquire a foothold, push

off from the foothold, and then lift their foot out of the foothold, so they experience little

10

compaction resistance. As a result, PROLERO used six individually actuated L-shaped

legs operating in a wave gait to propel the robot forward. It was also capable of operating

in a tripod gait. The robot rotated its legs at a relatively constant speed and it would drop

its body onto the substrate cyclically.

Figure 2.6: PROLERO, a prototype rover designed by the ESA

A robot with a similar design is RHex (Saranli, Buehler et al. 2001), a hexapod robot

with individually actuated compliant legs. Unlike PROLERO, RHex’s designers used biological inspiration and it can walk in a tripod gait by altering the acceleration and deceleration of each leg in a defined swing-stance pattern. The height of its body is relatively constant as it runs. It uses curved legs to achieve a degree of radial compliance while walking. In addition, it has been outfitted with a fully sealed body.

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Figure 2.7: Early prototype of RHex, a hexapod robot

2.2.1 Whegs™ robots

Figure 2.8: Whegs™ II negotiating a rubble pile

As a continuation of the trend to reduce the number of actuators on a robot, the

Whegs™ concept was developed (Quinn, Nelson et al. 2001). The initial goal of Whegs™ was to provide the primary advantages of legged locomotion while using only one drive motor. In order to achieve this, Whegs™ I was designed and fabricated with one drive motor driving three separate axles. Each axle was linked to two three-spoked appendages

12

called wheel-legs mounted contralaterally on the robot. The six wheel-legs were mounted

in such a way to produce the nominal tripod gait of insect locomotion. The front and

back wheel-legs on one side of the robot were mounted in phase with each other and with the middle wheel-leg on the opposite side, and those three were mounted exactly out-of- phase with the other three wheel-legs, creating the alternating tripod pattern. Steering was accomplished by turning the front and rear wheel-legs in the desired direction while leaving the middle wheel-legs fixed. Instead of actively adapting the gait to the encountered terrain through sensors and controllers in feedback loops, torsion compliance in each of the axles allowed the robot to passively adapt its gait and acquire footholds on top of an obstacle with both its front wheel-legs in phase. The result was a robot that could travel at a speed of 3 body lengths per second, faster than any other known legged robot at the time.

In the research that followed Whegs™ I, a number of substantial improvements were

made on the design. Whegs™ II, shown in Figure 2.8, incorporated a servo-actuated body

flexion joint that allowed the robot to lift its front end to climb taller obstacles, much like

the rearing motion insects cause with their middle legs while climbing larger obstacles

(Allen, Quinn et al. 2003). The joint is then able to flex down to prevent high centering

once it has started to climb over the obstacle, which is the same function performed by

the cockroach body flexion joint. Whegs™ III was a sealed version of the Whegs™ concept,

13

incorporating rack-and-pinion steering as well as a body joint driven by a worm gear for

increased torque.

Figure 2.9: DAGSI Whegs™

DAGSI Whegs™ (Figure 2.9), the sixth robot in the Whegs™ line, implemented a novel body joint that is fully sealed and allows for pass-through of wiring and mechanical components (Boxerbaum, Oro et al. 2008). It uses a non-backdrivable worm gear body

joint that is both actively controlled and passively compliant. Steering is accomplished

through a servo-actuated Ackermann linkage which causes all six wheel-legs to move

through concentric arcs while turning.

Whegs™ II proved to be a reliable robot for testing purposes, and remains functional at the time of this writing. As such, it served as a test bed for a number of autonomous navigation systems. A two-antenna sensing system was developed and tested, demonstrating that the robot could use antennae to determine whether it should climb

14

over an shelf or tunnel under it, in the same way that cockroaches determine whether they should climb over or tunnel under an encountered shelf (Lewinger, Harley et al.

2005). A binaural sensing pod was also successfully used to perform obstacle detection and avoidance, using an ultrasound transmitter and two receivers to perform obstacle detection based on the interaural time difference, similar to the method used by bats and other animals (Lewinger 2006). This autonomy system was used in both fully autonomous and semi-autonomous modes. Whegs™ II also used a vision system to perform vision-driven goal seeking while avoiding obstacles using the binaural obstacle detection system.

The Whegs™ platform offers a number of advantages over other means of generating legged locomotion. Table 2.2 shows that the power-to-mass ratio of Whegs™ II is greater than both Robot II, a highly articulated hexapod robot, and RHex, another reduced- actuation robot. Because of the simplicity of the Whegs™ powertrain and actuation, it can be controlled using only three degrees of freedom while achieving a much more complex and effective legged locomotion pattern than a wheeled robot.

CWRU Robot II RHex Whegs™ II Number of motors 18 6 1+ Individual motor power (W) 6 20 90 Total motor power (W) 108 120 90 Gear-motor mass (kg) 2.7 1.8 0.87 Power / mass (W/kg) 40 67 103

Table 2.2: Power-to-mass analysis of selected robots

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2.3 Lessons learned from Whegs™ II

Because the service life of Whegs™ II was relatively long (2003 – 2008), a number of components needed to be repaired or replaced, providing an opportunity to learn what the weak points in the previous Whegs™ designs had been. The original robot had aluminum axles and plastic universal joints in the steering linkages, both of which were converted to steel for durability reasons. After extended use, the roller chains used to drive the axles stretched and slackened, causing the chain to pop off the drive sprockets.

The torsion devices were made of aluminum, and the torque was transmitted from the torsion device to the hex drive shaft only through a hex-broached hole in the end of the torsion device. This aluminum joint had stripped partially after repeated loading. In addition, the elastic element chosen for the torsion devices was a dental elastic band that, while easily replaceable, did snap frequently and would degrade under exposure to ultraviolet light. These elastic bands were replaced with o-rings, which have a much greater lifetime.

16

Figure 2.10: Whegs™ II tie rod steering arrangement

Whegs™ II employed a tie rod steering arrangement (Figure 2.10) which limited the total steering range somewhat relative to the capabilities of rack-and-pinion steering, and it eventually developed backlash and a considerable amount of friction. The body joint, while novel at the robot’s initial construction, also developed a considerable amount of backlash, and the body joint bearing itself developed a radial misalignment. Because the side rails were not tightly captured to one another, the joint would come close to sliding off its bearings and becoming unsupported.

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3 Design and Fabrication of Lunar Whegs™

The design of Lunar Whegs™ is the result of two main influences: on the one hand, the incorporation of the “lessons learned” during the construction, testing, and observation of wear and failure points of the preceding Whegs™ robots, and on the other hand the new challenges presented by the problem of creating a Whegs™-based lunar rover (Dunker, Lewinger et al. 2007; Dunker, Lewinger et al. 2008; Dunker, Lewinger et al. 2008). Certain key components of previous Whegs™ robots were included and improved, including the torsion devices, body joint, steering, drivetrain, and obstacle avoidance systems. At the same time, the challenges posed by the lunar design problem necessitated modifications to the body joint, steering, and body casing to seal the entire robot, as well as new feet for the robot and more attention paid to the routing of the robot’s wiring.

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Drive train Body flexion joint system Steering system Torsion compliance system

Figure 3.1: Schematic of Lunar Whegs™ showing main robot systems

3.1 Chassis

The Lunar Whegs™ chassis is designed for strength, modularity, and

interchangeability. In general, all plates are made of type 6061 aluminum, with 0.125”

thick horizontal plates and 0.25” thick vertical plates. Components are held together with

#4-40 anodized steel hex flat head cap screws, which are countersunk to avoid protrusions and allow for the attachment of the carbon fiber body panels. Both the front and the back 19

sections of the robot are made of two segments bolted together, which allows for easier

access and quicker assembly of the robot.

Lunar Whegs™ is sealed using 0.055” thick carbon fiber panels attached using #2-56

screws. Four panels enclose the front steering section along with two vertical Delrin®

plates, leaving the rest of the front section open for payload. The rear section of the robot

is enclosed using five carbon fiber panels, another Delrin® plate, and a clear polycarbonate

lid which allows viewing of the rear compartment and serves as a mounting point for

electronics and a wiring pass-through. The electronics enclosure is sealed against the lid

with a rubber gasket. All holes are plugged using a silicone sealant.

3.2 Torsion devices

The compliance afforded by the torsion devices is what allows Whegs™ robots to

adapt passively to terrain variations. These devices are elastic elements in series between

the drive motor and the wheel legs, and as such have always included three main

components: an inboard housing, an outboard housing, and an elastic element connecting the two. Previous Whegs™ robots, with the exception of DAGSI Whegs™, have had the luxury that the torsion devices could be relatively open to the surrounding environment. Lunar Whegs™, however, needed to have fully sealed torsion devices, and as a result the final design was a miniaturization of the torsion devices used on DAGSI

Whegs™.

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1 2

3 4 5

(1) Sprocket 6 (2) Case (3) Bowtie 7 (4) Ring (5) Torsion Spring (6) End Cap (7) Plastic Bearing

Figure 3.2: Torsion device for Lunar Whegs™ shown in exploded (left) and assembled (right) views.

Figure 3.2 shows an exploded view of one of the Lunar Whegs™ torsion devices. A

steel drive sprocket (hex broached) is attached to the drive side of the torsion device case

with screws. Inside the case, a bowtie-shaped steel part (also hex-broached) is supported

by a plastic bearing and limited in motion by two stops built into the case. The torsion spring is captured between the bowtie and the end cap. In order to apply an appropriate preload to the spring, the end cap and case interlock in a six-pointed castle pattern, with six holes in the cap which line up with the two holes in the case, allowing 60° resolution while applying the preload. A C-shaped ring allows screws to pass through the two appropriate holes while blocking the four unused holes. Finally, a hex-broached plastic bearing allows the output hex shaft to spin while preventing sand from entering the torsion device case.

21

Six torsion devices were manufactured and assembled, with three each of right- handed and left-handed springs, bowties, and end caps. The torsion devices were filled with marine grease before installation on the robot to provide lubrication and help reduce wear on the metal components inside.

3.3 Body joint

3.3.1 Initial design

Whegs™ robots have successfully used actuated body joints to climb over obstacles in a similar manner to cockroaches. Because Lunar Whegs™ would be operating in extreme conditions and would be carrying a payload, it was determined that the body joint ought to have a greater range of motion as well as a greater lifting capacity than previous

Whegs™ robots.

Whegs™ robots from Whegs™ II onwards have not had body joints capable of lifting the body joint while at rest, with the exception of Whegs™ III. Whegs™ III used a worm gear to drive the body joint, but it failed quickly because it did not have any passive compliance built into the body joint, with the result that the teeth on the body joint gear sheared under a shock load. The other Whegs™ robots could actuate the body joint up while driving on level terrain by using the inertia of the front section as it moved up and down. The non-backdrivability of the servo or motor attached to the body joint could fix the joint in place while the shaking of the body induced by the wheel-legs’ intermittent contact would move the front section up. The body joint could also be assisted during 22

obstacle climbing by the upwards reaction force on the front wheel-leg in contact with the

obstacle. As a result, the body joint could be actuated, but only while the drive motor was

also running.

Previous Whegs™ robots (Whegs™ III and DAGSI Whegs™) used brushless motors to

drive the body joint with a worm gear, but space considerations in Lunar Whegs™

suggested that two Hitec HSR-5995TG titanium-gear servos (torque rating of 2.35 N m)

were the best option to drive the body joint. On the basis of this stall torque rating, it was

initially believed that the two servos driving the body joint with a 2:1 gear reduction (9.40

N m) would be sufficient to drive the joint, allowing for ±45° of travel. While this would

not turn out to be the case, the mechanics of the joint were designed for that range of

motion, which would be maintained with the new body joint mechanism described below.

Figure 3.3 shows an early design for the body joint, in which the joint would be actuated by two servos attached to steel roller chains. The joint is covered by a compliant material on the top and bottom. This seal design was ultimately rejected because such a seal would not be able to keep out sand effectively due to the scissoring effect of the two halves against each other around the central axle.

Figure 3.4 shows images of the body joint as built. The compliant seal has been replaced by twin interlocking bearings made of hardcoat (Type III) anodized aluminum

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for improved wear resistance. A carbon fiber body panel seals off the front end of the rear

section, and hex-broached bushings prevent sand from entering around the drive shaft.

Figure 3.3: Initial design of body flexion joint, showing sprocket mounting (left) and compliant seal (right)

Figure 3.4: Final design of body flexion joint

In order to maintain the success that Whegs™ robots have had climbing over

obstacles in terrestrial environments, Lunar Whegs™ needed to have a functional body joint, but it also needed to be fully sealed, which required the design of a new type of body joint bearing.

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1

4

2 3

Figure 3.5: Body joint: Exploded view (left) and assembled view (right). The joint shown is for the right side of the robot; the bearing on the left side is a mirror image.

Figure 3.5 shows an exploded view of the sealed body joint design. The majority of the loading experienced by the body joint is carried by the interface between the two side rails (1) and (2). The radial loads on the bearing are transmitted through the steel drive shaft and the drive shaft bearings in each piece. Axial loads are transmitted by the face-to- face contact between the two side rails. The face of both rails is covered with a thin film of

Teflon® plastic which is specially etched on one side to allow epoxy to bond to it. As a result, all major loads on the body joint are carried by steel components or by aluminum components with a large contact surface.

The fact that the majority of the forces are already carried allows the seal components to be made of relatively thin (0.125” thick) anodized aluminum. The two anodized components (3) and (4) interlock by means of a cylindrical lip and groove, which are lubricated to reduce wear. The front body joint sprocket is then bolted to the outboard

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bearing piece (3) which is attached to the front segment of the robot, and the roller chain

is routed to the sprocket attached to the body joint servo output (not shown).

The magnitude of the backdriving torques on the body joint can be substantial

during the operation of the robot and are not limited to the available body joint torque.

The added climbing capability of the body joint can have mixed results for the overall

performance, because if a robot climbs up the front side of an obstacle it will frequently

fall down the back side. Since the impact load from this kind of fall was sufficient to

destroy the worm gear body joint in Whegs™ III, that failure mode inspired the

implementation of the passively compliant body joint used on DAGSI Whegs™. While

Lunar Whegs™ does not use a worm gear drive for the body joint, the fact that the servo output is geared down 3.6:1 means that the backdriving torque on the servos can also be quite high. In anticipation of this kind of loading, a compliant spider coupling was installed in series with the servo output as shown in Figure 3.6.

Figure 3.6: Spider coupling in series with body joint servo output

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The miniature spider is made of Hytrel and is rated for 4.75 N m, which is approximately twice the output torque of the body joint servos. Both ends of the coupling were custom-made; one end bolts directly to the servo horn while the other has a rectangular hole to receive the small sprocket.

3.3.2 Torque requirement testing

The initial design of the body joint was based on a 2:1 chain-and-sprocket transmission from each of two Hitec HSR-5995TG servos to the body joint. The servo output sprocket was press-fit into a cylindrical adapter which bolted to the aluminum servo horn. The sprocket, however, was not supported on the outboard side, with the result that the servo output spline was responsible not only for transmitting the required torque to the body joint but also for reacting the force and moment applied on the sprocket by the servo.

Figure 3.7: The initial method of torque transmission to the body joint, showing cantilevered servo output sprocket

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In initial bench testing, the body joint was in fact capable of lifting the front of the assembled robot. After only a few weeks of testing, however, the body joint seemed to be laboring more and more to raise the front of the robot, and ultimately the performance had degraded to the point where a successful raising of the body joint was only possible once a day, and only with substantial servo heating, suggesting that the servo performance degraded significantly when overheated. Because the body joint had functioned initially, it was believed that the cause of failure was likely the result of damage to the servos themselves or to the mechanical linkage between the servo and the body joint.

A series of tests was conducted to determine the actual stall torque of the servos

under three conditions: 6.0 Vdc, 7.4Vdc, and then 7.4Vdc again after having been stalled

for 15 s. Test procedures and results are reported in Appendix A. The testing indicated

two things: the servos may have been damaged, and servo overheating can limit the

repeatability of the servo output torque. In order to compare the numbers to the

estimated load, a SolidWorks model of the robot was populated with the mass densities of

each component’s material, so that the mass analysis function of the software could then

be used to obtain an estimate of the mass, centroid location, and inertia matrix of the

front section of the robot. Once this data was obtained, the static torque requirement for the body joint was found to be 5.8 N m. The analysis, however, revealed that the moment

of inertia of the front section is fairly large. It was also realized that a purely static analysis

28 would likely underestimate the required torque to lift the body joint because the motor must accelerate the front half of the robot as well as overcome gravity.

In the interim between the purchase of the body joint servos and the completion of the body joint servo testing, Hitec discontinued the HSR-5995TG model and introduced the HSR-5990TG servo as a replacement. It is likely that Hitec noticed the problems caused by overheating, because the new servo design uses a heatsink case and also contains a thermal breaker which shuts off the servo if it overheats. Benchtop testing indicated that the shutoff point corresponds to approximately 5 s of stalling. The torque rating of the servo is identical (2.3 N m at 6.0vdc, and 2.9 N m at 7.4vdc). The listed operating range of the servos is ±90°; the signal required to move the full range, however, could not be generated by the transmitter used for Lunar Whegs™, and it limited the range to ±45°.

The new HSR-5990TG servos were used as replacement servos for the body joint.

Although the thermal breakers, located within the servo housing, would prevent them from being damaged during high loading situations, the result would be a sudden loss of control in demanding circumstances, which led to the decision to gear down the servos and increase the torque. The smallest available pinion sprocket for this pitch was a 9- tooth sprocket; space constraints on the large sprocket limited it to 34 teeth, with a resulting transmission ratio of 34:9 or approximately 3.8:1. Table 3.1 shows the corresponding ranges and torques for different transmission options.

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Sprocket Transmission Ratio 2:1 3:1 34:9 (~3.8:1) 4:1 Body Joint Range ±45° ±30° ±23.8° ±22.5° Rated Body Joint Torque (N m) 9.3 14.0 16.7 18.6

Table 3.1: Sprocket ratios, joint ranges, torques for varying configurations of the body joint transmission. These values assume a servo with an initial range of ±90°.

Because the range of the new servos was electronically limited, the new body joint had a total range of ±11.9°, far less than the ±45° available range between the mechanical stops in the body joint. In addition to greatly curtailing the freedom of the robot, the range of motion was so small that one of the body joint chains fractured when the body joint experienced a strong backdriving torque. In order to take advantage of the full body joint range, the servos were opened and the physical stops and internal potentiometers were removed.

Potentiometer

Servo

2”

Output Coupling coupling gears

Figure 3.8: Position feedback for the body joint servo is accomplished using a potentiometer geared to the servo output.

To provide the servo with the necessary position feedback, the servo output was geared to a potentiometer mounted in the body joint as shown above in Figure 3.8. The

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gear ratio for the new fine-pitch gears is 1:1, the ratio of the servo’s internal feedback

ratio, and the potentiometer is a five-turn Bourns model which was mounted to the

vertical rail shown. After these modifications, the body joint can travel the desired ±45°

while providing 16.7 N m of torque.

The servo output shaft in the redesigned body joint is not supported by the servo

output horn. Instead, the shaft is held by two sealed bearings press-fit into the side rail

and an inboard vertical support, which carry all of the radial loading caused by the

tension in the body joint chain. The servo is held in place by the vertical rails but is free to

slide up and down a maximum of 2 mm in order to relieve any misalignments and allow

the bearings to take the full radial load on the sprocket.

Potentiometer Servo Coupling gears

Output coupling

Figure 3.9: Body joint view showing the servo shaft bearings and the method of servo capture

Because of changes to the pitch diameters of both sprockets, a tensioning sprocket was added to the body joint to take up most of the slack in the body joint chain. A small

31 amount of play was left to account for the flexing of the body joint during normal walking on flat surfaces.

3.4 Steering

Previous Whegs™ robots have used a variety of steering mechanisms to turn the robot. Whegs™ I and II both used rigid pushrods connected to the servo horn and to the steering knuckles using spherical couplings, with the effect that the steering rods would skew from one side to the other during the turn. This mechanism was useful because both robots had open frames with enough room to accommodate the front-to-back motion of the steering rods. DAGSI Whegs™ had the available space to implement a four-bar linkage that achieves full Ackermann steering, where all six wheel-legs travel on concentric arc paths during a turn. While Ackermann steering is certainly desirable, it is not imperative for robots with intermittent ground contact which can slip radially to some extent during a turn. The steering mechanism for Lunar Whegs™, therefore, is a mechanism like the one implemented on Whegs™ III: a rack-and-pinion mechanism with tie rods. Because the gear rack moves only in the lateral direction, the steering rods can be sealed at the point where they pass through the body. Figure 3.10 shows the Lunar Whegs™ steering mechanism and the steering rod pass-through.

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Figure 3.10: Steering for Lunar Whegs™: rack-and-pinion mechanism (left) and body pass-through (right)

3.5 Drive train

At the time that design for Lunar Whegs™ began, Whegs™ II was the robot in the

Whegs™ line that had been in use for the longest time and had also been subjected to the most severe testing. As a result, it was used as a baseline for long-term failure modes of

Whegs™ robots. In the case of the drive train, the most enduring problem appeared to be the backlash and eventual misalignment of the wheel-legs.

Whegs™ II used a chain-and-sprocket drive system attached to what was initially a set of 0.25” aluminum hex drive shafts, later converted to steel after the aluminum shafts broke. All of the chains and sprockets were 0.1475” pitch, with the exception of the chain between the drive motor and the first drive shaft, which was 0.25” pitch. The hex shafts were turned down to a constant diameter where they were affixed to the universal joints and to the wheel-legs. The aluminum cases of the torsion devices were broached to accept the hex shafts. Over time, the steel-on-aluminum joint wore and eventually stripped, with

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the result that there was nearly 50° of backlash from one end of the drive train to the other, which is close to the 60° offset necessary to produce out-of-phase tripod gait locomotion. Additionally, wear and slipping of set screws anchoring the drive components to the shafts meant that two of the wheel-legs were in phase with each other.

In order to avoid this problem, Lunar Whegs™ uses only steel-on-steel hex-broached joints for all torque transmission between the drive motor and the wheel-leg hubs, with no set screws other than one used in conjunction with the keyed output shaft of the drive motor. The higher motor output torque for Lunar Whegs™ necessitated the upgrade to

5/16” steel hex shafts and 0.25” pitch sprockets and chains. Each sprocket, then, is broached for the hex shafts and bolted to the inboard end of each torsion device. The bowties in the torsion devices and the wheel-leg hubs are also hex-broached, and the universal joints in the steering mechanisms were disassembled, broached, and then reassembled to accept the drive shafts. Because careful angular alignment during the broaching operation provides accurate results, the wheel-legs could be aligned properly in-phase and out-of-phase for the standard Whegs™ tripod gait.

The drive shafts are supported by a total of 25 double-sealed bearings containing hex bushings. The bearings are press-fit into the vertical supports, and the bushings are held inside the bearings using epoxy. After reassembly, the universal joints were greased and covered with specially sized rubber boots to protect them from grit and keep the lubricant inside the joint.

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3.6 Foot design

Foot design on Whegs™ robots has been an area of ongoing development since their inception. Feet are a critical component and are also easier to remove, change, and replace than many of the other components on the robot. Previous wheel-legs on full-size

Whegs™ robots have focused on a method to incorporate compliance into a rigid leg to mitigate some of the shock loading, whether by using bent and tempered spring steel or by attaching rubber to a rigid leg as on the current Whegs™ II feet. In these cases, rubber attachments also served to generate more traction for walking on surfaces such as tile, carpet, asphalt, or grass.

Lunar Whegs™ calls for a new type of leg and foot. A robot operating on loose substrate such as sand, soil, or fine regolith will already be dissipating most of the shock loading during normal walking; the primary concern is generating enough traction to propel the robot forward. In order to do this, the robot needs to stay on top of the sand, which requires maintaining a large surface area in contact with the sand the entire time that the foot is in contact with the ground.

Figure 3.11 shows two wheel-leg prototypes for Lunar Whegs™. The design on the left has one spring-tensioned ankle on each leg, which allows the foot to make a flat contact with the surface of the sand and rotate to stay parallel to the surface through the entire stance period. At the end of the stance period, the spring returns the foot to its initial position. The design on the right has no articulation but has a number of stacked layers

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which can be reconfigured for testing purposes. Both feet have a cupped base (inspired by camel feet) intended to compress the sand beneath the foot and gain more traction.

Figure 3.11: Two wheel-leg prototypes for Lunar Whegs™: articulated ankle (left) and rigid (right)

Initially, the legs with the spring-return ankle were fabricated and tested in the

SLOPE (Simulated Lunar OPErations) facility at NASA Glenn Research Center in

Cleveland, Ohio. Images of the Whegs™ II feet and the prototypes are shown below in

Figure 3.12. The old feet, shown on the top, clearly have problems staying on top of the

sand because their heel-claw, designed to hook onto rigid obstacles, merely digs into the

sand at the beginning of each step. The articulated leg, on the other hand, is able to stay

on the top of the sand for the duration of the step. What is not clear from these images,

however, is that the articulated foot is not able to generate enough traction because it has

a relatively flat sole, even with the cupped underside.

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Figure 3.12: Comparison of sand performance between Whegs™ II feet and prototype feet with articulated ankle

While the articulated foot could likely gain more traction with more development, it was ultimately not pursued because the joint introduced a failure point for a robot operating in a highly abrasive environment. Instead, the second rigid-ankle design was fabricated, with the modification that many of the layers would be made of Delrin® instead of aluminum in order to reduce the overall weight. Figure 3.13 shows the fabricated wheel-leg; performance results are discussed below in Section 5.3.

Figure 3.13: Fabricated rigid wheel-leg

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3.7 Modeling and fabrication

Lunar Whegs™ was modeled using SolidWorks 2006 (Education Edition). After the model was complete and checked for fit and consistency, solid body data was imported into MasterCam 8 for programming the mill operations. CNC milling was done on the

HURCO CNC mill in the Biorobotics Lab, and all other manufacturing operations were performed with the facilities in the machine shops on floors 2 and 8 of Glennan building

(Case Western Reserve University). Components for the body joint bearing were machined and subsequently hardcoat (Type III) anodized at Anodizing Specialists, Inc.

(Mentor, OH). Most plastic and metal stock and all fasteners were purchased from

McMaster-Carr Supply Company, while some gear and chain-drive products were purchased from W. M. Berg Corporation and Stock Drive Products/Sterling Instrument.

Assorted electronics were purchased from Tower Hobbies, Acroname, and other robotics suppliers. A complete bill of materials is listed in Appendix D.

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4 Mission Tasks

4.1 Robotic excavation teams

Lunar Whegs™ would be implemented in an ISRU capacity in a lunar mission as part

of a robotic excavation team. It has been proposed that Lunar Whegs™ could operate in

teams with two Lunar Whegs™ robots and one large dredger/hauler robot modeled after

NASA’s Cratos Rover, as shown in Figure 4.1 (Lewinger 2007).

The lunar regolith contains 40% oxygen, 0.9% water, and 0.5% hydrogen, according

to NASA sources. As a result, the required regolith collection per year for one person’s

water use is 120 m3, and the requirement for oxygen is 150 m3. Because the 14-Earth-day lunar night is too cold for either human-driven or robotic sorties, the collection during each lunar day needs to provide resources for twice the amount needed for one day.

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Figure 4.1: Proposed configuration for autonomous robotic excavation teams

Life Requirements on Earth and in Space

Item On Earth In Space kg gallons kg gallons per person per person per person per person per day per day per day per day Oxygen 0.84 0.84 Drinking Water 10 2.64 1.62 0.43 Dried Food 1.77 1.77 Water for Food 4 1.06 0.80 0.21

Table 4.1: Requirements for basic life-sustaining resources for one person (Tchobanoglous and Schroeder 1987)

In order to determine whether such a team would be a good choice for excavation, it can be compared with the alternative solution of sending an excavation attachment to the

Moon, which could be attached to the front end of the crew’s human-carrying rover.

Table 4.2 shows estimated performance data for the two options. Notable is that while the robotic team takes twice as much time to collect 2 m3 of regolith (the daily required

40 amount), its mass is 30-50% of the loader assembly’s mass and consumes 10% as much power.

Human Rover Robot Excavation with Loader Team 200-300 kg 100 kg Mass (loader assembly only) (per team) Power Consumption 4000-6000 W 250-400 W Payload 0.25 m3 0.25 m3 Estimated time per sortie 30 min 60 min Time to collect 2 m3 4 h 8 h

Table 4.2: Performance comparison between a loader attachment for a human rover and an autonomous robotic excavation team.

4.2 Autonomy

In order to function autonomously, Lunar Whegs™ needed to be able to detect and avoid obstacles. Previous obstacle detection in Whegs™ robots has involved the use of antennae to detect climbable obstacles and ultrasonic sensors to detect obstacles at a distance, as well as a mixed sonar-and-vision system which performed both obstacle detection and goal seeking. However, the lack of a lunar atmosphere eliminates sonar as a sensing mechanism, and antennae are only capable of short-range sensing. Instead, Lunar

Whegs™ uses the newly released Hokuyo URG laser rangefinder (mini LIDAR) shown in

Figure 4.2 to detect obstacles.

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3”

Figure 4.2: Hokuyo URG mini-LIDAR unit mounted to the front of Lunar Whegs™

The mini LIDAR unit has a range of 4 m and a maximum angular range of 240° with a vertical depth of 18 mm. In order to be able to process the data in real time, the range was limited to 90° and subdivided into eleven sectors, which allows for a scanning frequency of 10 Hz. The algorithm, developed by William Lewinger, determines the shortest distance reading within each sector and assigns that reading to the entire sector.

The sector with the farthest sensed distance, or the middle of a group of sectors at the same farthest distance, is selected as the desired heading unless that direction is determined to be a corner. A corner is detected if the sectors on either side of the desired heading are read as being nearer to the robot by a specified minimum threshold. If a desired heading is determined to be a corner, the robot steers hard in the opposite direction from the corner.

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Figure 4.3: Screen capture of obstacle avoidance algorithm. The blue arcs represent sensed distance, the red line and green line (hidden by blue) show the angular limits of the sensor, and the magenta line shows the selected heading.

4.3 Electronics and wiring

Power is supplied to the robot by means of two drive batteries (each 7.2vdc, 3600 mAh) connected in series to provide 14.4vdc and two servo and logic batteries (each

6.0vdc, 2000 mAh). In manual mode, the robot is controlled using a standard PCM hobby radio control transceiver; in autonomous mode one BrainStem microcontroller

(Acroname, Inc., Boulder, Colorado), a PIC-based microcontroller, processes the input from the mini LIDAR and controls the robot’s three degrees of freedom. A second

BrainStem microcontroller is present to enable the future expansion of vision-based goal seeking.

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All of the electronic wiring is routed to a box located on top of the rear segment of

the robot. Mounted to the box are the two switches and fuses for robot power, three

terminal blocks, and the BrainStem microcontrollers. The bottom of the box has a pass-

through hole which is aligned with another hole in the top body panel of the robot’s rear

section and sealed using a rubber gasket. The antenna for remote control is routed

through the lid of the box inside a piece of plastic tubing for protection. Each wire pass- through is sealed by means of a rubber grommet and silicone sealant.

Figure 4.4: Inside of electronics box

All wiring work was done by William Lewinger.

4.4 Actuated regolith scoop

In order to collect and transport regolith, the robot needs to have a scoop which can

pick up material, haul it without spilling, and dump it in a controlled manner at the

desired location. In addition, it needs to be stowed in the robot in such a way that it does

not interfere with regular operation.

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To solve this problem, a scoop was designed that would satisfy these requirements.

Because the mission requires three basic configurations, it was decided that the scoop should be actuated by one four-bar linkage driven by two servo motors, since four-bar linkages can be fully specified by three desired positions along the linkage’s path of travel.

The full motion can be generated by a mechanism with only one degree of freedom, and as a result the actuation can be provided by one or two servos mounted at one of the

linkage joints.

11 (1) Servo (2) Servo-to-spider adapter (3) Compliant spider (4) Spider-to-spring adapter (5) Torsion spring (6) Gearbox input shaft (7) Gearbox cap (8) Gears (9) Gearbox housing (10) Linkage arms (11) Side rail

9 10 6 8 5 7 3 4 2 1

Figure 4.5: Exploded view of scoop assembly, showing spider coupling, torsion spring, and gearbox

The resulting design, shown in Figure 4.6, uses two servos to drive the scoop linkage.

Each servo is attached to a spider coupling and a pre-tensioned torsion spring to isolate

the servos from shocks encountered while the scoop is moving along the ground. The

output of the torsion device is geared to the scoop linkage through a 2:5 spur gear

45 transmission inside a sealed gearbox. The result of this gearing is that the transmission output provides 1.9 N m of torque through an operating range of 225°.

Figure 4.6: Actuated scoop, showing extreme positions in range of motion: stored (left) and scooping (right)

The body of the scoop is constructed from an aluminum frame 0.125” thick and is covered with a carbon fiber skin, providing a smooth floor for the inside of the scoop.

The front edge of the scoop is covered by a replaceable steel blade and wear strip screwed to the underside of the scoop body, with a small 90° lip on the inside of the front edge to help keep the material inside the scoop while moving.

Figure 4.7: Different dumping options for Lunar Whegs™: flat terrain (left) and a specially designed step (right). Scoop is shown in red.

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Due to space constraints on the placement of links, as well as the fact that the mechanism only has one degree of freedom, the scoop linkage is not able to achieve an angle steep enough to dump on its own. The robot, however, can actuate its body joint down to dump material from its scoop. Depending on the configuration of the location where it needs to dump the material, it can effect different dump angles. If the robot is dumping onto a location on flat ground, it can generate a dump angle of 32°, while it can generate a dump angle of 54° if the dump location supports the rear body segment alone

(allowing the robot body to pivot down the full 45° range).

Design work on the actuated scoop was done by Alex Hunt.

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5 Robot Performance

5.1 Performance specifications

Whegs™ II Lunar Whegs™ Dimensions (cm) overall chassis overall chassis Length 60 47 62 48 Width 39 35 50 32 Height 19 6 19 7 Mass (kg) Chassis only 5.6 9.8 With batteries 6.5 11.0 Speed (body lengths per second) 2.30 1.91 Drive motor output torque (N m) 22.7 64.6 Turning radius (body lengths) At minimum speed 1.17 1.26 At full speed 1.62 0.95 Body Joint Payload (kg) Dead lift -1.2 1.4 Holding capacity 1.5 3.7

Table 5.1: Comparison of performance of Whegs™ II and Lunar Whegs™

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Table 5.1 shows the basic performance specifications for Whegs™ II and Lunar

Whegs™. Speed and turning data are shown for rubber tread, rigid wheel-legs operating

on a tiled floor.

5.2 Autonomy

Having been outfitted for autonomous obstacle avoidance, Lunar Whegs™ was tested

walking in a slightly cluttered hallway and turning a corner. Out of three attempted left- hand turns and three attempted right-hand turns, the robot successfully executed all six turns and started down the next hallway without hitting either wall. During these tests,

Lunar Whegs™ operated with full autonomy and no operator control.

5.3 Mars Yard testing

Lunar Whegs™ was tested at the Canadian Space Agency (CSA) Mars Yard during the

2008 Planetary and Terrestrial Mining Sciences Symposium (Lewinger, Dunker et al.

2008). Under operator control, Lunar Whegs™ demonstrated its ability to travel over flat sandy areas as well as climbing up and down inclines as steep as 30° and over rocks as tall as 6 in. It also successfully crossed a number of regions with a mixed rock-sand surface, and was able to use its steering and body joint capabilities to free itself when stuck.

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Figure 5.1: Images of Lunar Whegs™ at the Mars yard at the Canadian Space Agency (PTMSS 2008 conference) in Montreal

While previous research on the usefulness of body joints on Whegs™ robots has focused on discrete obstacle climbing, video footage of Lunar Whegs™ in sand

demonstrates another function of a Whegs™ body joint. Actuation of the body joint on a

loose substrate affects the weight distribution on the three axles, which allows the robot to shift support to a more stable foothold and gain traction.

5.4 Sandbox testing

Lunar Whegs™ was tested in a sandbox constructed in the Center for Biologically

Inspired Robotics to determine traction, speed, and turning capabilities in sand. The

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sandbox itself is filled with play sand of relatively fine grade, filled approximately 4” deep,

which is deep enough to prevent the wheel-legs from hitting the bottom of the sandbox as

long as they are not digging into the sand.

Figure 5.2: Lunar Whegs™ in testing sandbox

Quantity Value Speed 0.8 bl/s (0.40 m/s, 1.3 ft/s) Turning Radius (forward) 0.85 bl (41 cm, 16 in) Turning Radius (backward) > 2.2 bl (104 cm, 41 in) Pulling Load 60 N (13.4 lb)

Table 5.2: Performance in sandbox

Table 5.2 shows the handling and towing capabilities of Lunar Whegs™ as tested in

the sandbox. The turning radius is notably tight driving forward, which is not the case driving in reverse. The improved forward turning radius is likely due to the torsion devices on the robot, which are able to function as a differential. Observation of the video shows that the torsion devices on the inside of the turn are winding, whereas those on the

51 outside are not; the unidirectional nature of the torsion devices prevents this from occurring while driving backward. The 60 N (13.4 lb) towing capacity is greater than the predicted load on the scoop, which is anticipated to be no greater than 4 lb.

5.5 Obstacle climbing

Figure 5.3: Images showing successful climb of 5” obstacle

Figure 5.4: Images showing successful climb of 6” obstacle

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Figure 5.5: Unsuccessful climb of 7” obstacle

Lunar Whegs™ is able to climb a 6” step obstacle (with a solid front face) using its

hard feet designed for loose sand, which is its maximum climbing height for a step

obstacle. This is remarkable considering its feet have a very low coefficient of friction with

this obstacle. This obstacle, shown in Figure 5.4 above, is 1.58 times the wheel-leg length,

which is slightly lower than Whegs™ II’s climbable height of 1.7 times the leg length.

Whegs™ II Lunar Whegs™ Wheel-leg length 10 cm 9.5 cm Inter-axle distance 21.6 cm (8.5 in) 21.6 cm (8.5 in) Body joint range ±30° ±45°

Table 5.3: Comparison of some Whegs™ II and Lunar Whegs™ parameters relevant to obstacle climbing

Figure 5.5 above shows the reason this is the case: at a 7” obstacle, the underside of

the robot body hits the edge of the step and prevents the rear wheel-leg from acquiring a foothold on the top of the step. Part of the reason why this problem occurs is that the center of mass is in the rear of the robot. Because both the batteries and the drive motor

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are in the back half of the rear section, the center of gravity of the robot does not cross the obstacle until the third set of wheel-legs have. Essentially, the traction on the front feet is insufficient to pull up the back end of the robot because they do not bear enough of the load on the robot and they have a low coefficient of friction on this surface. This capability could possibly improve when the scoop in the front of the robot is heavily

loaded, since the farther forward the center of gravity is, the more traction the front and

middle wheel-legs will be able to acquire on top of the obstacle (Boxerbaum, Oro et al.

2008; Boxerbaum, Oro et al. 2008). However, testing with a weight of 2.2 lbs attached to

the front of the robot did not allow the robot to climb the obstacle, and it may take a large counterweight to change the weight distribution sufficiently.

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6 Conclusions and Future Work

6.1 Conclusions

Lunar Whegs™ demonstrates that a Whegs™ robot can function well under some of

the same environmental conditions as that on the Moon or Mars. Adapted feet allow for

more effective walking on sand while maintaining the characteristic climbing capacity of

Whegs™ robots for discrete obstacle climbing. The new body joint design has shown a

new way of driving a Whegs™ body joint with servo motors that provides both a wider

angle range and increased torque while keeping the joint sealed. This new body joint

allows for greater obstacle climbing capability as well as more effective dumping and

weight distribution while operating in sand. The sealed chassis prevents sand from interfering with the operation of the robot and protects the mechanical components

inside.

6.2 Future work

While Lunar Whegs™ has shown its ability to operate in sand, there is a large amount

of work involved in taking a robot from a terrestrial prototype to a flight-ready rover.

Additional work remains to be done to seal the robot against actual lunar regolith, which

is finer than play sand or the material used at the CSA Mars Yard. Any excess material on

55 the robot, especially on the metal chassis, should be removed to lighten the robot as much as possible, and a full thermodynamic analysis of heat losses is necessary to ensure that the robot is able to both remove excess heat and also keep the electronics warm enough to function.

While all of these are critical tasks for the design of a lunar rover, Lunar Whegs™ itself has the capacity to serve as a test bed for further Whegs™-related testing, in addition to more general experiments involving robot teamwork and autonomy applications.

Mechanically, the robot would benefit from the fabrication of an optimized set of sand feet with fewer separate components, and a wider enclosure section could be fabricated to protect the exterior drive chains from foreign material. With the wider body joint range and higher torque, it could be used to investigate climbing capabilities and control strategies for actuation of the body joint while climbing over obstacles or traversing irregular terrain. Electronically, it will likely incorporate a vision system in the near future which will be used to perform goal-seeking tasks while using autonomous obstacle avoidance. Additionally, it could be outfitted with any number of sensors, communications equipment, or computing hardware to perform specialized tasks in harsh environments with irregular terrain.

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Appendix A: Body Joint Servo Testing

Because the lifting capacity of the original body flexion joint had decreased over time, a series of tests was developed to determine the cause of the poor performance and the necessary solution. One of these tests involved characterizing the performance of the body joint servos at different voltages as well as after being stalled and overheated. This section details the test setup, procedure, and results for the servo testing.

A.1 Setup

Figure A.1: Setup for servo torque test

In order to perform the servo torque measurements, a servo was gently clamped to the tabletop using a C-clamp, with a fish scale (50 lb capacity) gently clamped to the table leg (shown in Figure A.1). A specially machined arm from Delrin weighing 0.56 N (2 oz) was attached to the servo. The arm had a hole 8.00” from the servo attachment, and this

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hole was where the hook from the scale was attached. The servo was connected to the

Lunar Whegs™ receiver unit, and the battery connections for the receiver were connected

to a voltage supply.

A.2 Procedure

1. Adjust the servo control to the midpoint of its range of motion. 2. Set the voltage supply to 6.0 V. 3. Power on the transmitter. 4. Power on the receiver and servo. 5. Turn the servo control until the scale chain is taut and the servo has stalled. 6. Record the force on the scale and the current draw. 7. Quickly relax the tension on the scale. 8. Repeat (1-7) at 7.4 V 9. Stall the servo for 15 s at 7.4 V, relax the chain, then stall the servo again. 10. Record the force on the scale and the current draw. 11. Repeat (1-10) for the rest of the servos.

A.3 Results

Under normal operating conditions, both servos performed between 65% and 80% of

the Hitec rated torque (2.3 N m at 6.0vdc, and 2.9 N m at 7.4vdc). After having been

overloaded and overheated, the performance drops to approximately 50% of the rated torque. Table A.2 shows the projected actual performance in the robot, with two servos working in parallel, geared down either 2:1 (initial gearing), 3:1, or 4:1.

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Force Radius Current Moment (N) (cm) (A) (N m) Servo 1 8.9 20.3 2.5 1.81 Weight of bar 0.6 10.2 0.06 Stall torque 2.5 1.86 Percent of Rating 79% 6.0V Servo 2 7.5 20.3 2.6 1.53 Weight of bar 0.6 10.2 0.06 Stall torque 2.6 224 Percent of Rating 67% Servo 1 10.0 20.3 2.8 2.03 Weight of bar 0.6 10.2 0.06 Stall torque 2.8 296 Percent of Rating 74% 7.4V Servo 2 10.0 20.3 3.2 2.03 Weight of bar 0.6 10.2 0.06 Total 3.2 296 Percent of Rating 74% Servo 1 6.4 20.3 3 1.30 Weight of bar 0.6 10.2 0.06 Total 3 192 7.4V, Percent of Rating 48% After Servo 2 6.4 20.3 2.6 1.30 Overload Weight of bar 0.6 10.2 0.06 Total 2.6 192 Percent of Rating 48%

Table A.1: Test results for servos at varying voltages and load

Torque (N m)

6.0 V 7.4 V 7.4 V, Overload 2 servos, 1:1 3.4 4.1 2.7 2 servos, 2:1 6.8 8.3 5.4 2 servos, 3:1 10.2 12.4 8.0 2 servos, 4:1 13.6 16.5 10.7 Current (A) 5.1 6.0 5.6

Table A.2: Available body joint torque for different transmission ratios, voltages, and load

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The static torque required to hold the body joint flat with the front end of the robot unsupported is 5.8 N m as calculated from mass analysis of the robot solid model (shown below in Section 0). Based on this information, the recommended course of action was to change the 18-tooth sprocket on the servo to a 9 tooth sprocket. If more torque is required, it would also be possible to change the servo voltage to 7.4vdc. Beyond that, the next option is to change the body joint drive from servos to a Maxon motor.

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Appendix B: Mechanical Drawings ISOMETRIC ISOMETRIC

FRONT RIGHT

TOP

All dimensions shown are in cm.

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Appendix C: Selected Design Calculations

C.1 Drive train

Motor calculation

Define working torque as maximum torque required W to walk on flat ground (standing up on one leg)

Safety factor = 1.5 r Robot weight = 20 lbf 60° r = 4.5

TWr= sin(60D ) T ==⋅=(20)(4.5)sin(60D ) 78 lb in 8.81 Nm nT ==(1.5)(8.81) 13.2 Nm

Selected motor: Maxon RE-35 90W, model 118776, stall torque 872 mNm

Selected transmission: Maxon GP 42 C, model 203123, 74:1 reduction, max torque 22.5 Nm

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Drive shaft calculation

16T Max shear stress for hexagonal cross-section: τ = max πd3

22.5 Nm=⋅ 199.1 lb in 16T 16(199.1) τ == =33.2 ksi d max πd33 π(0.3125") nτmax ==(33.2)(1.5) 49.9 ksi

12L14 steel: 60 ksi yield strength

Selected drive shaft: McMaster #6606K13 12L14 steel hexagonal bar, 5/16” Drive chain calculation

Selected sprocket: McMaster #6793K11, 0.25” pitch, pitch dia. 1.4397” 34 teeth

Axle spacing: 8.5”

(8.5)(2)+=π (1.4397) 21.52" nominal chain length = 86 pitches

Allowable load for chain: 140 lb working, 1050 lb breaking

Equivalent torque (working): (140 lb)(0.7199")=⋅= 100.8 lb in 11.39 Nm Working torque from motor: 8.81 Nm

Equivalent torque (breaking): (1050 lb)(0.7199")=⋅= 755.8 lb in 85.41 Nm Max drive torque from motor = 22.5 Nm

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C.2 Steering

Wheel base (distance between axles) = 8.5” Track = 15”

15”

1.8” 1.25” 12.53”

The steering linkage is a planar linkage having six links, with the gear rack constrained to slide left-to-right only.

Inside angle Outside angle (deg) (deg) 0.00 0.00 5.00 4.39 10.00 9.63 15.00 15.02 20.00 20.47 25.00 25.88

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C.3 Body joint

Figure C.1: Portion of Lunar Whegs™ front end used for calculating mass, with mass centroid and principal axes of inertia shown.

x O T W

x = 16.7 cm IImr=+222 =261.76 + (3.56)(16.7) = 1250 kg ⋅ cm 0 x m = 3.56 kg Wmg==34.9 N

∑MIα= TWxIα−= Tα=+(1250) (34.9)(16.7) =+ 1250 α 583 (Ncm) =+ 12.5 α 5.83 (Nm)

With an available body joint torque of 13.6 Nm, the front section of the robot can achieve an angular acceleration of 0.62 rad/s2

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Appendix D: Bill of Materials

Cost Qty Description Vendor Part Number (USD) Accessories 4 Battery Charger Tower Hobbies LXUF43 220 Batteries 2 Integy Intellect 3600 8.4V 7C Stick Pack Battery Tower Hobbies LXLFW5 75 2 Hobbico HydriMax 6.0V 2000mAh NiMH AA Battery Tower Hobbies LXNHS4 50 Body Joint 2 Roller chain, .1475 pitch, 8.85" long, stainless steel WM Berg RC14SS-60 100 2 Precision Potentiometers 7/8 WW 5KOHMS 0.25% 5TURNS Digi-Key 652-3545S-1-502 45 2 Self-Locking Cup Point Set Screw, 6-32 Thread, 1/4" Length McMaster-Carr 91385A144 <5 1 Teflon® sheets, .015" Thick, 12" X 12" McMaster-Carr 8711K72 10 4 Cone Point Set Screw, 2-56 Thread, 1/8" Length McMaster-Carr 92695A007 <5 4 Double Sealed Ball Bearing for 1/8" Shaft Dia. McMaster-Carr 6138K63 25 12 Brass Thick Flat Washer #8 Screw Size McMaster-Carr 95395A207 15 2 Hytrel Spider for Miniature Spider Coupling McMaster-Carr 2401K82 10 4 Stainless Steel Shim Washer, .030" Thick, 3/8" ID, 5/8" OD McMaster-Carr 97022A495 <5 2 Self-Locking Shoulder Screw, 1/8" Shoulder Dia, 3/8" Shoulder McMaster-Carr 93996A526 5 2 ROW-L-ER CHAIN LINK SRS <=3SS WM Berg 14EM10S-9 20 2 ROW-L-ER CHAIN LINK SRS <=3SS WM Berg 14SP3S-34 35 4 88-tooth 96 pitch gear, 0.25 in wide, .937 OD WM Berg P96S5-88 75 Drive Train 1 Planetary Gearhead GP 42 C, 74:1 Reduction Maxon Motor 203123 265 1 RE 35, Dia. 35 mm, Graphite Brushes, 90 watt Maxon Motor 118776 250 2 Floating Roller Chain Tensioner for #25 Chain McMaster-Carr 5973K1 60 4 Pin-and-Block Universal Joint, 5/16" Bore Dia McMaster-Carr 6443K46 110 1 Self-Locking Cup Point Set Screw, 8-32 Thread, 3/16" Length McMaster-Carr 91385A189 15 4 Dowel Pin, 3/32" Diameter, 5/8" Length McMaster-Carr 98380A440 <5 6 Torx Drive Socket Head Cap Screw 8-32 Thread, 3/8" Length McMaster-Carr 92610A192 <5 1 12L14 Carbon Steel Hexagonal Bar, 5/16" Hex Size, 6' Length McMaster-Carr 6606K13 10 7 Hexagon Hole Sleeve, 0.315 Across Flats SDP/SI A 7C20-05 65 6 Sleeve Bearing for 3/16" Shaft Dia, 1/4" OD, 1/4" L, 3/8" Flange OD McMaster-Carr 6362K201 50 25 Double Sealed Ball Bearing for 9/16" Shaft Dia, 1-3/8" OD McMaster-Carr 6384K75 215 2 Steel Roller Chain #25, 1/4" Pitch, 0.130" Dia, 2' McMaster-Carr 6261K2 15 12 Nylon Spacer, 3/16" OD, 3/16" Length, #4 Screw Size McMaster-Carr 94639A704 <5 6 Polyurethane Flat Disc Spring, .343" ID, .75" OD, .125" Thick McMaster-Carr 94045K142 5 4 Metric Flat Head Socket Cap Screw, M4 Size, 8mm Length McMaster-Carr 91294A188 <5 3 Torsion Spring 90 Deg Angle,.776" Coil OD,.095" Wire, Ccw/Rh McMaster-Carr 9287K109 20 3 Torsion Spring 90 Deg Angle,.776" Coil OD,.095" Wire, Cw/Lh McMaster-Carr 9287K153 20 2 Clamp-on Shaft Collar, 8 mm Bore, 18 mm OD, 9 mm W McMaster-Carr 6063K14 10 6 Sprocket for #25 Chain, 1/4" Pitch, 18 Teeth, 1/4" Bore McMaster-Carr 6793K11 25 6 Black-Oxide Flat Washer #8 Screw Size, 3/16" ID, 7/16" OD McMaster-Carr 98029A043 <5 1 Steel Roller Chain #25, 1/4" Pitch, .13" Dia, 1' L McMaster-Carr 6261K1 5 6 Nylon Bearing Flanged, for 5/16" Shaft Dia, 7/16" OD, 7/16" L McMaster-Carr 6389K232 5 6 Nylon Bearing Flanged, for 1/4" Shaft Dia, 3/8" OD, 3/8" L McMaster-Carr 6294K61 10 1 Bronze Flanged Bearing for 12 mm Shaft Dia, 18 mm OD, 8 mm L McMaster-Carr 6659K17 <5

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Electronics 1 Futaba 7CAP 7-Channel PCM/2 S3151 Servos 75MHz Tower Hobbies LXRLM8 230 1 Devantech HBridge Motor Driver Acroname R133-MD03 135 4 HSR-5990TG (417 oz. in.) Digital Standard Servo Lynxmotion S5990TG 500 2 BrainStem GP 2.0 Acroname S25-GP2-BRD 160 2 EMS Servo Reverser Futaba J Tower Hobbies LXAFN1 40 2 Metric Flat Head Socket Cap Screw, M3 Size, 8mm L, .50mm Pitch McMaster-Carr 91294A128 <5 1 Team Orion Universal Extension Cable 300mm Tower Hobbies LXNAD8 5 C10-SER-INT- 1 Serial Int Connector Extender Acroname CONN-EXT 5 1 Aluminum F Hex Standoff 1/4" Hex, 1-1/2" L, 4-40 Screw Size McMaster-Carr 91780A171 <5 1 Aluminum M-F Hex Standoff 1/4" Hex, 1" L, 4-40 Screw Size McMaster-Carr 93505A436 <5 Enclosure Robot WCC- 1 0.059 Twill-Weave Hexcel Texalium- Silver CF Sheet 11x16 Marketplace THT0591116s 90 Robot WCC- 1 0.059 Twill-Weave Hexcel Texalium- Silver CF Sheet 11x8 Marketplace THT0591108s 45 3 Polycarbonate Sheet 1/8" Thick, 12" X 12", Clear McMaster-Carr 8574K26 20 1 Adhesive-Back Neoprene Rubber 1/8" Thick, 6" X 6" McMaster-Carr 8463K421 5 6 Rubber Grommet 5/32" ID, 1/2" OD, for 3/8" Dia Panel Hole McMaster-Carr 9600K41 <5 Fasteners 16 Button Head Socket Cap Screw 8-32 Thread, 5/8" Length McMaster-Carr 91255A196 <5 8 Self-Lock Socket Head Cap Screw 4-40 Thread, 1/2" Length McMaster-Carr 91205A110 5 4 Self-Lock Socket Head Cap Screw 4-40 Thread, 1/4" Length McMaster-Carr 91205A105 <5 4 Black-Oxide Socket Head Cap Screw 4-40 Thread, 3/4" Length McMaster-Carr 91251A113 <5 74 Button Head Socket Cap Screw 8-32 Thread, 1/2" Length McMaster-Carr 91255A194 10 24 Black Oxide Flat Head Sckt Cap Screw 8-32 Thread, 3/8" Length McMaster-Carr 93791A472 5 128 Flat Head Socket Cap Screw 4-40 Thread, 1/2" Length, Black Oxide McMaster-Carr 91253A110 10 12 Flat Head Socket Cap Screw 4-40 Thread, 3/8" Length, Black Oxide McMaster-Carr 91253A108 <5 72 Nylon Spacer 1/4" OD, 3/4" Length, #4 Screw Size McMaster-Carr 94639A205 5 32 Flat Head Socket Cap Screw 4-40 Thread, 1/4" Length, Black Oxide McMaster-Carr 91253A106 5 76 Pan Head Phillips Machine Screw 4-40 Thread, 2" Length McMaster-Carr 91772A121 5 4 Hex Nylon-Insert Locknut, 4-40 Screw Size, 1/4" Width, 7/64" Height McMaster-Carr 90101A004 <5 12 Flat Head Socket Cap Screw 4-40 Thread, 3/4" Length McMaster-Carr 90585A206 5 12 Black-Oxide Pan Head Phil Machine Screw, 2-56 Thread, 1/8" Length McMaster-Carr 91249A042 <5 8 Black-Oxide Machine Screw Nut 4-40 Screw Size McMaster-Carr 96537A120 <5 7 Black-Oxide Pan Head Phil Machine Screw, 4-40 Thread, 3/8" Length McMaster-Carr 91249A108 <5 9 Flat Head Phillips Screw Black-Oxide, 4-40 Thread, 3/8" Length McMaster-Carr 96640A056 <5 96 Black-Oxide Pan Head Phil Machine Screw, 2-56 Thread, 1/4" L McMaster-Carr 91249A050 5 8 Black-Oxide Pan Head Phil Machine Screw, 2-56 Thread, 3/16" L McMaster-Carr 91249A046 <5 16 Machine Screw Nut 8-32 Screw Size, 11/32" Width, 1/8" Height McMaster-Carr 90480A009 <5 Steering 1 2 ft steel rack 32 pitch teeth 14.5degree SDP/SI A 1C12-N322 35 2 1.5 D brass spur gear 14.5degree 32 pitch SDP/SI A 1B 2-N32048 30 1 Alloy 360 Brass Rod with Certification 3/16" Diameter, 6' Length McMaster-Carr 2572T13 15 4 Dowel Pin, 1/8" Diameter, 1/2" Length McMaster-Carr 90145A471 <5 4 Bellow for Universal Joint, .65" ID X 1.32" L X 1.06" OD McMaster-Carr 94205K73 40 8 Self-Locking Button Head Cap Screw 4-40 Thread, 3/8" Length McMaster-Carr 92360A107 5 1 Steel Rod 3/16" Diameter, 6' Length McMaster-Carr 4416T11 5 1 Alloy 360 Brass Rectangle 1/4" Thick X 1" Wide X 6" Length McMaster-Carr 8954K337 5 1 Steel Rod 3/16" Diameter, 3' Length McMaster-Carr 9120K9 <5 4 Bronze Flanged Bearing for 3/16" Shaft Diameter, 5/16" OD, 1/2" L McMaster-Carr 6338K311 <5

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Stock 2 Alloy 6061 Aluminum Sheet, 1/8" Thick, 12" X 24" McMaster-Carr 89015K28 45 2 Black Delrin Sheet, 1/2" Thick, 12" X 12" McMaster-Carr 8575K117 85 1 Alloy 6061 Aluminum Sheet, 3/4" Thick, 8" X 8" McMaster-Carr 89155K62 40 1 Alloy 6061 Aluminum Bar, 1" Thick X 4" Width X 1' Length McMaster-Carr 8975K322 35 1 Alloy 6061 Aluminum Sheet .375" Thick, 12" X 12" McMaster-Carr 9246K23 35 1 4142 Stl Hardened Flat Stock, 1/4" Thick, 2-1/2" Width, 1-1/2' Length McMaster-Carr 8892K247 30 1 Alloy 6061 Aluminum Bar, 1/2" Thick, 6" Width, 1' Length McMaster-Carr 8975K442 25 6 Alloy 6061 Aluminum Sheet, 1/8" Thick, 12" X 12" McMaster-Carr 89015K18 155 2 Alloy 6061 Aluminum Sheet, 3/8" Thick, 8" X 8" McMaster-Carr 89155K32 50 1 Alloy 6061 Aluminum Bar, 1-1/2" Square, 1' Length McMaster-Carr 9008k461 20 7 Alloy 6061 Aluminum Sheet, 1/4" Thick, 12" X 12" McMaster-Carr 9246K13 150 1 4142 Stl Hardened Flat Stock, 3/8" Thick, 1" Width, 1-1/2' Length McMaster-Carr 8892K263 20 1 Black Delrin Rectangular Bar, 3/4" Thick, 2" Wide McMaster-Carr 8662K53 15 1 Alloy 6061 Aluminum Sheet, .063" Thick, 12" X 12" McMaster-Carr 89015K37 15 1 Alloy 6061 Aluminum Bar 3/8" Thick, 3" Width, 1' Length McMaster-Carr 8975K911 10 1 Alloy 6061 Aluminum Bar 5/8" Thick, 1-1/2" Width, 1' Length McMaster-Carr 8975K431 10 Total: $4005

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