Scarab Design Carnegie Mellon 13 -14 December 2007

Unique combination of drilling & driving on the moon Central issues Solutions Drilling loads Weigh enough Mount drill on center Lower drill to ground Lunar terrain Agile suspension Adjustable suspension Low cg CMU | 13 December 2007 2

Design approach Strong, slow & reliable Serial work machine Face disparate needs of drilling & driving Arrive at capabilities that complement each other CMU | 13 December 2007 3

Weighing enough Robot weight on lunar surface must support drilling operation • Up to 250 N downforce & 50 Nm torque required for drilling • Reserve 150 N passing through wheels for stability, torque & margin against uplift and spin Total weight on lunar surface > 400 N / 1. 622 m/s 2 250 kg vehicle mass CMU | 13 December 2007 4

Mounting drill • Fixed to chassis vs. articulated • Strength & stiffness of load path through chassis & suspension back to the ground • Dual as instrument mast CMU | 13 December 2007 5

Mobility design • 4 wheels, directly driven • Skid steered – Simplicity & Lunokhod precedence • Passive kinematic suspension • 1 mechanical release • Differential – Maintain rectangular stability pyramid base • Linkage differential – Suspension provided attach points – Frees drill workspace – Stiffness • Pose adjustment – Actuate height of each side – Outboard of differencing effect CMU | 13 December 2007 6

Suspension CG h = 0. 6 m 1. 4 m 1. 3 m Stability pyramid CMU | 13 December 2007 7

Wheel actuation • • • Local amplifier Brushless motor 5: 1 planetary 80: 1 harmonic drive 400: 1 total reduction Rim pull ~ vehicle weight CMU | 13 December 2007 8

Agile suspension • Passive matching of terrain • Large stroke for terrain approaching wheel diameter in size • Steady platform for sensing CMU | 13 December 2007 9

Agile suspension Twist course video CMU | 13 December 2007 10

Underbody shape Maintains 30 cm belly clearance with a wheel on 30 cm positive obstacles Keeps drill tip closest to ground when kneeling 30 cm CMU | 13 December 2007 30 cm 11

Lowering drill • Major benefit for drill system • Sensors inspect site prior to kneeling • Scarab poses with belly just above ground CMU | 13 December 2007 12

Pose adjustment mechanism • • Raises & lowers by actuating wing angle (independent L & R) Center link bisects wing angle: enables lift-and-level body averaging Retains advantages of passive rocker bogie Many ways to implement CMU | 13 December 2007 13

Mobility benefits • • • Climbing slopes otherwise unable to Leaning into cross-slopes for stability Autonomous body roll leveling Raising to avoid or recover from high centering Changing wheelbase in reaction to periodic terrain • Inch-worming out of dugin condition CMU | 13 December 2007 14

Scalability • Body is readily modifiable to suit payloads • Configuration is scalable in both directions CMU | 13 December 2007 15

Specifications Mass: 280 kg Weight: 460 N 2750 N Power (driving): Power (posing): Power (idle): 78 W Speed: 200 W (peak) 380 W (peak) 5. 0 cm/s (6. 0 cm/s max) Height (with drill tower): 2. 2 m high stance, 1. 6 m low stance Width (wheelbase): 1. 4 m Length (wheelbase): 0. 8 - 1. 3 m Aspect (track/wheelbase): 1: 1 low stance, 1: 2 nominal, 1: 7 high Wheel diameter: 60 cm CMU | 13 December 2007 16

Additional Material

Specifications CG height: 0. 64 m nominal, 0. 60 m low, 0. 72 m high Static pitchover: Static rollover: 42° nominal stance, 29° high, 45° low 53° nominal stance, 48° high, 55° low Maximum / minimum straddle: 57 cm, Belly contact Approach / departure angle: 105° nominal stance Breakover angle: 115° nominal stance Rim pull (single wheel): 2500 N Drawbar pull: 1560 N (medium-coarse grain sand) CMU | 13 December 2007 18

Design solution • Drill implementation – Central location on vehicle to maximize weight for downforce – Direct mounting to chassis – Fixed drill structure • Reduced actuation • Functions as navigation mast • Simplifies kinematics & mass properties • Adjustable kinematic suspension – Body roll averaging over terrain – Bring drill to surface to operate – High stiffness platform to react drilling forces • Skid steering – Reduced actuation – Increased stiffness • Thermal approach – Utilize heat from radioisotope power supply – Shunt excess heat to radiator surface CMU | 13 December 2007 19

Vehicle requirements • Drill dominated design – Bring drill to surface to operate – High stiffness platform to react forces • Mobility over rough terrain – 30 cm obstacles – Steep soil slopes • Environments – Fine, abrasive dust – Vacuum, 40 K ground, 3 K sky • Power – Radioisotopic power supply CMU | 13 December 2007 20

NORCAT coring system • 1 meter drilling, sampling & processing system – Lab R&D maturity • Specs – – • Operations: – – – • ø 30 cm borehole ø 1. 5 cm continuous core ~50 kg 0. 5 m x 1. 5 m volume Drill to depth Capture core, transfer Meter core into pieces Crush into fines Transfer to oven Issues: – Loads, torques, vibrations – 1500 – 3000 cc cuttings pile CMU | 13 December 2007 21

Drill cuttings CMU | 13 December 2007 22

Potential attributes • Internal actuation: shafts through shoulder & shaft-drive to hubs • Actuated suspension to surmount extreme obstacle or extricate from twist • Space-relevant wheels & tread: design, fab, mount • Hosting more of RESOLVE subsystems • Upscale chassis and body-averaging beam • Thermal isolation of cold drill and warm body CMU | 13 December 2007 23

Nominal ride height CMU | 13 December 2007 24

Nominal ride height CMU | 13 December 2007 25

Nominal ride height CMU | 13 December 2007 26

JPL Sample-Return Rover SRR 1 – 4 -wheel skid, rotary actuated shoulder, differential body pose SRR 2 K – 4 -wheel steering added CMU | 13 December 2007 27