Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Rover Chassis

Life in the Atacama Design ReviewDecember 19, 2003

Stu Heys, Dimi Apostolopoulos

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Description and MotivationA new rover chassis for mobility and science is to replace Hyperion in the upcoming campaigns

That is motivated by the need to•Accommodate various science instruments•Improve mobility especially in inclined terrain•Optimize propulsion subsystem

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Key Requirements & Design Drivers• Provide unobstructed FOV and necessary actuated motions for science payloads

• Modify wheel design to improve terrainability• Increase wheel torque to improve slope climbing• Increase rover speed to decrease traverse times• Eliminate drivetrain hysteresis to improve control

• Minimize mechanical complexity. Maintain as much of Hyperion’s design as possible

• Design for 150 kg GVW

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Building on Hyperion’s CompetenciesHyperion New Rover4 driven wheels, brushless DC Same

Chain drive 5+ cm hysteresis in drive system

Coaxial drive zero hysteresis, fewer parts

1 degree of steer motion 3.5m turn radius

2 symmetrical degrees 2.5m turn radius

1 degree of roll freedom inconsistent performance over rough terrain chassis receives direct shocks from bumps

2 degrees of roll with averaged chassis chassis somewhat isolated from shocks each wheel performs identically in rough terrain

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

New Rover Configuration

Steer and roll articulation at front and rear

Pan and tilt unit base atop forward leaning mast

~2.3m2 solar array

Fluorescence imager location .85m range of motion

~.32m3 electronics enclosure roughly equal in volume to Hyperion

Drivetrain completely enclosed by axle structure

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Steering & Articulation

Chassis averages as front tire climbs 30cm obstacle

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Evaluation of Steering Geometries

Metrics -2 to 2 (0 for Hyperion) weightingexplicit front

double passive coupled notes

# actuators 2 -1 -2 0 0mech complexity fab 3 -2 -6 -1 -3

assbymaint

turning radius 1 1 1 2 2 schematicnav cam location 2 -1 -2 0 0req s/w mod nav stereo 3 -1 -3 0 0

controller 3 -1 -3 -1 -3stability 3 1 3 -1 -3 20 degree, 15 cm obstexpected mass 2 -1 -2 -1 -2 analysisexpected power 2 0 0 1 2payload accomodation ease of solar panel 2 0 0 0 0

e box 1 1 1 0 0science intergration 2 1 2 -1 -2 schematic

ease of dead rec 3 -1 -3 1 3agility 1 0 0 1 1failure modes 2 -2 -4 -1 -2heritage 1 -2 -2 -1 -1

weighted weightedtotal -8 -20 -2 -8

LITA 04 Configuration matrix - 10/16/03

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Linear table spans frame members, supports fluorescence imager

Sensor & Solar Panel ConfigurationSub panels slide out of frames with integrated electrical connections

Panels fold up for easy access to e-box and science instruments Science instruments

isolated from vehicle controls

Electronics box nestled between frame members

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Technical Approach•Prototype chassis roll mechanism•Tune-up controller to optimize mobility•Utilize test results to finalize detailed design of axles and pivots•Define volumetric and instrument functional requirements•Finalize sensor placement configuration•Detail design chassis for optimal accommodation of the solar panels,

electronics and science instruments•Design mechanism for fluorescence imager and pan/tilt unit•Integrate prototype instrument deployment mechanism on Hyperion

FEA results for axle

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Design & Implementation IssuesComplex Integration•Science payloads (esp. fluorescence imager)

•2+ degree of freedom•Mast (in-house pan & tilt design)

•Design for 4+ cameras•Solar panels

•Optimized for cell size while avoiding wheel interferences

•Plow•Tricky deployment issues