Roving Around the Moon and Mars: Active Weight Redistribution and Strategic Slip Control for Augmenting Wheeled Mobility
- Cao, Cyndia Aiyun
- Advisor(s): Lieu, Dennis K;
- Stuart, Hannah S
Abstract
Planetary rovers have a history of entrapment in soft Martian sand, which is difficult to visually anticipate and results in high-stakes extrication efforts. As scientific objectives on Mars evolve and interest in lunar exploration increases, the need to traverse loose, sandy terrain incentivizes the design of more energy-efficient locomotion suspensions and gaits. Traditional rover designers consider wheel sinkage and slippage to be a consequence of vehicle and terrain parameters. However, articulation in suspension kinematics would allow wheel-terrain interaction to be manipulated in more dimensions to improve mobility.
Motivated by wheel-terrain interaction models in sand, specifically granular Resistive Force Theory, this thesis explores how load and slip can be controlled to augment the effectiveness of wheeled rovers. In simulation, dynamic front-back load redistribution using a gyroscopic moment is proposed for climbing tall step-like obstacles. Experiments with the load-responsive suspension controller of the Volatiles Investigating Polar Exploration Rover found that consistent wheel-ground contact was desirable for stability but mobility metrics were insensitive to quasi-static load distribution in nominal operating terrains. Meanwhile, in loose sandy terrain, slip is critical to generate forward traction when wheel sinkage is high. Driving wheels at different speeds to impose relative slip based on wheel load can lead to limited improvements in locomotion; this is an option to explore further for extrication efforts of existing rovers. More significantly, articulated suspensions can directly control wheel slip via the kinematics of the vehicle, and push-pull locomotion combined with controlled wheel slip can lead to faster and more efficient traversal of sink tanks and steep slopes. These works show that there is still significant room to improve traditional wheeled planetary locomotion and that suspensions with a couple additional degrees of control can be deployed robustly while safeguarding against entrapment.