UC Berkeley

Sand traps are a hazard for both Martian and lunar rovers. Conventional drive control methods aim to limit wheel slip without considering the effect that both slippage and sinkage have on the forces generated by a rotating wheel. Sandy terrain models, such as granular Resistive Force Theory (RFT), suggest that mobility can be improved by driving the front and back wheels at different angular velocities according to their differing sinkage depths. In this experiment, the effect of the front-back wheel speed ratio on the rover’s forward velocity is measured while applying a resistance load to imitate the resistance of climbing a slope. The maximum rover velocities occur at front-back wheel speed ratios at or below 1, when the back wheels drive faster than the front wheels, and the benefit of faster back wheel speeds becomes more pronounced as resistance load increases. In the highest resistance scenario with a drawbar pull to weight ratio of 43% (effective slope angle of 24°), the rover velocity increases by 10% when the back wheels are driven 2.5 times faster than the front wheels. In challenging areas of high slip and sinkage, front-back differential drive control has the potential to enable the rover to achieve more efficient traversal without any modification to existing design and control practices.