Material remodeling on granular terrain yields robustness benefits for a robophysical rover

Planetary rovers face the risk of entrapment during extraterrestrial exploration; these risks led NASA JSC to develop RP-15, a 300 kg rover capable of lifting and sweeping each wheel to execute a crawling behavior to escape entrapment. We created a miniature rover (2.1 kg) as a robophysical model of RP-15 and conducted systematic and automated experiments in a tilting bed containing a model granular medium (poppy seeds) to discover gaits which allow progress in various conditions. A combination of stepping, paddling, and wheeling (“RS gait”) allows climbing of loose granular slopes. The RS gait produces up to 4x greater tractive (drawbar) forces than wheel rotation alone on dry granular media. Drawbar results were validated through experiments on RP-15 at JSC. On slopes near the maximum angle of stability, a different gait used the front wheels as agitators while paddling the rear wheels to climb granular slopes successfully via controlled avalanching. While substrate disturbance typically hinders granular locomotion, using appropriate active granular reconfiguration can create localized granular structures that facilitate effective locomotion.