Advantages of slanted grousers for skid-steer planetary rovers with rigid wheels

Abstract

Lunar exploration activities around the world are driving development of low mass skid-steer rovers, for which rigid wheels with grousers are common. Wheels with slanted grousers (i.e. that span from the inner to the outer edge of the wheel surface at an angle, rather than directly across) are compared favorably in this work against V-offset shaped grousers in skid-steer point turn performance, without any reduction in slope climbing performance. Single wheel tests are conducted in GRC-1 lunar simulant with the wheels oriented along a representative slip angle corresponding to skid-steer point turning. Slanted grousers achieve positive tangent turning force, $F_T$, a metric introduced to identify conditions when a wheel can sustain skid-steer point turning. The slanted grouser achieves a positive $F_T$ at slip ratios below 0.4 compared to as much as 0.6 for V-offset, while also only experiencing approximately half as much sinkage. On the other hand, there is little to no difference in performance in straight line driving, relevant for nominal driving and slope climbing. Full rover tests with 4 appropriately configured slanted grouser wheels validate point turn and slope climbing performance with an average skid-steer point turn slip ratio of approximately 0.35 and 0.8 for slope climbing.