Robust Gait Design Insights from Studying a Compass Gait Biped with Foot Slipping

Abstract

Most current bipedal robots were modeled with an assumption that there is no slip between the stance foot and ground. This paper relaxes that assumption and undertakes a comprehensive study of a compass gait biped with foot slipping. It is found that slips are most likely to happen near impact for a broad range of gaits. Among these gaits, ones with a backward swing foot velocity relative to the ground just before touch down generally require less friction to maintain stable walking than ones with a forward relative foot velocity. Moreover, a larger percentage of gaits with the "swinging backward" foot can tolerate some slipping without falling than those with a swinging forward foot at touch down. Thus, a gait with the swing-backward foot just before touch down should be more robust in the sense of preventing slipping and falling. It is further shown that only one parameter in gait design determines the swing-backward feature, which can help design robust gaits. Models with varying physical parameters such as mass, leg length, and position of center of mass (CoM), are also studied to validate the generality of the results.