Obstacle Modulation of Legged Robot Dynamics

Legged robots have unique capabilities to negotiate obstacles. However, due to limited understanding of the complex interactions between robot legs and obstacles, many legged platforms circumnavigate obstacles to avoid large force disturbances. Our study aims to provide physical understanding of complex robot-obstacle interactions, enabling multilegged robots to exploit environment shape and generate desired dynamics by properly coordinating leg movements. With a previously characterized dependence of obstacle reaction force on contact position, we develop a predictive model that captures robot dynamics by considering obstacles as a superposed force field. We predict and empirically demonstrate the existence of asymptotically stable yaw angle equilibria in the horizontal plane dynamics of a quadruped robot running over periodically spaced “logs” (cylindrical obstacles). As obstacle spatial period is varied, a bounding robot maintains its stable equilibrium state at a yaw angle of 0^○ (perpendicular to the logs), whereas a trotting robot exhibits transitions to yaw angle equilibria of ±θ^○ (0^○ < θ < 90^○). We show that θ can be predicted using the characteristic length of the robot gait and the environment spatial period.