Quantifying disturbance rejection of SLIP-like running systems

Abstract

The speed and maneuverability at which legged animals can travel across rough and cluttered landscapes has provided inspiration for the development of legged robots with similar capabilities. Researchers have developed a number of robots that can run over rough terrain, but there is currently no universally accepted measure for stability in an unstructured environment. This paper considers the effectiveness of a number of stability metrics in predicting the disturbance-rejection behavior of three spring-loaded inverted pendulum (SLIP)-like systems ranging from simple reduced-order models to a one-legged mechanical hopping robot. We show that the gait stability norm utilizing leg-centric indicators and a two-step decay ratio utilizing body-centric indicators provide the best correlation between step response behavior and how the systems perform when running over unknown, uneven terrain. By providing a cross-platform stability comparison, this paper facilitates the development and evaluation of robots and control schemes, such as the active energy removal approach utilized in this paper, that aim to improve the stability of running systems.