Adaptive locomotion on varying ground conditions via a reconfigurable leg length hopper

Abstract

In this paper, we present the concept of adapting to changes in ground conditions like stiffness, damping and friction, using a novel two degree of freedom reconfigurable leg length hopping robot with a fixed passive compliance. In such a robot, the change in the dynamics of the single legged hopper can be induced by the change in coupled stiffness and damping of the system, i.e., stiffness and damping of the ground coupled with the stiffness and damping of the robotic leg. It is experimentally shown by in-place hopping of a robotic leg on various grounds (stiff, less stiff and soft) that the leg can effectively adapt to changes in coupled stiffness and damping by the rate and the amplitude at which the leg length changes. This is true, while the leg hops in-place as the role of ground friction is negligible. However, in forward motion where the ground friction dominates, a change in initial effective leg length, i.e., shortening or lengthening can provide an additional support to the hip motor in overcoming even large variations in ground friction. This is demonstrated through a planar locomotion experiment on different ground surfaces. The overall results provide strong support for this concept.