Control of a Bow Leg Hopping Robot

Abstract

The bow leg hopper is a new design for a locomoting system with a resilient, flexible leg. It features a passive stance phase and natural pitch stability. It is controlled with actuators that configure the leg angle and stored leg energy during flight. During stance, the actuators are mechanically decoupled from the leg and the stored energy is released. The trajectory is determined by the spring-mass physics and the state of the leg at impact. This design casts the controller as a function mapping three trajectory parameters to two control outputs once every hopping cycle. Our particular solution uses a combination of graph-search planning and feedback control. The planner searches to find sequences of foot placements and computes control outputs using numerical solution of a physical model. Feedback control is computed once per bounce. Experimental data from a planar prototype are included demonstrating navigation of simple artificial terrain.