A Physical Model and Control Strategy for Biped Running

Abstract

We are in the process of building a biped robot capable of highly dynamic maneuvers. Implementing such maneuvers in real-time entails heuristic controllers founded on a grasp of the dynamics. We present here an analysis of the mechanics of biped running and a control strategy for stable running. By expounding on the direction of the ground-reaction forces and utilizing an impulse representation of the contact phase, we present a tractable model of the mechanics. This model motivates the control strategy and provides a basis for extending the strategy to more general systems. The control strategy consists of a simple set of three rules, where the key rule considers the leg-length upon liftoff. This rule offers a simple control for both steady-state and accelerated running. We present the equilibrium running index as a characterization of biped running. It relates the parameters affecting running and has broad applicability to biological and robotic systems. The control strategy was verified in simulation and the results are presented.