Control of a walking biped using a combination of simple policies

We present a decoupled controller for a simulated three-dimensional biped. To handle the high-dimensionality of the system, we break the dynamics down into multiple subsystems, which we control separately. For both the sagittal and coronal plane dynamics, we use dynamic programming to simultaneously optimize body motion, foot placement, and step timing for a two link inverted pendulum model. To use these simplified policies we map the full state to a simplified state, and then map the control action back onto the full system. The swing leg is controlled via continuously updated desired trajectories. These separate policies are then coordinated by the estimated time until touchdown, which is provided by the sagittal policy. By varying the lean angle or changing the sagittal policy we are able to contol the walking speed. We also evaluate the performance of our controller in terms of robustness to perturbations.