Full Dynamics LQR Control for Bipedal Walking

Biped robots that are expected to locomote in human environments require whole-body controllers that can offer precise tracking and well-defined disturbance rejection behavior. Although walking is a complex dynamical task involving both hybrid dynamics and underactuation, it is unclear the level of complexity needed to generate and execute these tasks. Previously in [4], we experimentally evaluated the use of a linear quadratic regulator (LQR) using a linearization of the full robot dynamics together with the contact constraints for static poses. The advantage of the controller is that it explicitly takes into account the coupling between the different joints to create optimal feedback controllers for whole-body coordination. Additionally, this control policy is computationally light weight and shows a reliable push recovery behavior competitive with more sophisticated balance controllers, rejecting impulses up to 11.7 Ns with peak forces of 650 N. Our preliminary results on balancing were very encouraging and we are now exploring how these results can extend to more dynamic tasks such as walking. The major contribution of this work will be an exploration in the of the amount of complexity needed to create whole-body motions for walking.