Humanoid Balancing on Unstable Terrain Using Whole-Body Momentum Control and Series Elastic Actuation

This video presents early results for dynamic balancing on unstable terrain using THOR, a 34-DoF torque-controlled humanoid. The proposed stance controller stabilizes the centroidal dynamics by regulating the Divergent Component of Motion (DCM) using whole-body momentum control. A quadratic program (QP) is used to compute optimal joint torques given desired task-space objectives and frictional contact constraints. Joint setpoints are tracked using "simple" impedance control to enable compliant balancing on uneven and non-stationary surfaces. High fidelity force control is made possible through the use of low impedance series elastic actuators in the lower body. We test THOR's ability to recover from disturbance forces and track desired DCM reference trajectories during stance. We also demonstrate balancing on unstable terrain using a platform that rotates and translates about a pivot.