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.