2D Balancing Controller for a Unicycling Biped via Legged Locomotion

Legged humanoid robots are growing in popularity in the commercial space, so determining how to control legs to achieve dynamic balancing is critical. Previous work has been done on creating robots that can unicycle, but these robots directly actuate the wheel or do not have fully actuated legs. The controller proposed in this work uses a multi-body model consisting of three branched pendulums connected to a wheel. Double pendulums are used to represent the legs while a single pendulum represents the body of the biped joined to the unicycling stand. The model uses anthropometric data to ensure human-like proportions of the leg segments. A linear-quadratic regulator (LQR) was implemented to drive the robotic hip and knee joints such that they would actuate the pedal mechanism of the unicycle. In simulation, we were able to drive the system to balance while pedaling two rotations of the wheel in under 5 seconds. When disturbance torques were applied to oppose the motion, the system was able to recover from a maximum torque of 1.3 Nm applied during its most robust configuration and 0.5 Nm during its least robust configuration, both within 10 seconds of the angular impulse.