Energetic effects of reaction wheel actuation on underactuated biped robot walking

Inertial actuators, such as reaction wheels, have the potential to improve the stability and robustness of bipedal robots. While the stabilizing capabilities of reaction wheels follow naturally from physical laws, the effects on walking efficiency are less clear. This work examines those effects by comparing energy-optimal periodic gaits for a variety of under-actuated, five-link planar biped configurations. When energy consumption is normalized by total mass, bipeds equipped with reaction wheels have decreased walking cost compared to unequipped bipeds of the same mass across a wide range of conditions. At speeds equal to or higher than the optimal walking speed, reaction wheels can reduce walking cost by approximately 8%. When walking with large step lengths, reaction wheels decrease walking costs by more than 20% and allow bipeds to take longer steps. Efficiency improvements scale with the momentum capacity of the reaction wheel, but saturate for particularly large reaction wheels.