The Energetic Benefit of Robotic Gait Selection—A Case Study on the Robot RAM<italic>one</italic>

Abstract

Should a legged robot use different gaits at different desired speeds? If so, what constitutes these gaits? This work examines these questions through a case study on the planar bipedal robot RAMone. Using a realistic model of the robot, this paper presents the outcome of a series of trajectory optimizations which minimize the electrical cost of transport and find the associated optimal motion strategies. These optimizations show that at low speeds it is most economical to perform a ballistic walking gait with an instantaneous transfer of support. At higher speeds, spring-mass running with an extended air-phase becomes the optimal gait. Additionally, it is illustrated that the optimal running gait is conducted with the knee joints pointing away from rather than towards the direction of travel. The transition between ballistic walking and spring-mass running happens at a speed of 1.04 m/s, and switching can reduce energy expenditure by up to 259%.