Performance Analysis and Feedback Control of ATRIAS, A 3D Bipedal Robot

This paper develops feedback controllers for walking in 3D, on level ground, with energy efficiency as the performance objective. ATRIAS 2.1 is a new robot that has been designed for the study of 3D bipedal locomotion, with the aim of combining energy efficiency, speed, and robustness with respect to natural terrain variations in a single platform. The robot is highly underactuated, having 6 actuators and, in single support, 13 degrees of freedom. Its sagittal plane dynamics are designed to embody the Spring Loaded Inverted Pendulum (SLIP), which has been shown to provide a dynamic model of the body center of mass during steady running gaits of a wide diversity of terrestrial animals. A detailed dynamic model is used to optimize walking gaits with respect to the Cost of Mechanical Transport (CMT), a dimensionless measure of energetic efficiency, for walking speeds ranging from 0.5 [s ] to 1.4[ m s ]. A feedback controller is designed that stabilizes the 3D walking gaits, despite the high degree of underactuation of the robot. The 3D results are illustrated in simulation. In experiments on a planarized (2D) version of the robot, the controller yielded stable walking.