This paper develops feedback controllers for walking in 3D, on level ground, with energy efficiency as the performance objective. Assume The Robot Is A Sphere (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 (m/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.

An articulated wing structure with a silicon-based skin enables a robot to mimic bat-like flight abilities.

Abstract-This paper presents a feedback controller that allows MABEL, a kneed planar bipedal robot with 1 m-long legs, to accommodate terrain that presents large unexpected increases and decreases in height. The robot is provided information on neither where the change in terrain height occurs, nor by how much. A finite-state machine is designed that manages transitions among controllers for flat-ground walking, steppingup and down, and a trip reflex. If the robot completes a step, the depth of a step-down or height of a step-up can be immediately estimated at impact from the lengths of the legs and the angles of the robot's joints. The change in height can be used to invoke a proper control response. On the other hand, if the swing leg impacts an obstacle during a step, or has a premature impact with the ground, a trip reflex is triggered on the basis of specially designed contact switches on the robot's shins, contact switches on the end of each leg, and the current configuration of the robot. The design of each control mode and the transition conditions among them are presented. The paper concludes with experimental results of MABEL (blindly) accommodating various types of platforms, including ascent of a 12.5 cm high platform, stepping-off an 18.5 cm high platform, and walking over a platform with multiple ascending and descending steps.

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