This paper emphasizes reliability in designing controllers to enable a blind, modular series-elastic hexapod robot to autonomously navigate (climb over) obstacles such as steps and curbs. Specifically, we suggest that it is not only important to limit the complexity of controllers, but also to limit the number of operating controllers to reduce potential failure points. As such, this paper presents a two-tiered control scheme with a high-level behavioral and a mid-level, modified admittance controller. The behavioral controller, based on a dynamical systems approach, is easy to implement - it is modelless, and may be realized using only analog circuitry. At its core, two oscillators coordinate the phasing of the robot's legs in open loop for nominal locomotion and climbing behaviors. A simple bistable dynamical system accepts torque feedback to decide the active mode and smoothly transition between behaviors - an alternating tripod gait for nominal walking and a quadrupedal gait in climbing mode. Finally, the mid-level, modified admittance controller naturally generates discrete motions as a byproduct of regulating compliant interactions. The proposed controller avoids unnecessary complexities that would be required in switching between discrete motion controllers or primitives in a state machine. It allows the robot to adapt to different obstacle heights while minimizing open parameters.
['Matthew J. Travers', 'Alex Ansari', 'Howie Choset']
A dynamical systems approach to obstacle navigation for a series-elastic hexapod robot