In this paper, we present our approach to achieve autonomous walking over complex terrain on the quadrupedal robot, LLAMA. LLAMA is a prototype robot designed by NASA Jet Propulsion Lab as part of the Army Research Laboratory’s Robotics Collaborative Technology Alliance. One of the major objectives of this robot is to be capable of traversing complex terrain autonomously to enable operating alongside a human squadron. This goal requires the robot to be capable of identifying practical footholds according to the environment, which may be sparse, and using these for walking. To accomplish this end, we first introduce two new contact planners. One is based on either desired body path plans; the other an A* graph-search based planner that find contacts over rough terrain given the environmental constraints. We then plan a dynamic trajectory using a custom Divergent Component of Motion planner, which is tracked using a whole-body inverse-dynamics control framework. We also introduce new methods for maintaining balance by adjusting step position and timing. We additionally discuss our approach for contact detection without the use of force sensors. We highlight the results in several experiments, both in our laboratory and at the RCTA Capstone Event at the Camp Lejeune Marine Corps base. We conclude with a discussion of these results, specific implementation problems, and lessons learned when developing such a control architecture on a quadruped.
