Learning to steer a locomotion contact planner

The combinatorics inherent to the issue of planning legged locomotion can be addressed by decomposing the problem: first, select a guide path abstracting the contacts with a heuristic model; then compute the contact sequence to balance the robot gait along the guide path. While several models have been proposed to compute such a path, none have yet managed to efficiently capture the complexity of legged locomotion on arbitrary terrain. In this paper, we present a novel method to automatically build a local controller, or steering method, to generate a guide path along which a feasible contact sequence can be built. Our reinforcement learning approach is coupled with a geometric condition for feasibility during the training, which improves the convergence rate without incurring a loss in generality. We have designed a dedicated environment along with an associated reward function to run a classical reinforcement learning algorithm that computes the steering method. The policy takes a target velocity and a local heightmap of the terrain around the robot as inputs, and steers the path where new contacts should be created. It is then coupled with a contact generator that creates the contacts to support the robot movement. We show that the trained policy has an improved generalization and higher success rate at generating feasible contact plans than previous approaches. As a result, this policy can be used with a path planning algorithm to navigate complex environments.