Motion planning for quadrupedal locomotion: coupled planning, terrain mapping and whole-body control

Legged robots promise an advantage over traditional wheeled systems, however, most legged robots are still confined to structured and flat environments. One of the main reasons for this is the difficulty in planning complex whole-body motions while taking into account the terrain conditions. This problem is very high-dimensional as it considers the robot’s dynamics together with the terrain model in a suitable problem formulation. In this work, we propose a novel trajectory and foothold optimization method that plans dynamically both foothold locations and motions (coupled planning). It jointly optimizes body motion, step duration and foothold selection, considering the terrain topology. We show that it can be easily generalized to various terrain conditions (i.e. through the terrain costmap), thanks to a parametrized dynamic model, and an online terrain mapping that is used in our real-time wholebody controller. Our whole-body controller tracks compliantly trunk motions while avoiding slippage, as well as kinematic and torque limits. For the sake of analysis, we compare our coupled planner with our previous decoupled planner. With this novel locomotion framework we can cross a wider range of terrain conditions. We report thorough experimental results and comparative evaluations over a set of terrains of progressively increasing difficulty.