Task-level control and Poincare map-based sim-to-real transfer for effective command following of quadrupedal trot gait

The ability of quadrupedal robots to follow commanded velocities is important for navigating in constrained environments such as homes and warehouses. This paper presents a simple, scalable approach to realize high fidelity speed regulation and demonstrates its efficacy on a quadrupedal robot. Using analytical inverse kinematics and gravity compensation, a task-level controller calculates joint torques based on the prescribed motion of the torso. Due to filtering and feedback gains in this controller, there is an error in tracking the velocity. To ensure scalability, these errors are corrected at the time scale of a step using a Poincar ' e map (a mapping of states and control between consecutive steps). A data-driven approach is used to identify a decoupled Poincar ' e map, and to correct for the tracking error in simulation. However, due to model imperfections, the simulation-derived Poincar ' e mapbased controller leads to tracking errors on hardware. Three modeling approaches - a polynomial, a Gaussian process, and a neural network - are used to identify a correction to the simulation-based Poincar ' e map and to reduce the tracking error on hardware. The advantages of our approach are the computational simplicity of the task-level controller (uses analytical computations and avoids numerical searches) and scalability of the sim-to-real transfer (use of low-dimensional Poincar ' e map for sim-to-real transfer). A video is here http: //tiny.cc/humanoids23.