High-speed and energy-efficient collisionless walking of underactuated rimless wheel

This paper discusses a method for achieving high-speed collisionless walking of a point-footed walker. First, we introduce a model of an underactuated rimless wheel with an internal reaction wheel for analysis, and develop two controllers for the single-limb support and double-limb support phases so that they minimize the corresponding control period based on the principle of the minimum-time control. The former is determined under the unilateral constraint condition, whereas the latter is determined under the constraint condition of the zero-moment point for maintaining double-limb support, respectively. Second, we extend the results obtained for generation of the highest speed collisionless walking gait without including double-limb support phases by appropriately setting the initial angular velocity of the reaction wheel. The approximate analytical solution of the target initial angular velocity is derived using the linearized model, and that of the nonlinear model is numerically obtained using a bisection method. The validity of the proposed methods is investigated through numerical simulations.