Control of a two-link robot to achieve sliding and hopping gaits

A new example of a hopping robot is considered, consisting simply of two links (the end of one link acts as the foot) joined by an actuated, revolute joint. For the stance phase a nonlinear controller is derived that maintains the balance of the robot and periodically accelerates the center of mass vertically. For large enough oscillations the robot can slide or take off. If flight is achieved, the drift caused by non-zero angular momentum can typically be cancelled by rotating the actuated joint an integral number of times, and the robot can land in the same configuration in which it took off. This is due to the holonomy of a single rotation of the actuated joint. Results of simulations are presented in which the robot achieves both sliding and hopping gaits