Instantaneous control of a vertically hopping leg's total step-time

The main contribution of this paper is a new step-time controller for a vertically hopping robot leg capable of meeting a demanded step-time instantaneously, meaning within a single hop. The ability to perform hops of an arbitrary and changing size accurately forms the motivation behind the work done here. This would allow control of a running robot's foot placement and thus fast traversal of terrain with limited safe foot placement spots. In this paper, the hopping controller is developed and validated using an articulated, hydraulically actuated leg from the HyQ robot which has been modified to include an elastic foot and constrained to hop vertically. It is shown that instantaneous control over the step-time can be achieved using only joint positions and ground contact senses. This was achieved with a simple feedforward lookup in combination with a proportional and integral action.