Force Redistribution in a Quadruped Running Trot

In this paper, an attitude control strategy is developed for a high-speed quadruped trot. The forces in the trot are redistributed among the legs to stabilize the pitch and roll of the system. An important aspect of the strategy is that the controller works to preserve the passive dynamics of quadruped trotting that are accurately predicted by the spring-loaded inverted pendulum (SLIP) model. A hybrid control strategy is presented which allows the quadruped to reach a speed of 4.75 m/s and turn at a rate of 20 deg/s in simulation under operator control. The discrete part of the controller runs once per trot step and outputs a stance thrust energy and hip angles for touchdown. The stance thrust energy accounts for losses during the step, especially at touchdown. Both the stance thrust energy and hip angles dictate the natural dynamics during stance. The force redistribution algorithm continuously operates during stance to stabilize the body's tilt axes, roll and pitch, with minimal effect on the prescribed natural dynamics. The 1.0 m/s increase in speed over previously presented work is largely due to the more dynamically-consistent force redistribution algorithm presented in this paper. The controller also tracks desired changes in heading, for which the biomimetic method of banking into a high-speed turn is also realized.