Coordination of back bending and leg movements for quadrupedal locomotion

Many quadrupedal animals use lateral degrees of freedom in their backs to assist locomotion. This paper seeks to use a robotic model to demonstrate that back bending assists not only forward motion, but also lateral and turning motions. We present a simple planner that uses geometric mechanics to prescribe gaits that coordinate both leg movements and back bending motion. Using these geometric tools, we show that back-bending can improve stride displacement in the forward, rotational, and lateral directions. Interestingly, we observe that the animal’s (salamander, Salamandra salamandra) back-bending is close to our calculated back-bending to improve forward displacement. In addition to locomotion performance improvement, back bending can also expand the target position space a robot can reach within one gait cycle. Our results are verified by conducting experiments with a robot moving on granular materials.