Body-leg coordination for effective obstacle traversal

Large, slippery obstacles can present great challenges for ground robots. Recent studies have shown that small, legged robots can strategically exploit leg-obstacle interacting force to traverse densely distributed obstacles. Here we investigate how body-leg coordination impacts such obstacle-aided locomotion. We study a quadrupedal robot with a pitching spine traversing half-cylindrical obstacles. The robot performs a bound gait, where the front legs move synchronously and alternate with the rear legs. The spine oscillates ±60 degrees, with the same stride period as the legs but lagging the front legs by a phase offset, Φ_FB. Experiments show that robot locomotion performance depends sensitively on Φ_FB, achieving a large stride length of 0.42 body length per stride cycle at Φ_FB = 0.3 and 0.7, but near-zero displacement elsewhere. Tracking data revealed that successful obstacle traversability arises from effective leg-obstacle anchoring. At high-traversability Φ_FB, the front legs reach forward as the rear legs anchor to the obstacles, then, as the body folds inward, the front legs anchor and pull the rear legs forward. These results highlight the importance of body-leg coordination for exploiting terrain interactions.