Gait design and mechanical intelligence facilitate open-loop limbless obstacle aided locomotion

Limbless organisms, such as snakes and nematodes can exploit interactions with obstacles to enhance their mobility. This is referred to as obstacle-aided locomotion (OAL) and we posit can be robophysically modeled as a coordination of high-level self-deformation patterns (referred to as gait templates) alongside low-level adaptations of the body to diverse environmental conditions. In robotics, previous research on OAL has predominantly employed stereotyped traveling-wave gait templates (circular trajectory in the shape space) and active body deformations based on sensory feedback for obstacle navigation. In this work, we test the efficacy of elliptical gaits in OAL, using geometric mechanics to generate novel undulatory templates. By converting the body-obstacle contacts in the position space into constraints on lateral and rotational movements in the robot shape space, we discover that elliptical gait templates can generate greater forward thrust through interactions with a single post. When we implement the elliptical gait templates on a bilaterally actuated cable-driven limbless robot, we verify in robophysical experiments that, 1) the anisotropic compliance can enable the robot to move through lattices without the need of actively changing body control; 2) elliptical gaits with higher eccentricity excel in environments with lower obstacle density while lower eccentricity elliptical gaits are preferable in environments with higher obstacle density.