Abstract: Inspired by the morphology characteristics and the locomotion mechanisms of the earthworm, and the snakes’ morphology characteristics and motivated by the demands for multi-modal locomotion robots in variable working environments, this paper presents a novel bi-modal robot named as Snake-Worm Locomotion Robot (SWL-Robot). Two fundamentally different locomotion mechanisms, the earthworm’s peristaltic rectilinear locomotion and the snake’s lateral undulation, are synthesized in the SWL-Robot design. In detail, the SWL-Robot consists of six earthworm-like body segments interconnected by rotational joints and a head segment equipped with a couple of independently driven wheels. By actuating the segments following a peristaltic wave-like gait, the robot as a whole could perform earthworm-like rectilinear crawling. The robot could also perform snake-like undulatory locomotion driven by differential motions of the wheels at the head segment. To understand the relationship between the design parameters and the robotic locomotion performance, kinematic models of the SWL-Robot corresponding to the two locomotion modes are developed. Rich locomotion behaviors of the SWL-Robot are achieved, including the peristaltic locomotion inside a tube, multiple planar motions on a flat surface, and a hybrid motion that switches between the tube and the flat surface. It shows that the measured trajectories of the SWL-Robot agree well with the theoretical predictions. The SWL-Robot is promising to be implemented in tasks where both tubular and flat environments may be encountered.

Key words: Multi-modal locomotion , · Peristaltic locomotion , · Planar locomotion , · Worm-like robot , · Snake-like robot