Crawling on waves with a soft foot*

Snails crawl by generating a sequence of pedal waves via ventral muscle contractions, known as waves, and relaxations termed inter-waves. These actions transfer propulsive forces from a single foot to the ground through a thin layer of mucus secreted by the snail. Inspired by the adhesive locomotion of snails, we have developed a bioinspired soft robot equipped with a single-soft foot. This foot features a network of embedded pneumatic chambers generating various traveling wave patterns, two lateral bending actuators for steering, and distributed fluidic channels for selective artificial mucus deposition. A powerhouse comprised of a compact wireless controller, a pressure sensor, a pump, electro valves, and mucus storage housed in a shell mounted on the soft foot, creating an untethered robot control for robophysical analysis. Here, we show two experimental pathways in analyzing the physics behind snail locomotion. First, we reproduce snail's normal and loping gaits by varying the actuation wavelength and amplitude. Second, through rheological characterizations, we demonstrate that upon actuation, the thin mucus layer between the foot and the substrate creates stress in the layer, leading to adhesive locomotion. Our work integrates soft materials and mucus viscoelasticity to control sliding friction, enabling both direct and retrograde robot locomotion through altering pedal wave direction.