Soft Robotic Locomotion by Peristaltic Waves in Granular Media

Soil exploration is required in many different activities, ranging from detecting minerals or pollutants to finding water sources. Yet, penetrating soil is extremely challenging because of high pressures and friction even in a few centimeters of depth. In nature, earthworms move inside soils by peristalsis, i.e. by wave-like deformation traveling along their entire soft body. Taking inspiration from these animals and understanding their peristaltic locomotion offer interesting solutions for achieving soil exploration. To this aim, we fabricated and assembled a soft robot able to generate controlled and tunable peristaltic deformations. We systematically experimented peristaltic locomotion in a granular medium and compared it to movement on a planar surface. Our results show that locomotion based on peristaltic waves of a soft robot in granular media is possible, generally slower than locomotion on planar surfaces. This helps in reducing friction during the robot penetration in soil. Interestingly, our results also show how the wave patterns and actuation frequency differently influence the speed and the direction of movement in the different media, providing guidance in developing future soft robots for soil exploration.