Effects of lateral undulation in granular medium burrowing with a peristaltic soft robot

Lateral undulation is essential for limbless animals to interact with their environment and facilitate their travelling wave motion. The earthworm uses bending of its body and tip to reduce environmental compaction, anchor itself, and create space for burrowing. In this study, we designed and developed a burrowing soft robot for peristaltic locomotion by observing the lateral undulation behavior at the earthworm's anterior region. To achieve this, we utilized two different soft actuator modules. The tip modules performed lateral undulation and elongation, while the rest of the actuator modules facilitated axial elongation and passive contraction. We characterized the actuator's performance in terms of lateral bending angle, elongation displacement, and penetration force when the tip module interacted with granular media for three different cases: static, tip undulation, and tip elongation. Based on the findings of this characterization, we conducted locomotion experiments with three different gait patterns: tip undulation, tip undulation with elongation, and tip elongation, to evaluate the penetration force and behavior of the peristaltic soft robot when moving in granular media. The results show that tip undulation enhances the locomotory performance of the peristaltic soft robot.