Soft Robot Actuation Strategies for Locomotion in Granular Substrates

Abstract

Soft-bodied organisms such as annelids may exploit body compliance using their hydrostatic skeletons and muscles to burrow in granular substrates. In this letter, we investigate the design of soft digging robots inspired by the bristled worm, (polychaetas). The behavior of soft structures in dry granular environments is complex and still not well understood. We describe the design and fabrication of a soft robot capable of locomotion in granular substrates and investigate actuation strategies for drag reduction inspired by the bristled worms biomechanical behaviors. The drag reduction experiments focus on an actuated soft leading segment. We implemented and studied two methods of actuation for the leading segment: periodic radial expansion and bi-directional bending, both of which we find to have an impact on the locomotion in granular substrates. Soft robots performing periodic radial expansion of the leading segments experienced the least overall drag force, while those with unactuated tips experienced the largest drag force, emphasizing the importance of controlling the tip stiffness to enable effective subsurface movement. Based on these results, we designed and tested a tethered, three-segment soft robot capable of digging through dry granular media.