Anisotropic Forces for a Worm-Inspired Digging Robot

Digging through granular media is a challenging problem largely because researchers have limited understanding about how granular intruders interact with granular material. In this work, we designed a bioinspired soft digging robot inspired by polychaete worms (or bristle worms) that used reciprocal elongation and contraction to dig through granular material. Our study investigated the use of asymmetric features for producing anisotropic friction to achieve directed motion. Setae-inspired flexible structures and "terra"foils (i.e. surfaces for robot locomotion in sand) were attached to the robot to produce forward movement and to keep the robot submerged under the granular media, respectively. The robot was actuated by four air-powered longitudinal muscles enabling the robot to extend 24% of its body length when actuated at 138 kPa (20 psi). Our bioinspired robot dug forward under 4 cm of particles and turned on the top surface 24 degrees relative to the longitudinal axis of the robot after 60 seconds. This work represents a step towards worm-inspired subterranean robots that can effectively navigate through granular media.