Continuous Skin Eversion Enables an Untethered Soft Robot to Burrow in Granular Media.

Exploration in environments that are too hazardous or inaccessible to humans is one of the most promising uses of robotics. In particular, natural environments that contain granular media present a variety of challenges for the design and control of robots. Recently, everting vine robots have been demonstrated that can navigate many different environments, including digging in sand. However, everting vine robots typically rely on a tether which limits their ability to explore. Here we present an untethered, continuously everting soft robot for exploration in granular media. We test the ability of this design to reduce the drag on the robot while moving through granular media. We then investigate design features to improve the ability of the robot to generate thrust in granular media, and validate them experimentally. Finally, We test our robot's ability to locomote and dig.