Principles in plant roots enable robotic self-anchoring

Plants require no above-ground reaction force to burrow deep underground, using several key principles that could help enable robotic burrowing. 1) Tip extension allows skin friction to counter resistive forces. 2) Root hairs increase anchoring through friction and local interactions. 3) Angled branches increase anchoring force and reduce reaction force. And 4), radial expansion increases soil loading and anchoring force. In our study, we have developed a soft, pneumatic device capable of all four of these plant-inspired behaviors. Tip extension is achieved by a thin-walled tube, inverted back inside itself. When pressurized, it everts and extends from its tip. Flexible root-hair-like protrusions are attached along its skin that passively deploy as the device grows. Branching is done with an array of separate anchors, and radial growth is achieved with nested devices. Our preliminary results on a 1 cm diameter device with 5 mm long protrusions show that combining these principles enables self-anchoring, where the device needs little to no external reaction force to burrow 15 cm or more into granular media. This could be useful in reduced gravity environments where reaction forces are difficult to produce.