Circumnutations as a penetration strategy in a plant-root-inspired robot

In this paper, we present a study on peculiar plant root movements, named circumnutations, adopted by plants as an efficient strategy to penetrate the soil and implemented in robotic roots to improve their performance in exploration tasks. The robotic root is able to bend and interact with soil owing to a soft actuation mechanism based on the translation of rotary to linear motion by means of helical compression springs. The robotic root integrates a stimulus-oriented behavior combined with circumnutation movements, which leads to an extraordinarily large reduction (more than 80 times) of the force needed for penetration in artificial soil (sawdust) while performing circumnutations with respect to a straightforward movement.