Penetration Forces of a Rotating Helical Penetrator in Granular Media: Experiments and Insights into the Design of a Burrowing Robot

It has been observed that some organisms such as Erodium seeds, snakes, and sandfish skink can bury themselves in the ground effectively and efficiently. These self-burial behaviors are achieved by one or multiple modes of locomotion including rotation, twisting, and undulation of an asymmetric body. To better understand the fundamental mechanism of these biological burrowing strategies, a series of upward and downward rotational penetration tests were conducted to evaluate the effects of rotational motion, asymmetric shape, and different properties of granular media on the penetration resistance using a robotic arm and 3D printed motorized penetrators. The results confirm that the downward penetration force decreases with the increase of rotational speed and that it further decreases if the penetrator is of a helical shape, highlighting the effects of asymmetric kinematics. It can be concluded that the penetration resistance of a helical penetrator depends on the rotational direction. For a right-handed helical penetrator, clockwise rotation resulted in significantly lower penetration force than counterclockwise rotation and required lower torque, although both reduced penetration force compared to non-rotational penetration. It was found that by coordinating the motions of the helical body, the penetration forces, and anchorage forces can be tuned to achieve self-burrowing.