Bio-inspired rotational penetration and horizontal self-burrowing soft robot

Abstract

Inspired by self-burial seeds and burrowing amphisbaenians, we experimentally explored the effect of rotation on vertical and horizontal penetration resistance in shallow sands; we then integrated the findings with previously identified burrowing principles to design a soft, horizontal burrowing robot. A rotational penetration system was developed by integrating a six-axis robotic arm with custom motorized penetrators and corresponding control and data acquisition units. A series of vertical rotational penetration tests were conducted in Ottawa F65 sand with different vertical and rotational velocity combinations. The effects of relative slip velocity (the ratio between the rotational and vertical penetration velocity, and inertial number (a function of the resultant velocity) were investigated. The results revealed that increase in relative slip velocity led to decrease in penetration force and increase in penetration torque. On the other hand, the inertial number had a negligible effect on the reduction of penetration force: The penetration force and torque levels were comparable under a same relative slip velocity, regardless of the initial number. The rotation-induced reduction in penetration force was further confirmed in the context of horizontal penetration. Furthermore, the results suggested that the reduction in penetration force was also influenced by the embedment depth and the geometry of the penetrators. Based on the findings, a self-burrowing robot was developed by incorporating a rotational tip into a soft linear actuator, and its burrowing behavior in the horizontal direction was preliminarily evaluated. We present these components together with the intention of demonstrating a real-life workflow that we employed in the emerging field of bio-inspired geotechnics.