Waypoint-seeking using head orientation during burrowing in dry granular media

Researchers continue to study the mechanisms behind controlling and maintaining depth for subterranean robotic locomotion. Prior work, inspired by the sandfish skink (Scincus scincus), demonstrated that fixed discrete head shapes influence lift force and, as a result, two-dimensional movements of a robophysical model submerged and moving in a granular substrate. Our work thus far modulates head orientation throughout a single burrowing period to produce desired trajectories in the vertical plane. We tested whether such head reorientation supports closed-loop depth control, and we studied the effect of head shape on this ability. Substantial variation in trajectory emerged across head orientations and shapes, and open-loop control of trajectory using head angle was not adequate to perform precise movements, even in homogeneous granular media. However, closed-loop control of head angle does allow a burrower to achieve a deeper objective target location with position feedback, so long as the head is shaped appropriately for the objective–more pointed snouts provide more rapid downward trajectories. We now test additional waypoints to further characterize the benefits and drawbacks between different shapes, anticipating that a more blunt snout provides smoother trajectory control. This work provides insight on applying morphology-driven locomotive behaviors to develop closed-loop steering capabilities of burrowing robots underground.