They found that blocks with leading edges that formed angles with the horizontal plane less than 80 degrees generated positive lift forces and wedges with leading edges greater than 120 degrees created negative lift. With leading edges between 80 and 120 degrees, the wedges did not generate vertical forces in the positive or negative direction.
Using a numerical simulation of object drag and building on the group’s previous studies of lift and drag on flat plates in granular media, the researchers were able to describe the mechanism of force generation in detail.
“When the leading edge of the robot head was less than 90 degrees, the robot’s head experienced a lift force as it moved forward, which resulted in a torque imbalance that caused the robot to pitch and rise to the surface,” explained Goldman.
Since this study, the researchers have attached a wedge-shaped head on the robot that can be dynamically modulated to specific angles. With this improvement, the researchers found that the direction of movement of the robot is sensitive to slight changes in orientation of the head, further validating the results from their physics experiments and computational models.
Being able to precisely control the tilt of the head will allow the researchers to implement different strategies of head movement during burial and determine the best way to wiggle deep into sand. The researchers also plan to test the robot’s ability to maneuver through material similar to the debris found after natural disasters and plan to examine whether the sandfish lizard adjusts its head inclination to ensure a straight motion as it dives into the sand.