UNC PHYSICS AND ASTRONOMY COLLOQUIUM
Daniel Goldman, Georgia Tech
“Sidewinding on sandy slopes”
Many limbless locomotors inhabit sandy deserts, and the bio and neuromechanical principles by which they move effectively in dry granular media are largely unknown. I will describe progress we have made in understanding limbless locomotion on the surface of granular media through integration of biological, robotic and granular physics experiments. Specifically, we study the locomotion of the Sidewinder rattlesnake (Crotalus cerastes), a snake that uses a peculiar form of locomotion called sidewinding. In this gait, the animal translates through successive lifting of body segments while other segments remain in static (rolling/peeling) contact with the ground. Biological measurements (in collaboration with Dr. Joseph Mendelson, Zoo Atlanta and Prof. David Hu, Georgia Tech) reveal that the snake employs an anti-slip strategy to negotiate granular inclines, increasing contact length as the hill angle increase. Such control allows the animal to ascend surfaces even close to the angle of maximum stability. Implementing the control strategy in a limbless robot (in collaboration with Prof. Howie Choset, Carnegie Mellon University) enables the robot to ascend sandy inclines with comparable ability to the animal. Systematic studies of the robot demonstrate how changes in contact length balance slip and pitch. We rationalize the anti-slip strategy by making the first measurements of localized plate drag on granular inclines. These measurements reveal that the snake’s increase in contact length maintain downhill stresses below the granular yield stress, allowing the snake (and robot) to locomote with little slip at all angles.