Meeting Abstract
Snakes exhibit effective limbless locomotion in a diversity of terrains, and many species excel at moving across granular media, a complex and yielding substrate that exhibits both solid and fluid-like behavior. In a previous study, the locomotion of 30 species of snakes, including 18 species of pit vipers, was examined on a granular medium (Marvi et al 2013 Science). While other taxa all moved effectively on level sand (regardless of native habitat type) and most moved effectively on 10 and 20 degree inclined sand (max angle of stability = 28 degrees), 25% of the pit vipers produced minimal displacement on horizontal sand, and almost all failed on inclined sand. To understand the role of interactions between the body surface and the granular media in determining success or failure of snakes on granular media, we performed systematic locomotor experiments using a robot snake using different undulation strategies at various inclines, which allowed for precise control of friction and undulation strategy. The robot consisted of ten servomotors in 3D-printed shells oscillating in a sine wave with a maximum bend angle, with each motor having a phase offset relative to the prior. High overall skin friction resulted in minimal displacement, whereas, with low friction, success was dependent on the angle between joints and the number of waves on the body. Decreasing the ratio of parallel and perpendicular forces via a ventral ridge improved performance across most undulation strategies. This suggests an important influence of body surface on limbless locomotion through granular media, and highlights the importance of the interaction between snake skins and granular media.
