Meeting Abstract

12-1  Thursday, Jan. 4 08:00 - 08:15  Snakes Traversing Large Step Obstacles: Kinematics and Mechanics MITCHEL, TW*; GART, SW; KIM, JS; CHIRIKJIAN, GS; LI, C; Johns Hopkins University

Snakes are robust locomotors and commonly traverse a range of obstacles with different topological and frictional properties such as damp rocks or dry logs. Previous studies highlighted the critical role of anisotropic frictional forces in snake locomotion on flat ground. However, our understanding of the mechanics of snake locomotion is more limited in complex 3-D terrains due to a lack of a whole body kinematic description of motion. Here, we study the kinematics and mechanics of the variable kingsnake (L. mexicana) traversing high step obstacles up to 14 body length (L). We applied a recently developed method to quantify continuous body kinematics in 3-D. This allowed us to apply a planar force model (Hu et al., 2009) to calculate frictional forces on the parts of the body in contact with the terrain and inertial and internal forces along the entire body. We found that frictional and internal forces (Ff, Fint ~ 10-4 N/m) during movement were an order of magnitude greater than the inertial force acting on the animal (Finer ~ 10-6 — 10-5 N/m). This suggested that the animal moved nearly quasi-statically and that forces were transduced directly to velocities rather than accelerations, similar to previous observations on flat ground. When climbing onto a step, the animals used the anterior body to pull and the posterior body to push itself. Forward frictional forces in the direction of the snakes’ motion were produced at bands of ground contact (Lcont ~ L10) that propagated down the body from head to tail, with an average contact time of half a second and temporal frequency of 1.6 Hz. Our study suggested that animals modulate body kinematics to use anisotropic friction to traverse 3-D obstacles, and provides guidance for snake-like robots to traverse terrains such as building rubble and landslides.