Meeting Abstract

147.6  Monday, Jan. 7  Rapid locomotion of a small lizard on sand requires fluid-like ground reaction forces LI, C*; HSIEH, S.T.; UMBANHOWAR, P.B.; GOLDMAN, D.I.; UC Berkeley; Temple Univ.; Northwestern Univ.; Georgia Tech chen.li@berkeley.edu

The desert-dwelling generalist zebra-tailed lizard (Callisaurus draconoides, ~10 cm, ~10 g) uses its large, elongate hind feet to rapidly run (~10 body length/s) on a diversity of substrates ranging from solid rocks to loose sand. In a previous study (Li et al., 2012, J. Exp. Biol.), visible light high speed video showed that during each step on granular media (sand), the lizard’s hind feet slapped on the surface at touchdown and penetrated into the substrate during stance. To explain the observed center-of-mass dynamics, the ground reaction force was assumed to be dominated by speed-independent frictional drag, and it was hypothesized that during stance the hind feet rotate subsurface in the vertical plane to generate lift. Here we use x-ray high speed video to obtain the lizard’s subsurface foot kinematics during running on granular media and confirm the hypothesized foot rotation. However, using granular impact force measurements, a recently developed terradynamics of granular media, and the observed foot kinematics, we find that the combined impact force during initial foot touchdown and speed-independent frictional drag force during foot rotation only account for part of the required lift to support locomotion. This suggests that the rapid foot rotation further allows the lizard to utilize inertial forces from the local acceleration of the substrate (particles), analogous to the basilisk lizard which runs on the surface of water using hydrodynamic forces. Further evidence of inertial-force-dominated propulsion has been found in small lizard-sized robots (~10 cm, ~20 g) running on granular media (Qian et al., 2012, Robotics: Science & Systems).