Meeting Abstract

11.1  Monday, Jan. 4  The effects of limb kinematics on the motion of a legged robot on sand LI, C.; UMBANHOWAR, P.B.; GOLDMAN, D.I.*; Georgia Tech; Northwestern University; Georgia Tech chen.li@gatech.edu

Effective locomotion of organisms and physical models of organisms (robots) can require subtle changes of limb kinematics to achieve high performance on different substrates. To develop predictive models for legged devices and to provide hypotheses for biological locomotors, we systematically study the performance (forward speed) of a small legged robot, SandBot, on granular media as a function of stance and swing gait parameters. At fixed limb frequency and volume fraction, speed is sensitive to variations in the gait parameters that control angular onset, angular duration, and temporal duty factor of the stance phase of the limb cycle. High performance occurs only in a small region of gait parameter space. A modified version of an existing kinematic model [Li et. al, PNAS, 2009] predicts the speed, and reveals that performance is maximized when gait parameters minimize limb acceleration and interference to increase interaction with the solid phase of the media. For example, gait parameters that generate fast bouncing motion on hard ground generate much slower motion on sand. Instead, high performance on sand is achieved when the start of the stance phase is advanced to better utilize the asymmetric resistance force produced by rotational penetration of limbs into sand. A similar phase shift is observed in the zebra-tailed lizard, Callisaurus draconoides, when the substrate is changed from hard ground to sand, suggesting that the physics of granular media may constrain animals to employ similar strategies for achieving effective locomotion.