Meeting Abstract

147.5  Monday, Jan. 7  Using Terradynamics to Understand the Role of Limb Morphology in Legged Locomotion on Granular Media ZHANG, T*; LI, C; GOLDMAN, DI; Georgia Institute of Technology; University of California, Berkeley; Georgia Institute of Technology tingnan1986@gatech.edu

The theories of aero- and hydrodynamics form the bases for prediction of animal movement and device design in flowing air and water. For example, they allow computation of lift, thrust, and drag on wings and fins of a diversity of shapes and kinematics in a variety of flying and swimming animals. In contrast, we know little about how limb morphology and kinematics affect legged locomotion on natural substrates like sand and gravel which also flow in response to movement. This is largely because predictive models for such flowing ground have been unavailable. Our recently developed “terradynamics” (Li et al, in review)—predictive force laws for legged locomotion on granular media (sand)—allow us to begin to investigate the role of limb morphology in locomotor performance on granular media. Using terradynamics, we develop a multi-body dynamic simulation of a small six-legged robot (13 cm, 150 g) moving on granular media, and predict the speed of the robot for c-shaped legs of a range of curvatures (-1/R < 1/r < 1/R, where 2R = 4.1 cm is maximal leg length) and a range of stride frequencies (0 < f < 5 Hz). Our simulation reveals that the robot moves faster using positive curvature legs than negative curvature legs, because the former’s leg elements can access larger stresses and penetrate less deeply but generate larger thrust given the same average lift (robot weight). Further, our model predicts that using an optimal c-shaped leg of curvature 1/r = 0.86/R, the robot can achieve maximal speed of ~70 cm/s (~5 BL/s) at 5 Hz. Our study demonstrates the power of terradynamics in the design of bio-inspired devices and promises to aid understanding of the functional morphology of sand-dwelling organisms.