The effect of limb kinematics on the speed of a legged robot on granular media

Chen Li; Paul B. Umbanhowar; Haldun Komsuoglu; Daniel I. Goldman

physics.bio-phMar 29, 2013

The effect of limb kinematics on the speed of a legged robot on granular media

Authors: Chen Li, Paul B. Umbanhowar, Haldun Komsuoglu, Daniel I. Goldman

Organizations: School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA · Department of Mechanical Engineering, Northwestern University, Evanston, IL, 60208, USA · Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA

Abstract

Achieving effective locomotion on diverse terrestrial substrates can require subtle changes of limb kinematics. Biologically inspired legged robots (physical models of organisms) have shown impressive mobility on hard ground but suffer performance loss on unconsolidated granular materials like sand. Because comprehensive limb-ground interaction models are lacking, optimal gaits on complex yielding terrain have been determined empirically. To develop predictive models for legged devices and to provide hypotheses for biological locomotors, we systematically study the performance of SandBot, a small legged robot, on granular media as a function of gait parameters. High performance occurs only in a small region of parameter space. A previously introduced kinematic model of the robot combined with a new anisotropic granular penetration force law predicts the speed. Performance on granular media is maximized when gait parameters minimize body acceleration and limb interference, and utilize solidification features of granular media.

Legged Robotics

Legged robotics studies how robots with legs move, perceive their surroundings, and perform useful tasks across varied terrain.

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May 29, 2009J/K move · Enter open · S save

Sensitive dependence of the motion of a legged robot on granular media

Chen Li, Paul B. Umbanhowar, Haldun Komsuoglu, Daniel E. Koditschek+1

School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 · Department of Mechanical Engineering, Northwestern University, Evanston, Illinois 60208 · Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, PA 19104

Granular Terrain Locomotion Robot Locomotion Legged Robotics

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Legged locomotion on flowing ground ({\em e.g.} granular media) is unlike locomotion on hard ground because feet experience both solid- and fluid-like forces during surface penetration. Recent bio-inspired legged robots display speed relative to body size on hard ground comparable to high performing organisms like cockroaches but suffer significant performance loss on flowing materials like sand. In laboratory experiments we study the performance (speed) of a small (2.3 kg) six-legged robot, SandBot, as it runs on a bed of granular media (1 mm poppy seeds). For an alternating tripod gait on the granular bed, standard gait control parameters achieve speeds at best two orders of magnitude smaller than the 2 body lengths/s (

\approx 60

cm/s) for motion on hard ground. However, empirical adjustment of these control parameters away from the hard ground settings, restores good performance, yielding top speeds of 30 cm/s. Robot speed depends sensitively on the packing fraction

φ

and the limb frequency

ω

, and a dramatic transition from rotary walking to slow swimming occurs when

φ

becomes small enough and/or

ω

large enough. We propose a kinematic model of the rotary walking mode based on generic features of penetration and slip of a curved limb in granular media. The model captures the dependence of robot speed on limb frequency and the transition between walking and swimming modes but highlights the need for a deeper understanding of the physics of granular media.

Abstract

Legged Robotics

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