86.5 Tuesday, Jan. 6 Enhancement of legged robot speed on granular media using kinematics which promote solidification LI, C.*; UMBANHOWAR, P.; KOMSUOGLU, H.; KODITSCHEK, D.E.; GOLDMAN, D.I.; Georgia Insitute of Technology; Georgia Insitute of Technology; University of Pennsylvania; University of Pennsylvania; Georgia Insitute of Technology email@example.com
Model locomotors (e.g. legged robots) have begun to achieve mobility comparable to organisms on hard ground but suffer significant performance loss on granular media (e.g. sand). Based on observations of lizards and crabs running on both hard ground and granular media, we hypothesize that organisms modify their gaits on granular media to take advantage of its solidification properties to achieve high performance. We test this hypothesis in laboratory experiments on a model locomotor, a six-legged 2.3 kg robot, SandBot, on a controlled trackway of granular media (poppy seeds) as a function of limb rotation frequency 4 < ω < 30 rad/sec and material preparation (packing fraction 0.58 < Φ < 0.63). A fluidized bed sets the initial Φ via repeated pulses of air through the granular media. Kinematic parameters which generate a bouncing alternating tripod gait yield average speeds (va) up to 50 cm/sec on hard ground but result in a slow swimming motion in granular media (~ 1 cm/sec). With proper adjustment of the limb kinematics, SandBot achieves va of up to 30 cm/sec on granular media using a pendulum-like walking gait. A model of Sandbot's motion based on balancing inertial and granular forces indicates that properly tuned kinematics minimize inertial stress and simultaneously maximize grain stress. Systematic variation of Φ and ω reveal that va of the robot is a sensitive function of both parameters. For fixed Φ > 0.6 and increasing ω , va displays a maximum at a frequency ω*(Φ), beyond which va decreases rapidly with increasing ω. For ω < ω*, the robot walks using a pendulum-like gait and for ω > ω* it swims using a paddling motion.