To run nimbly on sand, robots learn from nature

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Georgia Tech's SandBot is helping researchers understand how creatures like crabs can move across sandy terrain. Image: Daniel Goldman/Georgia Tech

Spiders and crabs can scurry rapidly on sand and dirt. Geckos and cockroaches can move nimbly over bark, leaves, and grass. How do these creatures do that? And can we copy them to design agile robots?

Daniel Goldman and his colleagues at Georgia Tech may have the answer. At the CRAB Lab (Complex Rheology and Biomechanics Laboratory), Goldman combines physics, biology, and robotics to investigate "rapid locomotion on sparse substrates with low foothold probability." Translation: they study how myriad creatures like lizards, cockroaches, and, yes, crabs, navigate challenging terrain, trying to understand the principles of locomotion.

The researchers report some of their results in a paper titled "Sensitive dependence of the motion of a legged robot on granular media," which appeared this week in the Proceedings of the National Academy of Sciences (PNAS). [Download the PDF here. See the press release here.]

In their experiments, they used a small robot with six legs that rotate independently. They call it the SandBot. They put the robot, designed by Haldun Komsuoglu and Daniel Koditschek at the University of Pennsylvania, on a bed of granular media (poppy seeds!). Tiny holes in the bottom of this bed trackway blow air, creating a loosely packed material whose density the researchers could adjust.

They made the robot traverse the track, testing different terrain densities and rotational speeds for the legs. One of the interesting findings is that if the legs move too fast, the robot just thrashes around -- what the researchers call "slow swimming." By carefully adjusting the rotational speed of the legs, however, the researchers were able to make the robot move fast, without skipping in place.

The Georgia Tech team says their work could help biologists studying animal locomotion and also roboticists trying to design better limbs for complex terrain. Their insight could prove useful in applications like space exploration and search-and-rescue missions. Or running on the beach.

PS: Goldman is preparing an in-depth article on this work for Spectrum's April issue.

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