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From New Scientist:
IT'S not just humans who find it difficult to run on sand, even the most nimble robots struggle when faced with a stretch of the white stuff.
Planetary rovers and earthbound rescue robots often need to travel across varying terrain, including sand and rubble. So Daniel Goldman, a biophysicist at the Georgia Institute of Technology in Atlanta, investigated what makes these surfaces such a challenge. His team studied a robot called Sandbot - which has six C-shaped legs and scampers across hard ground with the agility of a cockroach - as it waded through a bath full of poppy seeds. The density of the seeds was controlled by blowing air through the bath.
They found that if Sandbot's limbs moved too fast, or if the researchers loosened the packing between the grains even slightly, the robot would quickly switch from a walking motion to an ineffectual swim as it sank deep into the material. "What was surprising was that it only needed a small change of about half a per cent in either the limb-movement frequency or the packing of the grains to prevent the robot from walking properly," says Goldman.
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