'Sand pit' probes walking strategies
By puffing air upwards through a box of sand, a US laboratory has tested how lizards, crabs and robots cope with ground that is more or less "fluid".
They say the contraption is like a wind tunnel for studying movement on unstable surfaces.
Tests of this kind could help design robots to handle inconsistent terrain - such as might be found on Mars.
For now, the team has identified key aspects of leg shape and movement that help maintain speed on flowing ground.
The results appear in the journal Bioinspiration and Biomechanics.
"The pioneers of flight looked at different wing designs in a wind tunnel, and now we can do this with robotic design," said senior author Daniel Goldman, from the Georgia Institute of Technology.
By adjusting the rate at which air is pumped through the sand, Prof Goldman and his team can control precisely how fluid the surface becomes.
They used this system to observe the motion of a six-legged "Sandbot", four species of small lizard and one crab, over a range of conditions.
Then they modelled how the interplay of factors such as step rate, leg length and foot pressure affected the critters' progress.
Sure enough, it was shapes and gaits that minimise foot pressure that were the most useful on weak ground.
"It's important to understand the biomechanics and controls of good movement," Prof Goldman said. "If we can find out how these animals solve the problem, we can make better robots."