Leaping lizards help design robots with tails

A group of biologists and engineers have been inspired by lizards and dinosaurs to design robots with tails that will help them to remain upright when they stumble during leaps.

The team of researchers, including undergraduate and graduate students from the University of California, Berkeley, studied how lizards manage to leap successfully even when they slip and stumble.u00a0They found that swinging the tail upward is the key to preventing a forward pitch that could send them head-over-heels into a tree.

The scientists subsequently added a tail to a robotic car they named Tailbot and discovered that it's not as simple as throwing one's tail in the air.u00a0Robots and lizards have to adjust the angle of their tail just right to counteract the effect of the stumble. Given an actively controlled tail, even robots can make a leap and remain upright.

"We showed for the first time that lizards swing their tail up or down to counteract the rotation of their body, keeping them stable," Robert J. Full, the team leader, said.u00a0"Inspiration from lizard tails will likely lead to far more agile search-and-rescue robots, as well as ones having greater capability to more rapidly detect chemical, biological or nuclear hazards," he said.

According to Full, agile therapods like the velociraptor depicted in the movie 'Jurassic Park' may also have used their tails as stabilizers to prevent forward pitch.u00a0The new research tested a 40-year-old hypothesis that the two-legged theropods, the ancestors of birds, used their tails as stabilizers while running or dodging obstacles or predators.

For the new study, Full and his students used high-speed videography and motion capture to record how a red-headed African Agama lizard handled leaps from a platform with different degrees of traction, from slippery to easily gripped sandpaper.

They coaxed the lizards to run down a track, vault off an obstacle and land on a vertical surface with a shelter on top. When the friction on the obstacle was reduced, lizards slipped, potentially causing their body to spin out of control.

When they saw how the lizard used its tail to counteract the spin, they created a mathematical model as well as Tailbot to better understand the animal's skills.u00a0With a tail but no feedback from sensors about body position, Tailbot took a nose dive when driven off a ramp, which mimicked a lizard's take-off.

When body attitude was sensed and fed back to the tail motor, however, Tailbot was able to stabilize its body in midair. The actively controlled tail effectively redirected the angular momentum of the body into the swing of the tail, just as with leaping lizards, Full said.u00a0"Engineers quickly understood the value of a tail," Thomas Libby, a mechanical engineering graduate student, said.

"Robots are not nearly as agile as animals, so anything that can make a robot more stable is an advancement, which is why this work is so exciting," he added.u00a0The study has been recently published online in the journal Nature.

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