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Tail Spin

March 17, 2012
by Anne Pinckard
A lizard and a toy car

Robots learn a thing or two from lizards.

Just like cats, lizards can use their tails to right themselves so they land on their feet. Now this neat little trick is the basis of a new robot design, thanks to graduate student Thomas Libby ’02 and a team of Berkeley researchers. Called “Tailbot,” the device was hacked together from a radio-controlled car and common electronic parts—and sports a tail.

The team observed how lizards, leaping from a slippery block to a wall, used their tails to manipulate their body position and compensate for the lack of footing. The team then developed a simple program that would move the robotic car’s tail up or down in response to the position of the vehicle’s chassis, preventing it from taking a nose dive, falling on its back end, or spinning head over heels. The technique takes advantage of Newton’s Third Law, that for every action, there is an equal and opposite reaction. When the robot’s tail swings up, the reaction on the body moves the nose upward.

But the researchers added a twist. A lizard’s tail is tapered at the tip, with the majority of the mass at the base. Libby’s team realized they could make the tail more efficient by weighting its end. The improvement exemplifies the difference between bio-inspired designs and biomimicry. “You don’t want to say ‘This is what the animal is doing, so we’re just going to do it that way,'” Libby explained. “You want to understand why the animal is doing it that way and what selective advantages it has for the animal, and then take the good parts.” This is the underpinning philosophy behind the Center for Interdisciplinary Biological Inspiration in Education and Research, a six-year-old program of which Libby is technical director. At CIBER, the lizard research was conducted in part by graduate and undergraduate students in the program, who coauthored the study published in Nature.

The tail works well for a small radio-controlled toy, and Libby envisions it could one day help search-and-rescue robots maneuver rubble. As the vehicle gets bigger, however, he expects the dynamics to change. The details are the subject of an upcoming paper, due out in summer. For now, Libby speculates that at some point the tail will get so big it can’t move into position soon enough to effectively reposition the chassis.

“So a monster truck with a tail would probably be a little extreme,” he said. “Not to mention you probably won’t want to be standing next to it while its tail controller is activated.”

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