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Winged robots may shed light on fly aerobatics

Researchers make flapping machines that take off

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3:36pm, May 2, 2013
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Robots that can flap their wings, hover and dart around like a fly could help scientists better understand the finer points of insect aviation, researchers report in the May 3 Science.

Flies can easily dart out of a flyswatter’s path or land on a surface blowing in the wind. Some research suggests that subtle changes in wing motion can create enough twisting motion for them to make sharp turns. Emulating fly aviation in the lab with robots could help scientists understand the details of insect flight. But doing that has proved difficult.

“People have been trying to build flapping devices like this for years.” says Michael Dickinson, a bioengineer at the University of Washington in Seattle, who wasn’t involved in the work.

At small scales, drag and friction gain importance in flight dynamics. As a result, many components in large robots, such as gears and pulleys, don’t work in tiny flying machines.

Robert Wood of Harvard University and colleagues had to improvise components to develop bodies, wings and muscles for their flying minibots. For the muscles, they used ceramic materials that display piezoelectric properties — meaning the materials can contract in response to an electric field. The researchers attached two flight muscles to a carbon-fiber skeleton and linked each muscle with a wing via plastic hinges at the skeleton’s top. Each of the resulting devices is about as big as a penny.

An oscillating electric field contracts the piezoelectric muscles, causing the wings to flap. Changing the field’s strength or frequency produces different flapping intensity or rate. The researchers programmed a computer to interpret information from real-time videos of the robot and tell the wings when to flap and rotate.

It took Wood and his colleagues a decade to get a robot to fly (SN: 12/15/12, p. 22). One night last summer at 3 a.m., Wood says, one of his students emailed him what he describes as “a really cool video” of a robot taking off, hovering and briefly flying. Since then, the researchers have gone through numerous prototypes, making improvements and conducting tests.

The best robots’ wings can flap 120 times a second, almost as often as real flies’ wings do. The robots use roughly as much power — about 19 milliwatts — as insects similar in size. The machines can hover, move back and forth between points and stay airborne for more than 20 seconds before crashing, the researchers say.

Wood notes a key limitation: The robots don’t have on-board power, sensors or controls, so they always have to be plugged in. Dickinson also notes that the wings’ flapping motion isn’t as sophisticated as that of real flies. Wood’s team and other researchers are working to address each of these concerns.

“It's a very impressive step forward,” Dickinson says. “But it also indicates how far engineers will have to go before they have a truly autonomous fly robot.”

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