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Study of spider crickets a leap into aerodynamics

Rajat Mittal has had crickets in his basement for years, and he always tried his best to get rid of the six-legged pests. But one day he gave them a closer look.

He marveled at how far they could jump — about 60 times the length of their bodies. He saw that they touched down smoothly nearly every time, whatever the contours of the landing surface. He wondered how they could perform this feat so well and with such apparent ease.

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Mittal, a mechanical engineering professor at the Johns Hopkins University, has spent the past nine months leading a team of undergraduate researchers trying to find out — and pondering how future scientists might make use of their findings.

In a project some on campus call "Tiny Dancers," he and about a dozen students at the Whiting School of Engineering have been using high-speed cameras to capture and illustrate the hundreds of stages spider crickets pass through as they soar.

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The images have allowed the team to measure the movements of the insects' limbs at each stage and develop mathematical models of the drag forces acting on their bodies.

The data they're collecting, Mittal said, could illustrate the dynamic principles by which engineers could one day create microscale robots to traverse highly irregular surfaces — navigating the rubble after an earthquake, for example, or the surface of a newly discovered planet.

Spider crickets — members of the Orthoptera order that originated in Asia — are good models in that they jump between earthbound and airborne states.

"Let's say you're trying to search for people after a natural disaster, and that terrain is very complex, full of nooks, holes and crannies," he says. "A crawling robot could only do so much. If you had a flying robot, it would also have limitations. But if a microrobot could fly, land on any surface, and take off again, as these crickets do, it would be extremely helpful."

The project aims not to explore such potential applications but rather but to investigate the dynamics that could underlie them, Mittal said.

Unlike many schools of engineering, the department at Johns Hopkins routinely invites undergraduates to help lead research projects, usually ones that begin with a professor's interests.

Professors put out word they're seeking researchers, screen applicants and oversee the undergraduates as they design and carry out experiments.

Such projects can last two or three years, Mittal said, passing from one class or group to the next as they unfold, the researchers sometimes receiving stipends or course credit. If the results are promising, doctoral or postgraduate students often take over the work, applying for grants to expand the project into lengthier controlled studies.

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When Emily Palmer, a sophomore mechanical engineering major, heard of Mittal's interest in crickets, she suppressed her innate dislike of bugs — "I was so freaked out at first," she said — to pursue what she called a "rare opportunity" to work in an area of fluid dynamics she'd never encountered. (The field includes the study of air flow).

As Mittal's lead researcher, Palmer, a New Hampshire native, had to handle the dozen or so crickets he brought in from his basement, a collection that has bred its way to a population of about 30.

She was soon more fascinated than repelled.

"You see pretty much the same patterns in every single jump," Palmer said. "I can tell you what they'll do when they take off, when they'll do it and what they'll do when they land. That tells me there's an evolutionary reason that they jump the way they do. That feels very powerful to me."

She began working on the project on a volunteer basis, between classes, eventually joining forces with Nico Deshler, a high school senior from the Washington (D.C.) International School, who had heard about project and asked to participate.

Helping lead a small, evolving cast of undergraduates, they used three cameras with shutter speeds of up to 600 frames per second to record the insects' leaps. This allowed them to capture everything from the bugs' jump-friendly anatomy (they have hind legs "like drumsticks," Mittal said) to the distances they cover (the human equivalent of their leaps would be the length of a football field) and the ways in which they manipulate their six legs and two antennae at hundreds of points along their trajectories.

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Mittal, who has conducted research with the U.S. military, said the way they extend their appendages reminded him of how parachutists reach out with their arms and legs in free fall.

Insect and human alike, he said, appeared to use similar movements to "establish a stable posture," an effort that helps reduce tumbling, rotating or otherwise shifting position during flight, creating the conditions for an effective landing.

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Entering hundreds of measurements into a computer, the researchers developed mathematical models to quantify the movements — and showed in the process that the bugs do, in fact, establish a consistent degree of wind drag.

"We've shown that our hypothesis — that they're creating a stable posture — is correct," Palmer said.

She has presented the group's findings twice, once at a conference for young professionals at the Johns Hopkins University's Applied Physics Laboratory and once at the 68th annual meeting of the American Physical Society's Division of Fluid Dynamics in Boston last month.

Mittal said he'll work with undergraduates on the project until at least mid-2016, and it could last for three or four years if it generates enough interest. Future researchers, he added, could take up questions such as whether the flights work differently in the dark, what kind of trail the jumps leave and what biomechanics are used during takeoff and landing.

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In a broader sense, he said, "Tiny Dancers" only adds to a growing sense in the engineering field that when it comes to imagining devices that could help humans in the future, it pays to look to at the splendidly efficient creations nature has evolved — including the bugs in and around your basement.

"You see crickets and you think, 'Oh, man, these things are icky; let's squash them,'" Mittal said. "But slow things down and examine them for what they really are, and you see that they work in an incredibly beautiful way."

jonathan.pitts@baltsun.com


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