Aug 06 2015
A researcher at New York University’s Courant Institute has developed a small flying robotic device that takes its motion from that which a jellyfish does to move itself through water.
Leif Ristroph, assistant professor of mathematics at Courant Institute at New York University, says the device was developed as part of his Applied Mathematics Laboratory’s continuing work on understanding unsteady aerodynamics and fluid structure interactions.
“We didn’t officially name our robot, though we call it a ‘flying jellyfish,’ ” Ristroph says. “Maybe ‘aerojelly’ would be a nice name.”
Ristroph says the flyer is an ornithopter, or flapping wing aircraft, about 4 inches in size, that fits in a person’s hand.
“The concept is to have a membrane or set of wings that close and open somewhat like a jellyfish closes and opens its bell,” he points out. “Our specific realization has four wings hinged from above and driven by a motor to collapse inward and then outward, squeezing air downward to generate an upward lift. It flaps these wings about 20 times each second in flight, so it appears as a blur to the eye.”
While the flying robot resembles a jellyfish’s action through water, its inspiration didn’t come from jellyfish but rather a set of experiments Ristroph and his researchers previously had done.
“These involved pyramid shapes that can hover when placed upright in a vertically oscillating airflow,” Ristroph says. “These earlier experiments involved an externally driven flow, provided by a loudspeaker. The idea behind our flyer was to have the relative motion between the wings and air driven by an on-board motor so that it can fly in open air.”
Thus far with the current version of the flying jellyfish, the researchers have not managed to get a battery on board. Its power is wired in through tiny copper wires connected to a direct current power supply, which allows the flyer to flit about in a one meter cubic volume, enough to study its flight dynamics and stability but not good enough for practical applications yet.
Ristroph notes the first prototype of the flying jellyfish is very simple.
“It does not carry anything other than the mechanical components needed for flight, like wings, transmission system, motor, and body frame,” he says. “One very nice thing we found is that the flyer does not need any sensors to keep upright during flight — it has so-called passive upright stability, which is a great convenience when we think about further miniaturization of such a design. No special stabilizing tails or other surfaces are needed, and no sensors and computers are needed either.”
Ristroph says he has received questions and comments from individuals associated with the U.S. Air Force but no officially-expressed military interest yet.
“We aren’t working with anyone right now, though we are filing a patent through New York University, which is interested in developing the flyer further,” he says. “There are some engineering hurdles — especially getting a battery on board — that we as physicists and mathematicians will have to rely on others to overcome.”
Ristroph hopes that the help of engineers will take his tethered prototype to the level of a free-flying, self-powered machine. In addition, he believes more study on what makes the flyer so self-stable is another interesting point to figure out.
“This is especially interesting, since we now know that the way insects fly is not passively stable, bur rather they rely on sensors and feedback control to keep upright,” he notes. It’s an exciting time for individuals involved in trying to build small-scale flying machines, especially unorthodox versions like those with flapping wings. Any one of their ideas might just be a significant advance.”
About the author: Alan M. Petrillo is a Tucson, Ariz., journalist who writes for national and regional magazines and newspapers. He’s the author of several books on historical military firearms; and two historical mysteries, Full Moon, and his latest novel, Asylum Lane, all available at www.amazon.com.
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