Hummingbirds do it, bees do it. But for tiny robots, hovering has proven a challenge.
Flapping-wing robots known as ornithopters can replicate insect wing motions, but these designs require complicated mechanisms to keep the machines stable. So mathematicians Leif Ristroph and Stephen Childress of New York University departed from insect mimicry. The pair designed a 2.1-gram, 10-centimeter-wide hovering machine that rises in air like a jellyfish in water.
Four teardrop-shaped flapping Mylar wings attached to a spherical shell create lift. A small motor drives a crankshaft attached by rods to each wing. Wings opposite each other flap simultaneously; the pairs are out of phase by a quarter cycle. The result, reported January 15 in the Journal of the Royal Society Interface, is the first flapping-wing craft with intrinsic stability, meaning it keeps itself right-side-up without sensors or feedback controls.
The machine looks innocuous enough — even cute. But potential applications of automated hovering robots are serious stuff, with surveillance, environmental monitoring and search-and-rescue topping the list.
A jellyfish – the inspiration for a tiny flying robot built by a team from New York University. While unconventional in its design, the jellyfish-bot could pave the way for the next generation of intelligence and environmental data gathering drones.
The jellyfish-bot, built by a team led by Leif Ristroph, an associate professor of mathematics at NYU, weighs just 2 grams, and has a wingspan of just 8 centimeters. At the moment, the robot connects to a tethered power supply, and has no steering mechanism. But Ristroph tells News Scientist that improvements in the design could allow the tiny bot to carry a battery, freeing it to fly anywhere.
Most flying robots – commonly called drones, or unmanned aerial vehicles (UAVs) – are made to resemble helicopters, airplanes, flying insects, or birds. These aircrafts, however, must constantly fight with the wind, and make adjustments to stay on course. According to Ristroph, his drone is made for the exact opposite purpose – to be picked up by the wind and carried away. In doing so, the jellyfish-bot is perfect for monitoring things like air quality, says Ristroph. Of course the military could also make use of such a drone – though Ristroph tells NBC News that he envisions it being used for some type of “nice peace-time application,” like environmental quality checks.
For now, the jellyfish-bot remains in prototype form, which can be seen below in this fascinating video that looks like it was shot sometime around 1910. (It wasn’t – it just looks that way thanks to the oddly antiquated production value.)
Tiny flying robots usually mimic nature's flyers, like birds and insects – but perhaps that's due to a lack of imagination. A four-winged design created by Leif Ristroph and colleagues at New York University, which boasts a body plan reminiscent of a jellyfish, is more stable in the air than insect-like machines.
The prototype consists of a carbon-fibre frame surrounded by two pairs of thin plastic wings that open and close when driven by a motor. Its shape allows it to fly upright with little effort, without requiring sensors or intelligence to adjust its wings like those used by insects. "Making a dumb machine is a nice strategy for very small robots," says Ristroph. "Without circuits and sensors, it's also lighter."
The robot is tethered to a power source for now, but improvements to the motor and wings should soon let it roam free. "If you could fine-tune the shape and flexibility of the wing, you could generate more lift, which could hold a battery up," says Ristroph.
The design should be especially useful for making centimetre-scale robots that drift through the air. It is quite robust – it can crash into objects while remaining unharmed – and with a weight of 2 grams it easily gets carried by a breeze, which could be an advantage. "We could use this type of robot to float around and take measurements, for example to monitor carbon dioxide concentrations in the atmosphere," says Ristroph.
The robot has often been compared to a jellyfish due to its similar overall shape. While it wasn't designed with that animal in mind, Ristroph says it could easily be modified to move underwater. "In the water, you don't have to worry about lift," he says. "The challenge was to make something fly: compared with swimming it's much more difficult."
Watch the robot hover and climb in the air
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