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.
STAYING UP A flapping-wing machine ascends and hovers in stable flight without sensors or feedback controls. A closeup shows how a tiny motor drives the flapping mechanism, which resembles a jellyfish’s bell expelling water.
Credit: L. Ristroph and S. Childress/J. Roy. Soc. Interface 2014, adapted by Ashley Yeager