A Sky Full of Jellyfish Drones Seems Like a Pretty Good Nightmare
NYU mathematicians achieve a first: a self-correcting ornithopter.
Why, you ask, does the world need a flying jellyfish drone? In the immediate, its creators, a pair of applied mathematicians at New York University, suggest that the tiny self-stabilizing flying machine unveiled in a new paper might make for a good toy. But that’s not really it: the UAV solves a very vexing problem in new-school aeronautical engineering: how to make something fly like a bug or bird (viz with flapping wings, an ornithopter) that can maintain airborne stability without constant sensing and correction.
The ultimate problem is that flapping is an inherently unstable way to fly. Bugs and birds have gotten around the problem—they're making do—but human UAV engineers are mostly still stuck programming feedback-based flight control systems. According to co-designer Leif Ristroph, other research teams have created a couple of different prototypes so far that don’t need constant correction, but the trade-off is considerable, usually a giant floppy tail to act as motion damper to keep their bodies from rotating while sacrificing maneuverability.
Meanwhile, the NYU flying jellyfish drone is inherently stable. Hit the thing with a burst of wind and it will bob back upright.
Interestingly, the NYU teams don't quite understand the mechanism behind the self-correction. It seems to have something to do with drag and a very low center of gravity. If you try and push it over, the jellyfish flyer's formerly downward jet of air instead pushes it sideways, with drag slowing the lateral motion and the low center of gravity pulling it back upright. Once righted, the drone resumes bobbing more or less in place.
The prototype is only about 10 cm across and made of carbon-fiber loops and Mylar. So far, it needs to be tethered to a power source and can’t steer. The design itself came less from seagoing blobs than simple observations of differently shaped paper objects subjected to a vertical, oscillating current of air in a wind tunnel. The winners were pyramids and cones, which you can see well enough in the finished product.
Though, it’s hardly finished really. The design isn’t bad for mathematicians, but Ristroph told Physics World that he’s looking forward to what “real engineers” and hobbyists can do with the basic idea. Now, just imagine this drone surprising you in some dark woods, perhaps with a swarm of its friends.