Earlier this year, ETH Zurich demonstrated how quadrotors tied to a pole with string could cooperate with each other to do some fairly impressive acrobatics. It was a lot of fun to watch, but it wasn’t exactly clear where it was headed as far as any sort of practical application. I mean, quadrotors on leashes? What could you possibly do with that?
We’ve seen aerial robots constructing things with rigid elements before, but that’s hard, because your localization and control has to be dead-nuts accurate, and the weight of the stuff that you’re hauling around puts severe limitations on the endurance. So the researchers—the project is a collaboration between ETH Zurich’s Institute for Dynamic Systems and Control and architecture firm Gramazio Kohler Research—decided to try something different. Their idea of using rope (specifically, polyethylene fiber, which has a high strength-to-weight ratio) takes into account what quadrotors are good at, and for many applications (like lightweight bridges), tensile structures are as good as (or better than) rigid ones.
The bridge that the quadrotors wove spans a 7.4-meter gap using a total rope length of about 120 meters, and uses a variety of techniques that outdoorsy types are probably familiar with, including knots, links, and braiding. Each quadrotor carries a motorized spool that allows it to control the tension on the rope, and a plastic tube makes sure that the quadrotor doesn’t (fatally) entangle itself.
We have to point out every time we see stuff like this that there’s a very fast and expensive external localization system working very hard in the background to track each of the quadrotors and make sure that they go where they’re supposed to go and not run into each other. So, getting something like this to work over the river Kwai is going to take a bit more work, but I love the idea of (eventually) pulling a few flying robots out of a backpack and commanding them to make a bridge while I eat a sandwich and watch.
Meanwhile, in order to truly express their confidence in the structure that their robots have created, I think next time it would be appropriate for the researchers to make their way across the bridge with all of their quadrotors hovering angrily below them. We’ll be sure to bring this up next week when we get updates at IROS.
[ ETH IDSC ]
Evan Ackerman is a senior editor at IEEE Spectrum. Since 2007, he has written over 6,000 articles on robotics and technology. He has a degree in Martian geology and is excellent at playing bagpipes.