Ph.D. student Li Wang figured out that the top hat must be as tall as five times the diameter from one rotor to another by flying drones atop one another. The 0.6-meter vertical space ensures the quadcopters avoid undercutting each other. A set of algorithms gives the drones the ability to quickly maneuver out of the way when they detect another robot next to or above them.

As drone swarms become more ubiquitous, they'll need systems like these to keep people and themselves safe. "It's not possible for one person to control dozens or hundreds of robots at a time. That's why we need machines to figure it out themselves," said Magnus Egerstedt, director of Georgia Tech's Institute for Robotics and Intelligent Machines.

Another team at the lab are finding ways for autonomous blimps to detect and react to human faces and hand gestures in a project to find better ways to get people interacting with drones. Slow-moving blimps are more approachable, according to the researchers, and may someday take the place of store greeters or information kiosks. "Imagine a blimp greeting you at the front of the hardware store, ready to offer assistance," said project lead Fumin Zhang. "People are good at reading people's faces and sensing if they need help or not. Robots could do the same. And if you needed help, the blimp could ask, then lead you to the correct aisle, flying above the crowds and out of the way."