Oh, to have a half-million-dollar Vicon motion capture system. Look at what you can do with it (in the lab)!
From IEEE Spectrum:
"The University of Pennsylvania's GRASP Lab, famous for those crazy quadrotors that can fly through windows and hula hoops, has been working on getting groups of the robots to fly together in formation. Just like with a formation of fighter jets, there's a leader robot in each squad along with several follower robots. The followers have just two jobs: follow the leader, and preserve the shape of the formation.
Being able to do this is all about communication, as Professor Nathan Michaeldiscussed today at the IEEE International Conference on Robotics and Automation (ICRA) in Shanghai. As he and fellow researchers Matthew Turpin and Vijay Kumar have discovered, the robots have to not just know exactly where they are, but they also have to broadcast that information to their neighbors to maintain the integrity of the formation. This processing is all done on each individual quadrotor, so there's no all-seeing computer watching everything and telling each robot where to go. The accuracy is impressive: 50 percent of the time the quadrotors are within a mere two centimeters of where they should be.
So what happens when some robots can't talk to each other? If a robot fails for some reason, it's able to bow out from the formation gracefully, and the other robots can move on without it, preserving the shape of the formation. You can see an example of this in the above vid. It's an important capability: part of the advantage of having a group (or a swarm) is that it can be resilient to individual failures, but to harness this resiliency, you need to not have one failure cause a disruption to the rest of the group."