Wired has more:
Here’s how it works: A single “leader” bot knows the score and the positions other robots must be in to play the right notes at the right time. The leader sends this information to the robots closest to it, directing them to the appropriate positions on the virtual keyboard. Those robots, in turn, relay the information to the bots closest to them, mimicking the swarming behavior of insects.
The researchers hope to make the robots as efficient as possible by minimizing the distance traveled by each bot and using the fewest robots possible at any given time. This means the slower the tempo of the song, the fewer robots playing, and vice versa.