Programmable self-assembly in a thousand-robot swarm

https://www.youtube.com/watch?v=xK54Bu9HFRw

Fish gotta school, birds gotta flock, and robots, it seems, gotta swarm. At least, that’s what they’re doing on the workbench of Harvard University computer scientists Michael Rubenstein and Radhika Nagpal and Massachusetts Institute of Technology computer scientist Alejandro Cornejo. Each of their 1024 robots, called Kilobots, is a three-legged disk the size of a U.S. quarter, sporting a single curl of metallic hair. En masse, they form a mechanical multitude an order of magnitude larger than any robot swarm ever built—a possible precursor to future robot work squads choreographed for chores such as cleaning up oil spills.

“That is a beautiful accomplishment,” says Hod Lipson, a roboticist at Cornell University who was not involved with the work. “Really getting a thousand robots to perform in sort of perfect synchrony.”

The idea for swarms of robots working together comes from nature. Army ants link themselves together to form rafts and bridges, and neurons in a brain fire off signals that collectively create intelligence. They do it all by following collective algorithms—shared sets of rules and instructions—and taking their cues from what’s going on around them. Each individual is “just doing its own thing, locally. But fantastic things emerge out of their collective behavior,” Lipson says.

In the past, a group of scientists including Nagpal created small teams of termitelike robots that built simple structures by similarly obeying a shared algorithm. But the robot termites were only a trio. Roboticists have long dreamed of making robotic collectives that could rival natural ones in number and function. Researchers had played around with thousands of virtual robots in computer simulations, but making that vision a reality was no simple task. “Truth is, things rarely behave the way we simulate them,” Nagpal says. What’s more, she adds, “making a thousand robots is really hard.”

The team solved the problem of getting all 1024 robots to communicate by putting an infrared light transmitter and receiver on each robot’s belly and programming them to pulse messages to one another. Their three little metal legs both vibrate, letting the bots scuttle along, and are a charging mechanism. Sitting atop one charging plate with another plate pressing down on the Kilobots’ single metallic hair, every bot can recharge its batteries at the same time. They kept the robots simple, Rubenstein says, because “every penny you spend on each robot becomes $10.00 for the whole swarm.”

The results, described in a paper published online today in Science, are “very simple agents that can self-organize, can collaborate” to create any 2D shape, such as a star or a wrench.When they want to start making a shape, one Kilobot flashes out a signal that passes through the swarm like a game of telephone. The signal robot tells the whole swarm where the original robot is, how to find it, and what shape to make, with it as the starting point. The other robots then figure out where they are by talking to the robots around them and begin filing into place. As in a colony of ants, “there’s no centralized leader per se,” Rubenstein says. “Every robot is just talking to its neighbors and making its own decisions based on what it sees in its environment.”

“This is the holy grail of what we want to do with robots,” says James McLurkin, a roboticist at Rice University in Houston, Texas, who was not involved in the project. He says the Kilobots give scientists a platform to test new ideas and programming on an actual, physical thousand-bot swarm instead of just unreliable simulations. Eventually, that might lead the way to developing real search-and-rescue robot teams or robotic construction crews. “This breakthrough points toward searching the whole ocean for downed aircraft. Dropping robots off in harm’s way, and they build you an airfield. You drop ’em all off in a cave, and they come back with a map,” McLurkin says.

“One interesting future direction is to allow the robots to attach to one another,” Rubenstein says. A bucket of linking robots could be programmed to stitch themselves together into larger Transformers-like tools as well as to roam about in massive teams, he says. Nagpal acknowledges that Kilobots won’t be tackling real-world tasks any time soon. Still, she hopes such applications are coming. “I’d love to build robots like that,” she says.