How Kilobots Work

Kilobots in Action
The Kilobot on the left is transmitting a signal by bouncing it off the table to the Kilobot on the right, which receives it.
The Kilobot on the left is transmitting a signal by bouncing it off the table to the Kilobot on the right, which receives it.
Image courtesy Michael Rubenstein, Nicholas Hoff and Radhika Nagpal

We said it before. We'll say it again: Kilobots are designed to be the ultimate algorithm testers.

Let's say emergency personnel want to bring robots onto the scene for a search-and-rescue mission. They'd need to know how well the machines could communicate with each other. This is where Kilobots are especially useful as test dummies.

Each robot can bounce an infrared signal off the ground to another bot beside it, allowing it to sense where it is in relation to others in the swarm (see picture). Bouncing that signal can also ensure that one's robotic neighbors are on the same page for when and how a task is supposed to be carried out . Knowing where other robots are is essential when it comes to locating objects in a given environment and bringing them back to the home base.

So far, there are three basic swarm behaviors Kilobots have mastered: foraging, formation control and synchronization.

Foraging is what it sounds like: commanding several robots to disperse and explore the area around them. With Kilobots, the idea is to chip away the time it takes to forage in a particular location. Here's where signaling to others in the swarm comes in handy. Michael Rubenstein, a researcher who helped design the robots, says foraging as a group is far more efficient than individually, especially in urgent situations.

"If there's a collapsed building from an earthquake, and there's a person who's stuck in that building -- if you send a single robot it might take a lot longer to find that person than if you send a large group of robots to find that person," he says. Although a collapsed building and a flat, white board are totally different environments, the algorithms used to navigate both are similar.

Another important part of effective swarms is formation control, the ability to behave in unison or in a specific part of the swarm. By maintaining communication with each other, Kilobots possess a virtual bearing sensor that gives each one a realistic sense of its position in the group. Instead of using hardware to achieve this, Kilobots make do with basic software and more advanced algorithms. Performing complex behaviors with as little hardware as possible encompasses the spirit of Kilobots.

In a system where every robot is expected to be on the same page, synchronization matters. If part of the swarm needs to perform a task for a certain amount of time and then switch to another seconds later, the entire group must have the same internal clock. One way to visualize this is to imagine a swarm of 1,000 Kilobots, with each using its LED light to represent a pixel in a larger video that can be viewed from above. To know which color to signal at any given time, every Kilobot must be using the same clock.

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