One Kilobot is not very smart. Each quarter-sized bot scuffles along on three rigid legs and can communicate only with its neighbors. Yet by instructing more than 1,000 Kilobots to follow a few simple rules, computer scientist Radhika Nagpal and her team at Harvard can get the crude bots to assemble into multiple shapes — including a wrench (left), a star and the letter K — without human intervention.
The demonstration, reported in the Aug. 15 Science, is the closest scientists have come to mimicking cooperative swarms in nature, such as ants that clump together to form makeshift rafts (SN Online: 6/17/14). Previous attempts involved smaller swarms of more expensive and sophisticated robots. But Kilobots, which the Harvard team developed in 2011, cost about $20 apiece; they move using the motors that make cellphones vibrate. The trick was developing a program that made the most of the bots’ capabilities, along with patience: The bots need about 12 hours to form each shape.
Eventually researchers hope to develop intelligent swarms of sand-grain-sized robots that autonomously form 3-D structures — say, an actual wrench.
To entice robots to form shapes, researchers upload an image of the desired shape (shaded area) to each bot. The four white bots are called seed robots — they mark the position and orientation of the shape and never move. The other bots use information from neighbors to figure out their distance from the starred seed bot; the farthest ones (darkest red) start moving along the edge of the swarm. Upon reaching the seed bots, the moving bots are able to triangulate their exact position. The bots stop when they are within the shaded area and either reach the boundary or touch the bot that has just stopped in front of them. Following these rules, the bots gradually fill in the shape.
Credit: M. Rubenstein et al/Science 2014, Adapted by S. Egts