To be precise, Dr Rubenstein’s ’bot swarm (above) has 1,024 members (210 being a conveniently binary number), known apparently without irony as kilobots. Each is a rigid-legged tripod that moves around by vibrating. Kilobots communicate with infra-red light, which can reflect off the table Dr Rubenstein uses for his experiments, and are programmed with three types of behaviour.
One is edge-following, which allows a ’bot move along the edge of a cluster. The second is gradient-formation, which lets it know how many other ’bots a signal has been relayed through, and thus gives it information about the location of these ’bots and the shape of the cluster it is in. The third is localisation, which means it can agree a system of co-ordinates with its neighbours, so that they can measure distances between themselves.