Michael Rubenstein,  Alejandro Cornejo, Radhika Nagpal

Science 15 August 2014:  Vol. 345 no. 6198 pp. 795-799 

Self-assembly enables nature to build complex forms, from multicellular organisms to complex animal structures such as flocks of birds, through the interaction of vast numbers of limited and unreliable individuals. Creating this ability in engineered systems poses challenges in the design of both algorithms and physical systems that can operate at such scales. We report a system that demonstrates programmable self-assembly of complex two-dimensional shapes with a thousand-robot swarm. This was enabled by creating autonomous robots designed to operate in large groups and to cooperate through local interactions and by developing a collective algorithm for shape formation that is highly robust to the variability and error characteristic of large-scale decentralized systems. This work advances the aim of creating artificial swarms with the capabilities of natural ones.

Large-scale robotic self-assembly

When individuals swarm, they must somehow communicate to direct collective motion. Swarms of robots need to deal with outliers, such as robots that move more slowly than the rest. Rubensteinet al. created a large swarm of programmed robots that can form collaborations using only local information. The robots could communicate only with nearby members, within about three times their diameter. They were able to assemble into complex preprogrammed shapes. If the robots' formation hit snags when they bumped into one another or because of an outlier, additional algorithms guided them to rectify their collective movements.

Inspired by biological examples, like cells forming organs or ants building bridges, the work could help develop self-assembling tools and structures.

"Each robot is identical and we give them all the exact same program," explained Dr Michael Rubenstein, the first author of the study, which is published in Science.

"The only thing they have to go on, to make decisions, is what their neighbours are doing."

The robots are 3cm across and cylindrical - about the size of a sushi roll. Dr Rubenstein and his colleagues at Harvard University dubbed them "Kilobots" and built 1,024 of them altogether: the same as the number of bytes in a kilobyte.

Each Kilobot shuffles on three straight, spindly legs, chosen because they are cheaper than wheels. The robots' arena is a large wooden square, about the size of a tournament snooker table, complete with edges to stop them waddling off the edge.’