How to force an army of self-propelled mindless robots to act collectively?

We study assemblies of rodlike robots made motile through self-vibration. When confined in circular arenas, dilute assemblies of these rods act as a 2D gas of molecules. But above a critical surface fraction, some fraction of the bots line up in one or more tight clusters along the corral boundary while, in the bulk, gaslike behavior is retained. We find that the unified pushing of the cluster bots can drive collective motion: by selecting corrals that are deformable but free to move, we take advantage of surface cluster formation to force the robot army to work together.