Micro-robots may soon be available for deployment by the thousands. Consequently, controlling and coordinating a force this large to accomplish a prescribed task is of great interest. This paper describes a flexible architecture for deploying thousands of autonomous robots simultaneously. The robots' behavior is based on a subsumption architecture in which individual behaviors are prioritized with respect to all others. The primary behavior explored in this paper is group formation behavior drawn from the work in social potential fields applications conducted by Reif and Wang, and Dudehoeffer and Jones. While many papers have examined the application of social potential fields in a simulation environment, this paper describes the implementation of this behavior in a collective of small robots.