Swarm Robots - I Love the Idea

For a long while now I've wanted to create my own little flock of swarm robots. In Prey, Michael Crichton shows us what swarms of nanobots can do and that's a great book to read for inspiration. However, since nanotech is not within reach of most of us, I wonder about microtech level robots. Driving home from UWaterloo the other day I was pondering how one might create a Really Simple Swarm Robot - a mechanical flocking device that is super cheap and super simple. In my mind I saw a steam punk version of a swarm robot that could move, get inputs from nearby other bots or the environment, and communicate that to the others.

I confess that I have recently watched Hugo and the movie provided fresh inspiration for the development of some sort of swarm bot based on mechanical rather than electrical means. This swarm robot website was pointed out to my by my Network Science 675 professor and is really interesting as well. One approach they use is to enable the robots to read light as a kind of pheromone for emergent property formation. I like it.

Could you use hollow styrofoam balls that somehow interact with each other in a directional way? Would magnetism be a useful information or energy transfer medium? It can be complicated to work with but perhaps the movement could be constrained in two dimensions somehow or along a track with the emergent behaviour falling along a single distance-between vector.

If anyone has seen something like this, I'd love to learn more about steam punk robotics.