[sciguy125]

It might be interesting to try to come up with a communication protocol using infrared. Depending on your budget (and willingness to abide by federal law), radio might not be within your reach.

If all the robots had IR transmitters and recievers, they could all talk to each other and also send out broadcast messages to everyone. It'd probably have to be designed something like ethernet though. Each robot gets an "address" and only looks at packets that are directed toward itself. I think the method of making sure that only one robot talks at a time might get funky though.