Mike,putting the IR stuff underneath would definitely reduce the range some, but it also makes it omni-directional as the light reflects off of the table top. I haven\'t actually tested this myself, but I have seen that design used on a few other robots (kilobots.) I\'d estimate that they would be able to detect each other at about 4-5 inches.
Eric, ty, I would like to add a charger to it. I\'m thinking a 2 cell lithium with the appropriate charger circuit, if I can figure it out :p
I will be building some of these for certain, I\'ll report back when they are presentable.