[Sparks333]

Just a thought:
It seems to me that if one were to connect to the Digital I/O, you wouldn't want to choose the interrupt lines, whichever ports they may be. You wouldn't want to hook the +5v lines together, because of potential differences. How about powering both robots off a single battery, or hooking the batteries together? Both would be at the same voltage level, then. On the digital i/o only using ground and signal, it seems, may be a safe experiment.
This is outta my leauge, so I look forward to a response.

Sparks