[EricH]

If it fits within the cost limits, is powered either by the robot's 12V supply via PDB (custom voltage-reduction circuits, as I recall, are legal within reason, but check the rules on that) or by an integral battery, does not directly control motors/pneumatics, and does not violate any other rules, it is allowed.

At least, under the 2014 rules. Given that there will be a new control system in 2015, I wouldn't be surprised to see some sort of change.