That's a good point. Currently the ultrasonic sensor only detects distance rather than type, a tank could be killed by friendly fire.
IR pulses are unique and could be rejected, if the tank detected a "friendly" IR shot.
For example HuanQi pulses are different from Forces of Valor pulses which are different from Battle Machine pulses.
Currently my "hacked" tanks output all the pulses and accept all the pulses as hits.
I was thinking that I might add RF receiver to the tower to turn them "off" when I wanted to pass.
Alternately I could add an IR receiver to them and use an IR remote to turn them on/off. This is probably the cheapest method.
What do you think?