did just that (French, Google translation) with the help of an Arduino, a few modifications to the receiver, and an IR rangefinder.
The stock RC tank includes servos to move the turret and the requisite electronics to fire an Airsoft gun. The precision of the mechanical movements inside the turret weren’t very precise, though, so [Vincent] had to gear down the servos to turn large movements into slight adjustments. After that, he installed an IR rangefinder and laser diode onto the barrel that allowed the gun to sight a target and read its distance.
After some experimentation with the rangefinder and laser, [Vincent] plotted data from firing a few BBs at a whole bunch of distances and targets. The graph came out fairly linear, and after plugging this into a graphing calculator, he was able to find an equation that took into account the distance and angle so the Arduino-powered fire control computer would hit its mark.
The accuracy of the gun is very impressive, all things considered. [Vincent] is able to accurately fire BBs downrange and hit an 8×12 cm target at five meters. You can check out that action below."
[From Hack a Day at http://hackaday.com/2013/06/11/giving-an-rc-tank-a-fire-control-computer/#more-98859]
[Original article at http://www.bricobidules.com/index.php?category/Arduino/Charduino]