Hi, My nephew has a toy rc helicopter. It has a main rotor motor and a tail rotor motor (both little dc motors). Their RPM is linked (if you speed up the main rotor, the tail rotor also speeds up, because it has to generate the necesarry counter-torque). Yesterday, the tail rotor motor broke down, so the helicopter only spins clockwise and is no longer flyable. I tested the wires to it, and they're still ok (about 9V at maximum throttle). So I guess the motor itself is broken. I have a dc motor of about the same size lying around, and I would like to replace it. The problem is that I don't know if the RPM will be the same as the original motor. If the RPM is too high, the helicopter will spin counterclockwise, if it's too low, it will spin clockwise. Can I just put a resistor between the motor and the supplying wire to create a volage drop to lower RPM? Or am I missing something here? PS: The original tailrotor motor has a little PCB with 2 tiny capacitors soldered to it. I think I will be able to desolder it and solder it to the replacement motor. (I guess the capacitors have something to do with clearing out minor peaks and disruptions in current).