ORIGINAL: spektrumFlux
did not notice any resistence and I'm using a 2S 40~80C Lipo battery.
very puzzled why the wire could burn.
Turn the coupling with your finger, it should be smooth with no resistance for a full turn. There are several things that can hang up - the loading ramp fit (if you removed the jet drive), the shaft could have come forward when you attached the coupling, allowing the shaft to come out of the rear bushing, a piece of plastic caused by the injection moulding process that wasn't fully removed, etc. One other thing is too small or inadequate connectors can cause high heat. And it could have been a bad motor - it happens now and then. Do you have any pics - they might explain more.