I stumbled across this thread and have a question. What is the typical fit of the motor bearings, which is, I think, what they call the "C" rating for how tight the components fit together and how free the bearings turn. In my work experience we had bearings that were all over the range in printing presses and bindery equipment that had to spin at high RPM and low speeds, high and low load factors. Some carried huge amounts of radial load. Lubrication ranged from factory applied grease to chilled oil that flowed through the bearings that were under heavy loads. Are the motor bearings typically factory sealed and lubricated? The one motor I have taken apart was on a club member's model that had seized in flight, and was making piercing screeching noises just before doing so. We swapped out the motor and I took the old one apart just to check it out, and found the motor full of debris. All sorts of junk from bug parts, to gravel, seeds (I think) and something had got between the armature and the magnets and broke one of those free. I gave the motor back to him to rob parts from it but don't remember what the bearings looked like, but I did check them to see if the spun freely and they did. I think all this junk gets sucked into the motors, especially when spooling up on the ground and while taking off, and can cause issues. They have to have cooling air. As far as arcing, I wonder if replacing the grease in the bearings with dielectric grease would offer any positive results if arcing does prove to be an issue. I wonder what kind of amperage we are talking about at that point when the motor is at full operating RPM ?
Type at you later,
Dan McEntee