neithermovingnorstill wrote:Re Viscosity of Glycerin at cold temps:
I ran an experiment by putting some in my freezer overnight.
It does become more viscous, but not in the same way that sugar syrup does. If I tip the container, it moves slowly, but when I stir it, it's very easy to stir, very little resistance, so it is still effectively a fluid. Which is what you'd expect from something they put in antifreeze, because that wouldn't work if it became considerably more sticky at cold temperatures. It's a strange fluid, I'm confident it will work.
If you are confident that there is no glue used in the stator, you can probably use almost any solvent, as long as you remove the stator from the rest of the motor housing, and disconnect or cover any wires (the plastic shouldn't be soaked in solvent).
I like using orange oil for smaller jobs, but you'll likely need to soak your whole stator, so something cheap like gasoline should work fine.
If you think there is glue, and don't want to use solvent, I'd use a hair dryer rather than compressed air. Compressed air is very cold, but the hair dryer will make the ATF more runny. If it doesn't produce enough air pressure to push the ATF out, you could alternate with the hair dryer and a vacuum cleaner. Use gloves, the copper will be very hot.
That might be true, but even if the ATF doesn't dry, the motor running could heat it up and splatter it all over the stator, and since there isn't enough ATF to conduct the heat to the casing, and ATF isn't as conductive as Copper (almost nothing is), that might lead to some extra heat? There could be other stuff in there though, if it's a geared motor, fiberglass/resin powder from the composite gears, metal powder, dissolved plastic, etc. Probably a good idea to strip it by soaking it in solvent just to rule that out, because it's an easy fix if that's the problem.
Any solvent you want to soak it in should first be tested not to disolve the epoxy used on the stator.
The idea is to get as much fluid splashing over hot windings as possible, which transfers heat into the fluid by direct conduction, then the fluid falls/drips/runs back to the bottom of the spinning rotor magnet ring and transfers that heat the fluid absorbed into the side plates and magnet ring, which has a good thermal path to the outside air passing over it.
The thinner the fluid, the better the cooling performance will be. ATF is nearly water thin, which means rapid flow across the surfaces it's sprayed across, more heat transfer cycles between copper to case made, and better heat exchange.
Something that would be very interesting to do is to machine up and install a lexan side plate with a bearing cup in it, just needs to be strong enough to support the weight of the free spinning rotor. Then set the motor in a wheel stand with oil in it, give it a spin, and observe what the oil does while the motor is spinning. My guess is that if you fill the motor up to the point it's nearly to the axle, when you spin the motor, the oil slings in a ring around the stator, submerging the copper all the way around the perimeter. But... It might just sit in the lower half and only splash/dribble oil on the top side, I really don't know.