Compressed air for rapidly cooling motors?

[Al Skierkiewicz]

OK,
So there is some common myths here that rear their head every few years or so.
The CIM motor heat is for the most part due to resistive losses in the armature and to a lesser extent, the friction caused in the shaft bearings and the brush assy. Teams who try to cool the exterior of the motor do not remove this heat and as Don has pointed out, shocking the ceramic magnets can lead to a shattering risk. Those parts of the magnet that will break off will lodge between the magnet and the armature. Also rapid heating/cooling will reduce the magnetic fields in the magnets. This will not be apparent for many teams but I have experienced it in motors that require a specific output power for the work they are doing. (video head motors and capstan motors on tape machines for instance)
Teams who use the cooling spray method generally have searched around for the best cooling ability. There are circuit cooler sprays that are available that do use fluorocarbons. While these do produce a lower temperature, the heat still internal to the motor is not removed. It is pretty easy to see that spraying with these products cause ice to form on the surface that will rapidly melt and produce condensate on the surfaces that have been treated. They simply cannot remove enough heat to be effective.
Yes teams also spray the main breaker, but in this case there simply is not enough thermal mass inside the main breaker for this method to be effective.
Additionally, the fluorocarbons used are also solvents. To spray them on devices that are not sealed will cause lubricants to be washed out. Luckily, the CIM shaft is closed on one end and normally behind a transmission case on the other so very little of the solvent enters that motor. There are also rubber seals on the two ends plates. It does however, work it's way into other motors like fans, and servos, and wheel bushings and bearings.
While we are on the subject of internal motor heating, many of you are using the 775 motor and others like it. Please note that there are vents at both ends of the motor as well as slots on the side. This motor has an internal fan that pushes air out the side slots. It must pull air through the slots in the end of the motor to cool the armature. If you mount this motor on a planetary gear box without using the slotted adapter plate, the armature of the motor will get hot as no air will be pulled in from the shaft end of the motor. Additionally, if you running this motor at a slow speed, the fan is not running at an efficient speed to move cooling air through the motor.