Waterproofing of brushless motors

As you have probably already tested, a normal model airplane brushless motor is perfectly capable of operating underwater.
However, when tested in simulated corrosive seawater, it becomes clear that such brushless motors with untreated exposed coils are quite unreliable.

There are three types of problem

Corrosion and rusting
2. Electrical shorts
3. Wear and tear inside the motor due to underwater particles
So we need to do something with the brushless motor in order to achieve a low cost solution for underwater propulsion.

Electrical shorts are the easiest to avoid. The motor's enamelled wire does not cause a short circuit if it is not damaged, the only exposed uninsulated areas are the three solder joints of the motor.

It is usually very reliable to prevent short circuits by applying resin and waiting for it to cure.



For motors without pads they are wrapped directly in heat-shrink tubing, which can of course be heated and sealed by applying hot-melt glue first and then applying heat-shrink tubing.
Corrosion is the least easy to deal with.
The motor housing will generally have electroplating treatment is less prone to corrosion, but also with stainless steel materials and after anodic oxidation of the shell, do not worry too much. Of course, if you use titanium alloy as the shell material belongs to how will not corrode.
Corrosion can seriously affect the performance of the motor, the ball bearing corrosion is very fast, will produce noise and vibration. Corrosion at the bearing mounting can also make it difficult to remove for maintenance. Stainless steel bearings, or ceramic bearings, can be tried. Ceramic bearings can be self-lubricating and the ceramic does not corrode. They are generally stainless steel ceramic hybrid bearings, which have a stainless steel cage. There are also high performance plastic bearings, generally plastic bearings may have problems at high speeds. Of course if you have the machining capability you can use a copper bushing like the one below, which can be relatively noisy in the air.



Corrosion can also occur in motor cores. The inner rings of the silicon steel sheets are complete with electrostatically sprayed insulation resin, the outer rings are not sprayed in order to ensure that the air gap is small enough (around 0.2) to require dimensional accuracy. The outer ring must be treated. Bearings and shafts as well as cores can be lubricated to lubricate and also to isolate water to prevent corrosion. Regular care is required.



The coil section, once the paint has been damaged the motor is almost obsolete. Serious care is needed to protect it.
There are also many methods.
The cruder ones are direct application of resin or other glues and spray paint (the white coating in the picture)




Effect of transparent resin.