Waterproofing a DC motor

I believe the best thing is to position motor out of the water or if you need to for some application try to in-case entire motor in a tube of some sort and seal that around the motor.may need to extend shaft and make a pump seal out of leather or rubber drill 1mm hole and small spring to push against bulk head should hold up pretty well as the leather will swell when wet look up pump seals on google to see how there designed may help

when i was a lad a long time ago tho we ran them under water with Little damage until rust set in when we were to lazy to blow out the water and spray with WD-40 brushless motors that is

try this site on google http://www.microrccenter.com/forum/index.php?showtopic=17824

If you can reach the windings enough as is or by disassembly, it is possible to seal the wiring of a small dc motor with epoxy to prevent shorts in the water. Just be very careful not to epoxy the motor solid. You will lose some efficiency with water running between the windings and magnets, but you'll avoid making a housing with rotating seals.

The easier way would be to use a shaft coupling and jump to a larger diameter shaft that you CAN buy a seal for.

What depth does this need to go to? If you are near the surface, I would suggest keeping the motor dry and using an RC stuffing box to get the motion to the water. The link the other guy had has good suggestions.

If you have to go VERY deep, or want to get over complicated, you can put the motor in a housing filled with non conductive oil (like baby oil). Connect a flexible bladder to that is exposed to the water to the housing, and you have a Pressure Balanced Oil Filled motor housing. That is the standard method for using electric motors and some other electronics in very deep sea applications. The bladder compresses and keeps the internal pressure equal to the outside pressure, so you never have a pressure differential between the oil in the housing and the water outside, so it is easy to keep sealed. Plus it's neat and fun to build.

Forgot to log in, that last post was me, in case anyone cares :)

Thanks. Yes we all do care!!

Not all of us, though.

If the motor is that small, then it's probably a low-torque application. How about putting a disk with two or more magnets on the end of the shaft? Then seal the entire motor/disk assembly (no sliding seals), and place another shaft with similar magnets in line with the original. In other words, use a magnetic coupling.

This is a very good answer (I rate it for you) that I was ready to share too. I used to have a German toy - a wire-remote submarine that had exactly this solution. Very simple, cheap and effective. Actually, I believe this question was posed before on CR4 and I provided the same (overlooked) solution. Laboratory stirrers are also a good example that this design works beautifully.

Michael

Can you mount the motor in a small plastic instrument box, with the shaft coming out through a 2-3 mm hole.

After smearing the shaft with a smidgen of grahite grease, make a bead of silicon caulking compound around the shaft, filling up the space between the shaft and the hole in the box and spreading the silicon around each side of the hole to form a grommet.

Once set you may have to turn the motor shaft by hand or with an electric drill to loosen it up, but it should make quite a reasonable seal against water.

Seal the box lid with silicon compound.

Encase in silicone, fill with baby oil.

If the application is for fresh water and it is not intended to last forever, you don't need to waterproof it as long as the voltage is 12V or below. You will loose some efficiency from water drag and may make a bit of hydrogen but it may work for a surprisingly long period. It might be easier to replace the motor every few months (depending on usage) than to try to seal it. I once used a car fan motor as a submerged boat motor and it worked for most of the summer a few hours a week.

I thank u for your valuable suggestions. unfortunately these were some of the ideas that i tried implementing but failed in due course of time. more over the techniques generated a lot of heat burning off the motors. the ones I am using are brushed DC motors that were drawing currents in the range of 2.7mAh. I havnt tried out the magnetic coupling technique suggested as yet. Another suggestion i have received isto couple the shaft to a 4mm dia shaft via a gear set up. it seams there are oil seals(not waterseals) available that work equallu well for shallow water applications.

A magnetic coupling is standard in stirrers used in chemical and biological laboratories. It is a well working and long lasting solution. It even can be had in synchronous mode, that your stirrer works at the same frequency you motor does.

If you insist on mechanical coupling, make any kind of adequate seal, and pressurize the motor with an external fan via a plastic pipe. Clumsy.

Here's a thought:

"Plasti-dip" is a brush-on or spray-on soft plastic material that protects from moisture (http://www.plastidip.com/). They also make another product, "Liquid Tape" , that is applied in the same way, but is a rubber-based material, ideal for electrical applications, so it would not only seal your motor, but your electrical contacts as well.

I have not used this personally, but it is supposed to remove cleanly from non-porous surfaces and so could be tried, removed, and checked for water infiltration. The rubber material should make a good seal around the shaft. If the shaft does not turn freely (might require extra manual effort to free it the first time), you could try coating the shaft with silicon oil or some other compatible (non-solvent, non-swelling) lubricant applied to the shaft before coating. I know that Ham radio operators have successfully used this to weatherproof (waterproof?) high-power RF co-axial cable connectors. Their brochure does mention use on "underwater aquarium pumps".

If the coating is sufficiently thin, immersion in water should prevent any heat buildup. Probably not good for use at any significant depth, but if minimum or no air is entrapped (and therefore compressible), it might work at higher pressures as well.

"Liquid Tape" is advertised as used by the US Navy, but of course it does not mention in what applications. Use as a dynamic seal material might prove interesting.