underwater motor question

I was recently reading "Build Your Own Underwater Robot" and decided to take the plunge! :-)

The book recommends using Rule Bilge Pumps so I bought three of them figuring that I could strip them down and get a watertight motor.


After cutting open the case, I find that they have those Johnson motors that are common with cordless drills and such.

See pic:

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Good motors, but LOTS of openings for water to get in.

So would anyone have any suggestions for motors that would be a little more suitable for an underwater ROV?

Tanks, DOC

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Trolling motors.

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--As long as it's being used in fresh water I think it doesn't matter too much if it gets wet. IIRC there was an episode of Junkyard Wars where one team built a "wet" sub and went with a wet motor as well. Gotta be a catch tho; not sure what it is. Probably has to be a brushless motor or something..

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I've heard filling the motor case with oil works. A bit of drag but it keeps out the water and compensates for the pressure.

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Some AC motors are constructed in way that the rotor runs in water and the coils stay dry. E.g. circulation pumps for central heating (asynchronous) or small fountain pumps (synchronous). Maybe you can modify an existing asynchronous motor with by impregnating them wih resin. Not sure what to do with the bearings :-(

One of the other posters mentioned to run the motor in oil. From my past experience in well logging, I know that water will creep between fat and metal eventually (but here we are talking depths off 3 km)


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Wim Ton

You're thinking of brushless motors. The most common type available are computer fans. You can remove the fan and cast resin around the coils to make them waterproof, but they don't have much power when running in the water. And they're not reversable so they're pretty useless for an ROV. All you really need to do with the bearings on those is to use a good thick grease.

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Jeff H........

Lies, All lies. Don't believe a word Difool/sayNO says. He fears the truth!

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Jeff Holinski

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