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Author Topic: will a brushless motor work underwater.  (Read 9909 times)

Ian Robins

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will a brushless motor work underwater.
« on: July 18, 2010, 08:56:27 AM »

hi all,
 
as the above question says. will a brushless motor work under water. ie. completely under water but not waterprooffed.

i am thinking to put a brushless motor into a mini-sub as a thruster, but not enclosed in the hull.
the speed control will be inside the dry hull but the motors wont be.
I understand the metal bits will rust but how long will it work for.

ro88o0
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Timo2

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Re: will a brushless motor work underwater.
« Reply #1 on: July 18, 2010, 09:22:48 AM »

Hi

      YES

 Check out   http://www.rcgroups.com/forums/showthread.php?t=522762&highlight=pod+drive&page=517

   post 7741

     Timo2

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malcolmfrary

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Re: will a brushless motor work underwater.
« Reply #2 on: July 18, 2010, 10:32:59 AM »

Hi

      YES

 Check out   http://www.rcgroups.com/forums/showthread.php?t=522762&highlight=pod+drive&page=517

   post 7741

     Timo2


Or, to be more accurate, not sure.  The post on that link does show a project using a submerged motor, and does show it working once.  A later post asks how long the motor survives, but there was no reply to that in the next couple of pages.  In salt water, there would be no chance, in regular pond water, exposed metal would need plenty of TLC, in anything but distilled water (possibly even de-ionised water), any exposed electrical connections are going to be liable to electrolytic corrosion.
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dodgy geezer

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Re: will a brushless motor work underwater.
« Reply #3 on: July 18, 2010, 11:03:57 AM »

It's not only brushless - a small brushed motor will work under water. More slowly, because of the drag around the armature. I suspect that you run into worse electrolytic corrosion problems as the motors get bigger and your current goes up...

You can do this once, for a short time, but then you have to disassemble the motor, and clean and dry and oil it. If you take this trouble you can probably do it again - but not too often I guess.. %% %%

If you don't immediately clean and dry, you will need to replace the motor at each outing... :(( :((


I suspect this is not a workable way ahead for a boat which is expected to run more that 10 minutes at a time....
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Timo2

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Re: will a brushless motor work underwater.
« Reply #4 on: July 18, 2010, 11:34:40 AM »

Hi All

  More detail at     http://www.rcgroups.com/forums/showthread.php?t=1091137


   OK the motors need some more TLC   after use


    Timo2     O0
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barriew

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Re: will a brushless motor work underwater.
« Reply #5 on: July 18, 2010, 12:26:37 PM »

A member of my club was telling me just this morning that he always runs in his brushed motors under water :o

Barrie
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dodgy geezer

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Re: will a brushless motor work underwater.
« Reply #6 on: July 18, 2010, 12:46:25 PM »

A member of my club was telling me just this morning that he always runs in his brushed motors under water :o
Barrie

Intentionally?
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stallspeed

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Re: will a brushless motor work underwater.
« Reply #7 on: July 18, 2010, 02:07:45 PM »

Use one which has a sleeve bearing.
Flush it out and dry it after use.Dare I mention WD40 ?
There will be no electrolysis since it is  3-phase A.C.
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barriew

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Re: will a brushless motor work underwater.
« Reply #8 on: July 18, 2010, 02:38:10 PM »

Intentionally?

Yes apparently so :-)

Barrie
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malcolmfrary

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Re: will a brushless motor work underwater.
« Reply #9 on: July 18, 2010, 03:02:43 PM »

Quote
There will be no electrolysis since it is  3-phase A.C.
Well...Yes and No.
Brushless motors are by their nature 3 phase AC.  What they are supplied with from an ESC in a model is re-arranged DC in short pulses.  Any exposed metal that is positive will pass current to the fluid that it is exposed to, and in doing so will part company with some of its substance, generally in the direction of another bit of metal at a different potential.  During the time that it is negative (or more likely battery -ve, usually ground) it will be receiving or being electro-plated, just not necessarily in the same place that material was removed from.  Holes gained rarely fill themselves in, they usually grow.
Just looking at the powerhead in my fishtank, there is a form of brushless inrunner, but the electric bits are well separated from the water while the rotating magnet bit isn't.  However, it was designed with running submerged, but only when mounted vertically.
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geoff p

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Re: will a brushless motor work underwater.
« Reply #10 on: July 18, 2010, 06:45:04 PM »

Many years ago, when I worked in Orkney, we built submersible frames to tow cameras for Fisheries Research.  The motors were standard, off the shelf, 3-phase 440 volts, so they could be speed-controlled and reversed fairly easily, and ran very happily in the nice, cool, salt water of the North Sea.

Geoff

P.S. The films of fish swimming with a trawl net were quite stunning.
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Cornelp

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Re: will a brushless motor work underwater.
« Reply #11 on: July 18, 2010, 08:00:21 PM »

Yes, any motor will work under water without problems... actually better because of the very good cooling. But you will have to be more careful with TLC... I only lost one out the 6 motors i have submerged (4 brushed, two brushless), and that was a small brushed that was already wobbly when i installed it. The oldest is a 2440 inrunner that is still ok after many hours... and yes, WD40 is your best friend. I use it right after taking the model out of the water, and later at home I use some oil on the bearings.
A very good method to break in a motor (brushed) used for cars or boats was to run it a low voltage for some time in water...
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roger

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Re: will a brushless motor work underwater.
« Reply #12 on: July 18, 2010, 09:57:59 PM »

Surely only the terminals will present exposed metal to the water – at least delicate bits of metal with lots of electrons whizzing back and forth, that is – where you might get terminal (pun intended) electrolytic corrosion.  Paint over the terminals and Bob’s your mother’s brother.

I’d steer clear of liberal use of the WD40.  It might eat the plastic bits and soften any glue (almost certainly used to hold the magnets in place amongst other bits).

I suggest that a flush through with deionised water – especially if you are sailing in salty water – should suffice at the poolside.  Follow up with a blow through with circuit cleaner which will displace most of the water.  Back in the workshop, blow-dry with warm air (not hot air … ditto softening the glue) and carefully re-oil all the bearings.  It should last well beyond my boredom limits and a rising yen for something new.
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malcolmfrary

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Re: will a brushless motor work underwater.
« Reply #13 on: July 19, 2010, 10:17:32 AM »

Quote
Paint over the terminals and Bob’s your mother’s brother.
Add to that the cable ends to ensure that there is no chance of water wicking up the strands.  Also make sure that the cable is supported or tied down so that the joint cannot flex, a hairline fracture in the coating is just as bad as a "real" hole.  In this case, electrolytic corrosion doesn't really come into it - its just ordinary chemical corrosion.
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nick_75au

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Re: will a brushless motor work underwater.
« Reply #14 on: July 19, 2010, 11:53:39 AM »

Yes, they will work under water,,,,
they lose efficiency due to the fact of friction of water on the rotating parts, the bearings are not designed for it, run one in salt water so the the black wire syndrome appear in short time and the iron laminations rust. 

I have seen outrunners with the windings encapsulated further with epoxy which will help but you wont get rated power as the epoxy will insulate the motor.

Nick
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Cornelp

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Re: will a brushless motor work underwater.
« Reply #15 on: July 19, 2010, 06:17:05 PM »

One other issue is how long you want this to work... If I can get a 30$ motor to run for 2-3 seasons, I'm satisfied with it. It is very clear that this is not a good application for a brushless (or brushed) motor, but it surely moves lovely...

http://www.youtube.com/watch?v=GJIHZFWSLrU&feature=player_embedded#!
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