For high power deep work they use hydraulic prop motors.  There is a
central hydraulic pump with an oil filled electric motor.  Those systems
are usually 10 to 1000 horsepower.
My company (Imetrix) uses electric 1/2hp to 1hp off-the-self
magnetically coupled thrusters.  They have an electric motor & gearbox
which spins permanent magnets in an air filled stainless steel cup.
Magnets outside the cup drive the prop.  If we had to custom build
something the pancake motor idea might work.  For a model the VCR motor
might be a place to start.

Sherpa Doug

> -----Original Message-----
> From: Peter L. Peres [mailto:plp@ACTCOM.CO.IL]
> Sent: Tuesday, July 31, 2001 1:17 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT]: Underwater robots
>
>
> > seals
>
> One of the easyier ways is to have normal (almost) capsulated motors
> completely filled with light oil or safe freon. The water
> won't try to get
> in as there will be no pressure differential and usual seals will be
> enough. An equalizer membrane is usually necessary for
> thermal expansion
> and such. The motors need to be run slower. In theory there is an
> increased danger of explosion (not implosion) with this but
> if you go into
> deep water you live dangerously anyway.
>
> Peter
>
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