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Re: [PSUBS-MAILIST] Pressure compensation

Jon,
     You're right in that the mentioned method is a much better way of 
compensating.  I wonder if anyone has ever been successful at using a low 
viscosity oil in a trolling motor.  It would be an interesting experiment 
in the direction of a low cost compensated thruster.  It almost makes me 
want to go get a trolling motor and experiment.  I wonder if the armature 
would have too much drag against the oil and how much power you would loose 
in the process.  I would think that cooling would not be a big problem.  I 
would suspect that real thrusters for submersibles that are compensated in 
this way have special armatures.  Probably the same oil used in submersible 
pump applications would work.

GB

At 08:16 PM 8/11/00 , you wrote:
>On Fri, 11 Aug 2000 22:00:37 -0700, "Gary R. Boucher" <protek@shreve.net>
>wrote:
>
> >      The trick is having the pressure inside the motor the same as the
> > outside pressure, or at least close.  If you set the pressure inside the
> > motor at a certain value and ascended the pressure inside is greater than
> > outside.  If you dove beyond the set pressure you have more pressure
> > outside.  One method of pressure compensating a motor is to place a rubber
> > bladder with air in the water close to the motor and run a tube from the
> > bladder to the motor housing.  As the sub dives the pressure on the 
> bladder
> > increases and so does the inside motor pressure.
>
>Just as a point of interest...
>
>In deep professional-quality thrusters, they typically fill the thruster
>housing (and thus the motor) with oil, which makes the whole deal basically
>non-compressable. Instead of using a seal, they use a magnetic coupling to
>turn the propeller. This gives a thruster that can be used to full ocean
>depths.
>
>Later,
>Jon
>
>--------------------------------------------------------------
>    Jon Hylands      Jon@huv.com      http://www.huv.com/jon
>
>   Project: Micro Seeker (Micro Autonomous Underwater Vehicle)
>            http://www.huv.com