Re: [PSUBS-MAILIST] Pressure compensation

["Gary R. Boucher" <protek@shreve.net>]

     It could work if high enough in power.  But you do have the 120 volt 
in water issue.  I feel like it would be easier and more efficient 
(possibly safer) to compensate a trolling motor.  You wouldn't have to 
worry about the brushes wearing out.

>What about using the motor from a submersible pump?  Granted it will no
>doubt be AC, but you could use a relativaly cheap inverter as long as the
>amperage was not too high.
>Big Dave
>
>-----Original Message-----
>From: Gary R. Boucher <protek@shreve.net>
>To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
>Date: Friday, August 11, 2000 11:31 PM
>Subject: 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
> >