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RE: [PSUBS-MAILIST] Pressure compensation
Gary,
I've actually compensated a drive train in this way before. Granted it
wasn't a trolling motor but it did work in my application. I used a high
viscosity oil made from fish (so it was biodegradable which fit with the
rules of the competition I was in). It smelled terrible, but it was cheap
and worked really well. Unfortunately, it was discovered that you still
need do put on some sort of compensation device (we used a sturdy balloon)
because it is very difficult to get all of the air out of the system and
even the tiny bubbles will contract and suck some water through the seal if
you don't. However, the balloon only needs to be very small. It actually
improved the efficiency of our drive train because it lubricated all the
parts (there were lots of gears and no long shafts). Anyways, the point is
if the losses aren't too significant it is a very simple and very cheap way
of fixing the problem.
Wade
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Gary R.
Boucher
Sent: Friday, August 11, 2000 11:23 PM
To: personal_submersibles@psubs.org
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