Re: [PSUBS-MAILIST] motor seals

["D. Blake" <dblake@bright.net>]

Gary:
What I meant was a condition of out -of-roundness in which the motor
assembly and the prop assembly are not lined up correctly producing unwanted
vibration from oscillation.  This is echoed by Wade's concerns.  The magnets
may be strong enough to insure an allignment, but more likely a design
should be implemented to insure that all components remain on the same
plane.  The comments made by Sean and yourself are extremely relevant to
what I had in mind from my search on the net.  Consider this article
synopsis:
Article Found:
            Journal of Sound and Vibration, June 1995, Volume 183, Issue 3,
            Article jsvi.1995.0264 (5667 words)


                        Summary / Abstract
            Title: A method of vibration control of a
            magnetic coupling carrying a rotor in a fluid
            with large system variations
            Synopsis: This study is concerned with a
            magnetic coupling in which a shielding wall
            exists between coupling discs. The follower
            shaft carries a rotor in a fluid, and a driving
            torque given by a servomotor is transmitted to
            the follower passing through the shielding wall
            without contact. Analyses are presented of this
            coupling and a method of control for
            accelerating a shaft with a magnetic coupling
            carrying a rotor in a fluid. Since the coupling
            torque of the magnetic coupling is small, the
            transmission is broken when the inertia and
            friction forces become large. To maintain a safe
            connection of the coupling and prevent
            vibrations, a feedforward control method can be
            applied. But this method cannot be applied when
            the system varies. Hence, a method is presented
            of robust control which is applicable to a
            magnetic coupling with large system variations
            during acceleration. To validate the analysis
            and the control method, experimental tests have
            been carried out for some typical cases.

You probably have access to this article at your University.  I know OU on
this end subscribes to the journal, but I cannot get a copy because of a
lack of transportation to Athens.  Check it out if you get time.
Big Dave

-----Original Message-----
From: Gary R. Boucher <protek@shreve.net>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Wednesday, August 16, 2000 12:52 PM
Subject: Re: [PSUBS-MAILIST] motor seals


>     I think that sometimes with pumps the impellers are magnetic in which
>case the unbalanced condition could exist.  Is that what you are referring
>to?  The prop would have to be on a shaft that had bearings for support.
>
>GB
>
>At 09:37 AM 8/16/00 , you wrote:
>>Wade, Gary, and All:
>>After reviewing a little info on this type of coupling, I noticed a
concern
>>with "vibtation" and "centering" from the manufacturer.  These are areas
to
>>be overcome by thoughtful design.  The prop assembly would have to be
>>located in such a way as to maintain center to avoid vibration. Another
>>thing I thought I would mention is that the shafts on these motors can be
>>pressed out and replaced very easily.  I bulit them for years while
working
>>in a motor factory.  The shaft bodies are knurled, and then pressed into
the
>>armature.  If need be, a custom shaft could be easily machined on a small
>>lathe that would better utilize thrust bearings, allow necessary length
for
>>the coupling, and provide the possibility for improvement in outside
>>housing/endcaps, etc.  Of course this implies practically creating a
>>thruster from scratch using only the 'guts' from an existing motor, but it
>>sure would be a great addition to a psub!
>>Big Dave
>>-----Original Message-----
>>From: Wade Carson <wacarson@interchange.ubc.ca>
>>To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
>>Date: Wednesday, August 16, 2000 10:02 AM
>>Subject: RE: [PSUBS-MAILIST] motor seals
>>
>>
>> >Gary,
>> >Would the magnets be effective enough in shear to maintain a useful
>> >coupling?  I have no knowledge or experience in this area, but I do know
>>the
>> >easiest way to get two magnets apart is to slide them sideways.
>> >
>> >Wade
>> >