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Re: [PSUBS-MAILIST] Thruster ideas
Joe,
I can answer some of these questions
already.
"---When are magnetic couplers no
longer appropriate (what torque level)?"
There are many factors with using magnetic
coupling. The first is the type of magnets....which we all know the best to use
are Neodymium magnets. These magnets have unbelievable strength and
actually can be dangerous when close together. The second is the proximity of
the couplings(how close the magnets of one coupler are to the other). The
closer....of course the better. The third consideration is the material
separating the couplers. Just different alloys of aluminum can affect the
gauss(magnetic fields of flux). The first step here is taking two rare earth
magnets(Neodymium) and doing some pull test (Yep...you guessed it....... fish
scale) with different thickness of aluminum, stainless, etc. (Any
non-ferrous metal)
Because all of these effect the torque
rating.....it can be pretty complicated to calculate the magnetic coupling
torque maximum. I also have a few neat tricks when it comes to the
coupling....which I won't share at this point, but I promise to share the
information in the future.
"---How much heat energy
needs to be taken away from what amount of power
generation at what
rate?"
This is my take on the situation, if you have a
motor rated at 2200 watts.....and the motor is 85% efficient(brushless DC
motor)....you need to be able to remove the other 15% that will result in
heat. 2200 watts multiplied by 15% equals 330 watts of heat. (This is
based on maximum wattage of a motor I've been looking at......so the motor
would be running full tilt, and maximum load)
Which if you place your hand on a 330 watt light
bulb you would get the picture. But if you have the motor submerged in oil, and
in a heat conductive capsule.....the heat will be removed pretty fast(into the
surrounding water). Oil is an excellent way to remove the heat( a copper
heatsink can also conduct the heat to the enclosure capsule, if oil can not be
used).The key is to take the heat away before it gets a chance to build up(heat
saturation). I think with the motor submerged in oil, in an aluminum
enclosure.....there will be no problems with heat (unless the water surrounding
the sub is 95-100 deg F.)
"---What is appropriate to
fill with oil and, what is not? (can you fill an
AC motor with
oil?"
This is pretty easy.....any motor with
brushes will fail quickly in oil. The reason.......the
oil (must have enough dielectric strength) acts like a dielectric (current flow
inhibitor) and the brushes skip from oil being introduced between them and the
commutator, this will cause the brushes to arc away the commutator extremely
quickly. If you have ever hear of an EDM (Electronic Discharge Machine), it
works on this principle. Do a search if you haven't. Voltage also plays a part,
but I don't think, we would get to the stage, of having too much
voltage......but this is dependant on the voltage, you have planned. But to
answer your question, you can fill an AC (induction)
motor with the correct oil.
There is another problem......submerging a motor in
oil is going to reduce it's no-load speed (Viscosity). The motor will not be as
efficient at higher speeds. The motor will be restricted in it's rotation. The
slower you can turn the motor and get enough thrust .....the better.
Also.....because motors reach their peak efficiency at about half no-load speed,
it is better to find a slow turning motor. I doubt , this is going to happen for
small thrusters, but I think it can be done.....with some loss....and still come
out ahead.
The last problem.....you can't use just any
oil.....the dielectric strength of the oil must be great enough
to encourage the current to go through the winding of the motor, instead of
traveling through the oil itself(Oooo pretty...... liquid
lightning... :-).
I'm sure that created a ton of questions........but
we are getting closer just by discussing it.
James Long
Owner/Designer
Lil Brother LLC
(Instrument Division)
----- Original Message -----
Sent: Saturday, July 28, 2007 5:27 AM
Subject: Re: [PSUBS-MAILIST] Thruster
ideas
James,
This is way ahead of the planned learning curve for me but,
if your going to
hit the grindstone on thrusters, here are some of the
questions stirring in
my mind.
---When are magnetic couplers no
longer appropriate (what torque level)?
---How much heat energy needs to
be taken away from what amount of power
generation at what
rate?
---What is appropriate to fill with oil and, what is not? (can you
fill an
AC motor with oil?).
I wouldn't worry so much about the prop
direction issue, your solution seems
correct and, working field examples
show it to be not too much of a worry.
Joe
>From: "Lil
Brother LLC" <lil_brother_llc@bellsouth.net>
>Reply-To: personal_submersibles@psubs.org
>To: <personal_submersibles@psubs.org>
>Subject: Re: [PSUBS-MAILIST] Thruster ideas
>Date: Sat,
28 Jul 2007 01:08:52 -0500
>
>Well,
>
>It didn't take
long....and I've run into a snag.
>
>Here is the problem....and I
would like opinions of the best choice....and
>it is a
choice.
>
>Props are optimized to thrust in one direction. Which
direction would be
>the
>best for thrusters?
>
>I
figure forward for a horizontal thruster.....what about a vertical
one?
>
>My thinking is ofcourse thrusting (pushing water)
down.....giving you an
>upward movement.
>
>This discussion is
for fixed thrusters not movable ones. Movable would be
>optimum, but life
doesn't always work that way.
>
>If anyone disagrees please let your
ideas be known,
>
>James Long
>Owner/Designer
>Lil
Brother LLC (Instrument Division)
>----- Original Message
-----
>From: "Lil Brother LLC" <lil_brother_llc@bellsouth.net>
>To: <personal_submersibles@psubs.org>
>Sent: Friday, July 27, 2007 5:10 PM
>Subject:
[PSUBS-MAILIST] Thruster ideas
>
>
>I'm working on some
ideas....and would like to know how many people would
>be
>interested in the design.
>
>The thrusters will
probably start off small, but they should be the
>following (pending
research):
>
>1. Approximately the thrust of the ones used on the
K-350.
>
>2. Magnetically coupled shaft (reduced shaft
pressure)
>
>3. Oil filled. (Greater depth capacity) I know some
oils that I believe can
>be used that are not environmentally
hazardous.
>
>4. Phased type motors, so the controls will be more
complex.
>
>Let me know your thoughts,
>
>James
Long
>Owner/Designer
>Lil Brother LLC (Instrument
Division)
>
>
>
>
>
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