Re: [PSUBS-MAILIST] Thruster ideas

James,

You paid attention in "A" school....didn't you! :)

What you say about heat exchange, confirms my thoughts on the matter. However......

"...........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... :-).........."

Now, this "liquid lightning" thing...is a bit troublesome. I fully understand the brushes, and viscosity issues but, If one were to flood an AC motor with oil and find it to be a mistake, could this be undone?

You asked me about my maneuvering thruster design, which will be DC and, based on what I come up with over the next several years in my workshop for the ROV. But, the main motors for NR-2, are a different story.

My thinking is to make these AC on order to run directly off the gen-set surfaced and, be more efficient battery wise submerged as suggested by Jay. These would be based on pods similar to the K-350 but, appropriately sized and asked to do continuous duty in surface transits while intermittent duty submerged.. The location outside, makes cooling a snap if I can fill these with oil.

So to oil or not to oil...that is the question. I need to do more reading on this. Thank you, your information was valuable!

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 23:12:25 -0500

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 -----
From: "Joseph Perkel" <joeperkel@hotmail.com>

To: <personal_submersibles@psubs.org>

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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