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Re: [PSUBS-MAILIST] Thruster ideas
James,
I like the improved efficiency on brushless motors (do they really convert that efficiently?). However, your vertical press calc is for the birds, not the fish. Those kind of loads are handled very nicely by thrust bearings, if need be, and if you're going deeper than those bearings can manage, then, of course, your trolling motor isn't the answer. Unless you are going VERY DEEP, in which case, some kind of compensation would alleviate the external squeeze, anyway. Remember, the deeper we go, the more pressure there is, or did you already say that?
As an aside to this, Karl Stanley is running trolling motors, compensated, to 3000 feet, and they seem to work very well. Now, if you can cook up a brushless unit, mag coupled, that cost less than, say, two grand, then you might entice him, especially with the improved efficiency, as he runs a small battery pack, relatively speaking. But, he's using what he knows about, and it's working pretty well by all accounts.
I like more power than that, but it suits him. In fact, I know of several sets of Minn-Kota 101s that have been modified with proper o-ring grooves in the body junctions and a ceramic shaft seal, and were tested to failure (average of 1200 feet in a test tank) and run today, quite effectively, in the 600-700 foot depth range, with little or no problem.
None of that changes the fact that new technology has improved things immensly, and I'm looking forward to hearing about your progress in developing something affordable that might well make all us psub cranks a lot happier. Personally, I'd love to ditch the steel cased monsters on my sub. Need a test bed for your prototype? I'm your man.
Best Regards,
Vance
-----Original Message-----
From: Lil Brother LLC <lil_brother_llc@bellsouth.net>
To: personal_submersibles@psubs.org
Sent: Sun, 29 Jul 2007 5:15 pm
Subject: Re: [PSUBS-MAILIST] Thruster ideas
Vance,
I'm not saying a trolling motor is not designed correctly.(for it's use). But take a trolling motor and place it in a press (vertical press...vertical orientation ........bearing on end of the shaft) Turn it on...and add pressure until it won't move. If you have a pressure gauge and a fsw chart of pressure versus depth...you can now see where the motor will stop working.
Remember...the deeper we go....the more pressure exerted on that shaft trying to push it in the motor (or the seals leaking....)
Also....most trolling motors (not all) are standard brushed motors. When you calculate that they are only 55-65% efficient.....that hurts. A BLDC motor is 80-90% efficient. Battery power goes much further. Put some pressure on it....and I'm sure a trolling motor is even less efficient.
I'm not saying to not use trolling motors.......but for people looking to stay down longer, and have a limited power budget, may want to have some efficient thrusters.
James Long
Owner/Designer
Lil Brother LLC (Instrument Division)
----- Original Message -----
Sent: Sunday, July 29, 2007 3:28 PM
Subject: Re: [PSUBS-MAILIST] Thruster ideas
Ten million trolling motors can't all be wrong (although they have the motor's outer case itself as part of the housing, for more direct distribution of heat). HBOI improves on that by the simple expediant (simple to say, not to do) of machining a base plate replacement for the shaft end of a PM motor. Bearings mount in the divider plate, and the motor casing is assembled on top of it. The stub shaft is spline cut and sticks into the sun gear through the plate. A welded can goes over the top (o-ring seals at the divider plate) and a cast housing mounts to the back, within which is the large shaft with bearings, coupling and seal. The whole thing is aluminum, of course, and bleeds heat exceedingly well. That handy old ultimate heat sink out there in the deep briny never seems to get enough.
And, before you ask, 1.25 HP reduced to 250 or something lets them turn a square tipped four-bladed 14X14 prop in a Kort nozzle--with maybe 80 pounds of thrust-in-motion (not bollard pull, that's probably 100 or a little better). It's old fashioned, I guess, but, as you know, I'm a bigger-and-slower-is-better kind of guy where props are concerned, and I like that torque in the water. Man, I'd love to have some of those babies at 48V. My K-350 would turn every way but inside out. I'd rig it just like the good Dr. Nuyton did on the DWs, and as we discusssed for NR-2 (I think that was about 4 tons ago, or so).
Mind you, Phil's 1 hp rare earth units kick ASS on the Deepworkers, which tells me prop and nozzle design and all the rest has come a long way through the years. At $10,000 a pop, I don't suppose either one of us will get any realtime hands-on experience with them, but it sure do sound good, do it not?
Vance
-----Original Message-----
From: Joseph Perkel <joeperkel@hotmail.com>
To: personal_submersibles@psubs.org
Sent: Sun, 29 Jul 2007 12:59 pm
Subject: Re: [PSUBS-MAILIST] Thruster ideas
James,
I am wondering (and perhaps Vance can speak to this), if "conduction" through the mountings to the external case, is sufficient for a directly immersed air-filled thruster.
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] Diver Lockout.... serious question here!!
Date: Sun, 29 Jul 2007 11:08:27 -0500
Vance,
Air is the least effective means to cool something that is enclosed. The problem with air, if it is exchanged in a fast enough rate, it works great. On the other hand....if you can't exchange the air, you end up with an oven. Oil on the other hand can carry more heat away faster. The density is the factor here. Air is not very dense, so it will only absorb so much thermal energy per unit.Oil will absorb many more btu per unit than air. Also because oil will thermocycle.....the oil will transfer the heat to the container that contains it faster.
I think an air filled thruster would work good too, but there are problems with compression. If there are any bearings housed within the casing......they will bind under extreme pressure if filled with air. An oil filled enclosure will not compress as far. There will still be compression problems, but not to the extent of an air filled unit.
There was a project a few years ago....a guy made a gaming computer that used oil to keep all the expensive parts cool. You should look it up. It worked really well. (Oil cooled computer)
I do not plan at this point to run a reduction gear. BLDC motors are real good at direct drive.
I would like to build smaller thrusters that can go very deep.
James Long
Owner/Designer
Lil Brother LLC (Instrument Division)
----- Original Message -----
Sent: Sunday, July 29, 2007 8:55 AM
Subject: Re: [PSUBS-MAILIST] Diver Lockout.... serious question here!!
James,
Serious DLOs have dive chambers separate from the crew compartment. And as for your thrusters, in my experience AIR transmits heat faster than oil. How deep are you building these things for? HBOI, for instance, runs aluminum cans and PM motors in air to 3000 feet, with no real problems. The commercial units that Nuytco uses ARE oil filled, I believe, but have a higher pressure rating, and no reduction gear.
I've got into some pretty serious questions lately......and I've done a
little reading about diver lockout (archives), but the archives raised a
question.
If you have a 1 atm sub, with a diver lockout........how do you lock a diver
back in?
Are there any 1 atm subs with a lockout?
If there are......if the lockout has been pressurized to the outside
pressure........what method is used to depressurize it back to 1 atm?
(these questions are redundant I know)
And the last....the important one.....is this on the dangerous side? If you
depressurize to fast......the bends.
I was reading about the nice sub.....(the Krata I think.....please don't
quote me ....I've had a very long two days)......but I didn't notice if it
was 1 atm or not.
Some one learn me on this. :-)
(Hey....at least I know what a VBT is for now.)
James Long
Owner/Designer
Lil Brother LLC (Instrument Division)
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