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Old Nov 04, 2005, 06:21 PM
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A cheap submarine motor/ballast pump from an odd source

I came across this rather odd solution to a scratch build problem recently.

A friend of mine wanted a small, low powered motor and pump to use in a motorised conversion of a new scale plastic U boat kit - to make it a displacement diver as well as RC/motorised. (He is a bit of a submarine nutter)

Given that the hull size is small to say the least - he looked on the project as "only a bit of a challenge".

He needed a ballast pump/motor - using low amps and of small dimensions to fit the hull cross section.

The answer was found in a "Home Medical Supplies" store - a battery powered, electric blood pressure monitor (the sort with an inflatable rubber cuff) - when stripped down provided an ideal low voltage battery powered motor/pump assembly to fit in the hull.
Cost about 12 !!

I suspect this could be used in other areas of modelling too - ?home made smoke unit?
Would it be possible to control the speed of the motor via the esc circuitry - and thus blow more or less smoke using the pump as an air blower across the smoke maker as revs change?

I was wondering also if the motor/impeller from a cordless hand held vacuum cleaner (?Dust Buster type) whose batteries are past it might have a use?

Has anyone else come across odd solutions?
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Old Nov 04, 2005, 09:27 PM
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Some people have been using the small BP cuff and motor for years in subs, it's known as the RCABS.
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Old Nov 05, 2005, 07:16 AM
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The Dustbuster blowers tend to be be low pressure, high volume fans that pull lots of amps on low volts (3.6v iirc).
Veering slightly off the subject to LARGE water pumps... Jeff Churill has been using inexpensive bilge pumps for 1:1 pleasure craft, < $20 each and run on 12v, to pump ballast water in his big freighters.
And I've recently noticed some 12v electric coolant circulation pumps used in some automobiles, usually to maintain heater water flow in certain conditions... Lincoln LS used one, Ford Escape Hybrid uses a couple... probably $$$ at the dealer, but maybe in the junkyard someday?

Pat M
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Old Aug 20, 2006, 09:50 PM
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For price it is pretty hard to beat a universal washer pump for autos. They will pump a very decent amount of water in a very decent amount of time.

I realise this is a sort of aged thread and I don't have much interest in boats, bilges, impellers and such but I had a silly dream last night that had me using a motorised toy water gun to propell a very small kayak anong softly and stealthily. Now what I had was quiet but did not have anything for speed. I began to think that I have the knowledge to wind my own CDrom motors and that if I were to replace the motor in the water gun I could actually get some speed out of this thing. I thought further ( stupid dream ) that instead of hopping up the water gun I should instead build a propulsion sytem for the boat. That would be even more efficient!

Since I had that dream I thought I would just poke around a bit and see about what modelers are doing with jet drives. Not that I want to actually want to build what was in my dream but see what really is going on.

I did a search for impeller and that lead me to this particular thread.

Can anyone enlighten me or should I have looked in racing?

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Old Aug 20, 2006, 11:30 PM
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A 'jet' is more or less just a 'ducted-fan' type impeller with a very long 'duct', sort of. A typical prop sort of re-shaped to fit in a properly sized 'duct' ought to give you some push. Whether or not it would be enough is a different story, I have no idea. The 'biggy' would be the clearance tolerances blade/duct. A drive shaft long enough to reach through the 'curve's of the duct to the prop ought to be a nice challange! lol
- 'Doc
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