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Hi,
I have a few idea's involving propulsion underwater for recreational divers
and was trolling through the internet searching for readily available
propulsion motors that would withstand the pressures exerted at a maximum of
40 metres depth. I came across the PSUBS site and was quite excited when I
saw the research and developments you guys have done. I am very intrigued as
to how much thrust (in terms of bollard pull) can be obtained from the
trolling motors and what sort of power consumption they use. The power
consumption is of concern due to weight restrictions, I can probably get
away with eight or ten 12volt 1.2 amp/hr batteries linked giving maybe 10 to
12 amp/hr total. I have a few idea's of my own involving making a housing
and using a battery drill which should be within scope amp/hr wise for a
duration of around 90 minutes, however the seal arrangement would be my
downfall.
I am actually serving on a British Royal Navy re-supply ship down in the
south Atlantic at the moment and have access to some decent machine tools
here as well as at home in my own workshop in the UK. The Guys on here think
I'm a little crazy spending most of my time playing with bits of metal and
toying with broken things from the ship. I like to try and make something
diving related from the bits of scrap lying around and have successfully
made a video camera housing from an old CO2 fire extinguisher, tested to a
depth of 40 meters.
Obviously the sealing arrangement on the trolling motors are of some sort of
rubber lip seal, I was wondering however whether a mechanical seal could be
used? Steel against a carbon faced ring perhaps? I know we use this kind of
seal in most of the main sea water pumps down in the engineroom on this fine
vessel (he laughs at the 'fine vessel' comment) However there is minimal
pressure involved, perhaps 3 bar at most, not enough for 40 meters. No-one
here can tell me a max pressure for a seal of this type. Do you have any
experience?
I was especially interested where you mention the use of transformer oil in
the motor housing. Obviously this will take a lot of strain away from the
seal arrangement due the hydraulic effect. Love that thinking, however the
transformer oil is a high resistance fluid, I don't see how this works with
the contact between the brushes and the comutator. Is there a degree of loss
in power? If I were to adopt this theory in my own build using the drill
motor mentioned before would I have to use some special brushes as I have
been told the oil sometimes makes the brushes crumble depending on type?
The section I found on the web was quite old and I'm not even sure you'll
get this and make any sense of it, but any help or advice you can give is
much appreciated. If you do indeed get this I am sorry for asking so many
questions in one hit. I am quite eager to make progress with my idea which
will look something like the picture below. I know I could probably go out
and buy a finished item that looks something like it already but half the
fun for a gadget freak like me is making it in the first place.
Many thanks
Steve Bell LH(E) RFA Gold Rover.
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