RE: [PSUBS-MAILIST] external Motors for depths of 1000ft

["Graham K" <cryogenicz@dsl-only.net>]

do you know the best motor to use for this?

Thanks for this helpful information, I will do this modification! Do you
know any other modification to do?

Thanks!!!

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Phil Nuytten
Sent: Monday, June 17, 2002 8:01 PM
To: INTERNET:personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] external Motors for depths of 1000ft


Hi, Graham:
        Well . . . a couple of mods - you should drill and tap the housing
in a couple of spots - at same distance from either end, but 90 degrees
apart ( or something like 90 degrees - more or less if fins/ power conduit
are in the way).- tap for a small size thread - 1/8" NPT is fine - install
a couple of (1/8" male to hose barb) brass fittings and clamp a pigtail of
clear Tygon tubing to these fittings. The rotor  will pump the comp oil
through this tubing and you can inspect it as part of your pre/post dive
checks. It is readily apparent when the oil is becoming contaminated from
the carbon brushes. When it is discolored, it needs to replaced as it will
eventually become conductive, causing the utmost suprise to your motor!
This is not a big job and once you get a feel for how many hours it will
run before fouling, you can make the 'oil-change' part of the standard
routine maintenance schedule. The reason for the pigtail is to use the
Tygon as a mini comp system to make up very minor oil loss through the
lip/cup/chevron shaft seal.( due to minor weepage or major temperature
change) Otherwise, the seal will pass salt water to make up any volume
deficiency and that water will travel through the oil as the sub changes
position - and that is no bueno. Actually, you need to look at the
particular trolling motor body design and place one fitting adjacent to the
rotor and one in a quiet 'back-water' area - this will ensure some exchange
thru' the Tygon, each dive. The Tygon is also handy to do the oil change -
use a large plastic syringe full of oil with a snout that you can insert
into the Tygon - or, a 'collapsible' plastic bottle (courrugated) with a
catsup/mustard snout works well. Remember that there must be no air spaces,
so you need to comp the power conduit also.
        Also be aware that the brushes may 'float' from centrifugal force
in the denser- than- air  comp oil. This is easily corrected with heavier
springs or keep the revs lower than would be  usual in a dry motor.
        Or . . . go to a brushless PM motor and eliminate float and
contamination. Or buy a super/duper Nuytco thruster such as we use on the
'DeepWorkers' ( we have them built for us by an OEM in the UK) a mere 7 or
8 grand will get you the thruster plus the control cards, etc. Lloyds
certified, full pressure tested, connectors, whips, pentrators. etc. Hmmmm
. . .well, maybe not.
        Anyhow . . .trolling motors for submarines are like lead acid
batteries  . . inefficient as hell compared to more sophisticated systems,
but cheap as Borscht, easily replaced, available everywhere, and will do
the job. You may only get half the running time on a comparable set of
batteries (since trolling motors can draw twice the amps for a given
thrust) but, so what? Four hours instead of eight hours for one tenth the
price? - sounds like a hell of a deal to me!
Phil Nuytten