Re: [PSUBS-MAILIST] External Motors for depths of 1000ft

["Captain Nemo" <vulcania@hawaii.rr.com>]

Harry,

You might want to read my white paper about Minn Kotas, seals, and such in
the PSUBS design guide section.  Might answer some questions for you.

Pat


----- Original Message -----
From: "Harry Spillett" <harry.spillett@bigfoot.com>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, June 18, 2002 12:35 AM
Subject: [PSUBS-MAILIST] External Motors for depths of 1000ft


> Hi Guys,
>
> Sorry to go back to basics!
>
> When you pressure compensate a motor our other external "void" with oil or
> HP air, is this literally the only thing you have to do or are their other
> considerations you must take into account?
>
> I think that I read some where that the Deeprover had a number of oil
filled
> junction boxes at various points around the outside of the hull, do you
just
> top them off through a couple of valves or do the innards have to be
> "prepared" first?
>
> The same question applies to lead acid batteries which have been toped of
> with oil. Does it have to be a particular Varity and what other mods need
to
> be done the terminals / top up slots?
>
> Finally, if a motor or similar is pressure compensated with HP air does
this
> need some sort of regulator like a SCUBA rig sot that it varies  amount of
> "compensation" as you change depth? Or is the motor housing modified with
> new seals etc to with stand the higher internal pressure when at the
> surface?
>
> As you can tell I am waiting by the letter box for my Busby!
>
> Harry
>
>  -----Original Message-----
> From: owner-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org]  On Behalf Of Phil Nuytten
> Sent: Tuesday, June 18, 2002 4:01 AM
> 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
>