[PSUBS-MAILIST] Oil Compensator

Wed Apr 5 20:00:04 EDT 2017

Hi Hank,
By "finding a bushing for the propeller shaft that is lubricated by the
water" do you mean the bearings which will sit outside the pressure housing?

I started looking into ceramic bearings for just this application, and they
were interesting - ie. some of them have no metal parts and little need for
lubrication.

Cheers,
Steve

On Thu, Apr 6, 2017 at 9:47 AM, hank pronk via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Sean,
> I think one of us should develop a magnetic coupler in kit form.  Maybe
> if there is an interest with potential sales it could become a reality.  I
> have come close to starting and even bought the magnets.  My stumbling
> block is finding a bushing for the propeller shaft that is lubricated by
> the water.
> Hank
>
>
> On Wednesday, April 5, 2017 5:29 PM, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>
> I've decided to go with the   PSF - 20 cSt Silicone Bath Fluid for my
> motors.
>
> http://www.clearcoproducts.com/pure-silicone-low-viscosity.html
>
>
> Brian
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alan James via Personal_Submersibles <personal_submersibles at psubs.
> org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.
> org>
> Subject: Re: [PSUBS-MAILIST] Oil Compensator
> Date: Wed, 5 Apr 2017 22:48:50 +0000 (UTC)
>
> Jon,
> I don't know whether you have followed, but I have made a brushless 2000W
> thruster
> which I trialed in a pool for 30 hrs. The glue on the hall sensor board
> melted
> & it stopped because the timing went out. Apparently the glue was designed
> to melt
> so people could adjust the timing. The thruster got hot because the
> compensating oil
> was being forced away from the motor through centrifugal force, & up the
> wiring tube.
> If I had an overpressure on the system I could have prevented this, but
> didn't think it
> was needed in a few feet of water. I was running this motor with 2 lip
> seals with ambient
> pressure in between, but have purchased a mechanical seal for the next
> version.
>    It had a comparable or better thrust to Watt ratio than a lot of the
> advertised ratings
> of commercial thrusters.
>    I think it is a matter of time before Minn kota put out a brushless
> thruster if they haven't
> yet. Most of the commercial ROV & submarine thrusters are now brushless.
>    If there was enough room to fit a mechanical seal on a Minn kota it
> would be a big
> improvement. The white paper suggests grinding the Minn kota shaft to a
> specific
> finish, with matching bearing & seal, however a mechanical seal is more
> tolerant of
> the shaft surface finish & you could avoid this.
>    Re the heat; one concern is transferring heat off the windings, which
> oil compensating
> will do 100 times better than air. However Minn kota motors would have
> large gauge windings
> that can cope with the heat.
> Below is a 2010 thread by Carsten dealing with expansion.
> Alan
>
> Alan and the other gentlemens,
>
> our expierence with oil filled motors, batterys or even propeller shafts is that the oil expand if the motor is runing longer time.
> Simple because its warm up. We had that problem on Eurosub on the first dives.
> And on Euronaut we filled the bladder complet up and the get pretty hard in the hot summer just by sun heating the sub.
> A full filled bladder with over pressure creates a lot of interal
> pressure in the wrong direct - a lot of force for the bladder itself and hose work.
>
> Therefore our bladder are only half expand during the filling. But still free of any air.
> An other point is that the bladder has to be not to small.
>
> To create a slightly overpressure on the motorseal you just install the bladder below the motorcasing.
> But we found out that on trolling motor (electric outboards) this is not nessesary. There seals are good for some
> douzend feets at least - so you can install the bladder else were.
> Filling is simpler if the bladder is slightly over the motor - you can vent the system direct on the filling point.
>
> Another point is that we install now one bladder per motor  - in the earlier sub (Sgt.Peppers) we install a central
> one for all motors. Hard to find a leak after a dive with all the T-crossing piepings and motorseals..
>
> vbr Carsten
>
>
>
>
>
>
> ------------------------------
> *From:* Jon Wallace via Personal_Submersibles <
> personal_submersibles at psubs.org>
> *To:* Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> *Sent:* Thursday, April 6, 2017 8:31 AM
> *Subject:* Re: [PSUBS-MAILIST] Oil Compensator
>
> Hi Alan,
>
> Yeah, that white paper pretty much just states fill it with oil and you're
> good to go.  It doesn't address some of the issues that have come up on the
> list regarding heat and expansion, inter-seal cavity, etc.  I understand
> the drive to find a perfect solution and that minn-kota oil compensation is
> not perfect, I'm just trying to understand the real-world ramifications of
> using it as that white paper suggests and most psubbers have implemented.
> Given that water is such a good heat sink, are the heat and expansion
> issues of the oil really that serious?  I know Alec wrote something about
> his experience with this some time ago but am having a hard time finding
> that thread.  Pretty sure SNOOPY is still using simple oil compensation
> regardless.
>
> Jon
>
>
> On 4/5/2017 4:02 PM, Alan James via Personal_Submersibles wrote:
>
> Jon,
> Cliff has been doing a lot of work on Minn kota modifications & has the
> hands
> on experience. If he's not tuning in it would be worth contacting him
> privately.
> The Minn-kota seal set up is not ideal, with the gap between the two seals
> meaning one or the other seals will fail when their pressure rating is
> exceeded.
> The outer seal seems to serve a double purpose, being the first line of
> defense
> against water ingress & also a sacrificial seal that will see all the
> abrasive muck stirred up by the prop.
> Noticed in this kit that the outer seal has a shield to protect it.
> Historically in deep diving set ups they have had dual seals, but with
> either ambient pressure between them,
> or a cascaded pressure system, and normally mechanical seals. The outer
> seal was regarded as sacrificial.
>    Maybe you could pack between the seals with grease to reduce the air
> gap.
> I am not sure whether you could simply reverse the inner seal or not as
> they need a shoulder that the pressure
> will push them up against.
> Cliff is using a small relieving air regulator to compensate his motors.
> The regulator is fed air from your tanks
> & is set at an overpressure of about 4psi. The regulator is orientated
> upside down as the relieving air feeds
> out through the handle portion & the orientation will stop water entering
> when this valve opens.
> This system was suggested by Hugh, & Cliff is trialing it. It has the
> advantage that you could either air or oil
> compensate. If your motor ran out of oil it would just be replaced with
> air above ambient pressure.
> I am not sure at what pressure the relieving valve opens.
>    There is this very good Psub resource from an expert in modifying Minn
> kotas for underwater use.
>
>
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