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    Prop shaft seals

    david f
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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  david f Sat Dec 10, 2011 4:49 pm

    Just an update on my Simrit seal arrangements.This is the arrangement on the U Class - ORP Dzik:
    Prop shaft seals - Page 2 Orp_dz10

    You can just see the Simrit seal on the port side shaft.
    A ball race is fitted just under the Simrit seal.
    You can also see the connectors for the universal joints.
    All fairly crude but quite easy to make and works well.
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    Prop shaft seals - Page 2 Empty is the design you describe more or less energy efficient that a shaft seal (battery life)?

    Post  tarheel Fri Feb 24, 2012 5:19 am

    Hermann wrote:Hello David,

    yes, the 7 dark circles you can see on the disc rotor are magnets indeed. They are very common ferrite magnets normally intended to hold/ stick sheets of paper at metal blackboards at the wall. These magnets have a special direction of polarisation, they are polarised in direction of the diameter so the half circle beneath the "aequator" is a south pole, the half circle above is a north pole. So the rotor (and the moulded stator also) has 14 poles. I took ferrite magnets because they had been easy to purchase (in 1993 when I built the first motor, rare earth magnets were hardly available for me). The energy density is much less compared to rare earth magnets but they are full resistant to corrosion in water.

    It's not a magnetic coupling between two magnetic rotors (one inside, the other outside the pressure hull) but a real brushless DC motor where the inner rotor is replaced by a stator system equipped with coils and driven by switching transistors. That stator system (that narrow light grey ring) is attached to the aluminium motor housing and moulded with epoxy glued. The control electronics is located inside the cylindrical motor housing that is screwed to the rear wall of the pressure hull with its flange.

    The motor has 4 terminals: 2 for power spply from the battery and 2 (signal and return) for connection to the radio control receiver.

    And you can see - there is no seal for the 5mm propeller shaft. The whole rear section of the model is free flooded.

    On the photograph you can also see the rods for moving the rudder blades. They are actuated by linear magnetic couplers, also eliminating sliding seals.

    I must confess that this is an exotic practice and a some modellers here called me mad for doing this, but why not doing things in an unusual way? That hermetical concept was just an idea and I wanted to prove that it works.

    Kind regards
    Hermann


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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  profesorul Fri Feb 24, 2012 11:35 am

    @HERMANN,
    Where can be found those magnets like in the picture?. I think they can be used into a lots of aplication don"t You think?.
    REGARDS
    MARIUS
    Giovanni LiCalsi
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    Prop shaft seals - Page 2 Empty Help Converting Graupner MC-19 to 75MHz

    Post  Giovanni LiCalsi Sat Feb 25, 2012 2:23 am

    There must be someone brilliant here that can give me a wiring schematic drawing to convert my Graupner MC-19 to use a 75MHz radio module?
    I'm desperately wanting to convert.
    Thank you,
    Giovanni
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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  nigele(ADMIN)2 Sat Feb 25, 2012 10:27 am

    Hi Giovanni,
    Sounds like a question for John Robinson,put a post on his page.
    nigele.
    Hermann
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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  Hermann Sat Feb 25, 2012 3:38 pm

    Hello everyone,

    (especially Marius and tarheel to answer your questlions)

    @Marius: The magnets I have used for the magnetic rudder couplers were samples I had got from a dealer on who had been on a model exhibition selling various electronic components, tools and so on... This had been more than 10 years ago (you can see it by the coin on the photograph for size comparison, a former DM, since 2002 we have the EURO).
    Meanwhile you can buy powerful magnets in various sizes for example from ebay (look for "Neodym magnets") for almost reasonable prices. But note: for applications where they are exposed to water you shall protect them from water contact by some moulding (e.g. epoxy glue) because if their nickel plating is injured (fine cracks in the surface) the magnet material beneath the plating will start to corrode rapidly.

    @tarheel: Efficiency is a question of running speed, whether the friction of the seal or the "water friction" of a wet running rotor is more lossy. For higher rpm speed a conventional shaft seal will have less losses in comparison to a wet running motor. A wet running rotor is stirring the water around and those water whirls (that do not help for propulsion)cause losses as well.
    But the real advantage of the wet running motor is the tightness, there is no leakage at all even at extreme diving depths.

    Kind regards
    Hermann


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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  david f Mon Dec 03, 2012 12:03 pm

    I've just been referring Dave from Model Boats Mayhem onto this thread and I just realise that all the shaft sealing solutions are a bit "home brewed".

    Can anyone recommend a commercially available "off the shelf" shaft seal system??
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    Post  profesorul Mon Dec 03, 2012 12:38 pm

    @HERMANN,

    Thank You Very Much for the answer and Information.
    I think these type of transmission can be used especially for the small Sub,where the friction is low,due to the small diameter of the shaft,and from heare,the small angular speed,and the propeller speed is also low!.
    Is only My opinion.

    MARIUS
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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  david f Tue Dec 04, 2012 12:17 pm

    I have just had a quick look at the Engel website and all they seem to offer is the Simmering oil seal. Good, yes but was hoping to see a housing to make it more "off the shelf".

    David
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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  david f Tue Sep 30, 2014 9:41 am

    Just a word on how to fit "Simrit" type oil seals.

    As an oil seal they are designed to fit into a machined inset i.e the outer circumference is a push fit into the housing.

    You can fit them this way but you can also use the "sandwich" method I showed earlier or I have even heard of them being glued onto the outside of the WTC. The main consideration are to not use up too much of your valuable WTC space (length mainly). I have found them to be very low maintenance items - they seem to last for years.

    I have always used a ball race bearing immediately behind the seal and I think that this is a good idea to keep the shaft well aligned.

    Don't forget that you will also need some form of "thrust bearing" to take up the thrust of going into forwards or reverse. I use Collets fixed onto the shaft with grub screws. (Aircraft people use them a lot, so available from these sources.)

    I have standardized on 4mm stainless steel shafts for everything (prop shafts, push rods etc.)

    David
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    Prop shaft seals - Page 2 Empty Re: Prop shaft seals

    Post  timgarrod Thu Jun 29, 2017 9:38 pm

    like the idea of the magnet linkages
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    Post  david f Mon Jul 03, 2017 9:44 am

    They do look good for a lot of different reasons:

    - quick to connect linkages
    - completely water tight shaft seals (deep diving?)

    Having said that I haven't tried any yet.

    David
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    Post  merriman Mon Apr 16, 2018 4:07 pm

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    Post  timgarrod Mon Apr 16, 2018 4:59 pm

    very nice. just finished making mine for the gato.

    fingers crossed they work :)
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    Post  merriman Mon Apr 16, 2018 6:08 pm

    timgarrod wrote:very nice. just finished making mine for the gato.

    fingers crossed they work :)

    If I can help with any specifics, just shout out.

    David
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    Post  david f Tue Apr 17, 2018 9:55 am

    Lovely work, David!

    David
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    Post  SimonH Sun Aug 01, 2021 11:34 am

    Whilst not at the sophistication of 'merriman' I thought I would add some notes on some tests on my prototype ideas, though all based on others ideas.
    Using a standard 4mm shaft I opted for a 4x9x3 seal from Simply Bearings @ £2.55 each. As I was already using M10 brass machine screws for the ball race housing I simply bored a 9mm x 3mm recess in the screw head. However, for simplicity I decided to use the screw as a plain brass bearing as the speed is low due to a 9:1 reduction belt drive. Also the M10 is about the right size to fit into a length of hose pipe to do a pressusre test using mains water. Much higher pressure than the 1m or so max depth I'm envisaging.

    Prop shaft seals - Page 2 Dsc02810

    Prop shaft seals - Page 2 Dsc02812


    The 2 x M3 tapped holes are intended for a keeper plate, but due to enthusiasm I drilled right through, they should be blind. Also, I think in the actual boat I will reverse the seal so the head is on the outside and probably not bother with a keeper as the pressure will keep it in. In fact even with mains water pressure and a simple 9mm driled hole the seal is a tight fit and showed no inclination to come out. Simply bearings can supply a 4x8x3 seal but it has an outer metal body and is a lot more expensive (£8) so I'm sticking with the 4x9x3 I think.

    I was intending to use the same seals for the control rods, but the friction is quite high so I then decided to test the design based on silicon tubing thats been discussed.
    Again I used an M10 machine screw as the body, but used 2mm ID x 0.225mm wall brass tube as a guide for the nominal 2mm control rods (actually 1.75mm). I tried 2 sizes of silicon tube 1.5mm ID x 0.5mm thick and 1.5mm ID x 0.75mm thick both from Advanced Fluid Solutions. I decided against the thinner wall as it seemd to stretch more and I was worried about it tearing.
    Prop shaft seals - Page 2 Dsc02811

    The guide tube is simply soft soldered into the M10 screw, it was a bit loose for glue. The length of free tubing providing the actual seal was about 3mm, but back in the hosepipe test it showed no signs of leakage so thats my seal designs sorted!
    For the actual boat I intend to use an M6 machine screw as the body, again with the head on the outside.

    As an aside, rather than various sealing compounds to seal the bolts into the WTC end caps I intend to use M6 & M10 Dowty seals (bonded washers) as they are designed for high pressure and are reasonably cheap, about £0.30 from Advanced Fluid Solutions. Thats one of the reasons I decided to have the machine screw heads on the outside as I can simply put a Dowty seal between the head and the end cap.

    I've mentioined the suppliers where I got my supplies from but I'm sure there are others and folks wil have their own favourates.

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    Post  david f Wed Aug 11, 2021 9:05 am

    Thanks for a very elegant take on sealing issues.

    Those Dowty seals are new to me and I bought some (M8 ones) to try out:

    Prop shaft seals - Page 2 20210810

    They look very good. Better than slathering silicone rubber on and better than rubber washers. They will presumably seal at up to hydraulic system pressures. Although I hope it never comes to that!

    Thanks for sharing.

    David

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