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Author Topic: Welman build  (Read 17997 times)

salmon

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Re: Welman build
« Reply #50 on: December 18, 2012, 05:09:34 pm »

Well done! When I built my Gato, the song "The First Cut is the Deepest" kept playing in my head. Look forward to your next posting, keep up the great work.
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If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

bbdave

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Re: Welman build
« Reply #51 on: December 21, 2012, 10:13:15 pm »

The past couple of days have been spent on building up the keel it's hollow to allow for the rudder and plane linkages  bit of build and design this i'm sure i'll fathom it with plenty of bits of brass.


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bbdave

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Re: Welman build
« Reply #52 on: January 04, 2013, 05:53:41 pm »

All is on hold now for 6months or so as the in laws have moved in so i'll be concentrating on making small bits linkages etc so i have it all ready to go when i can work on the main hull again.

dave
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Subculture

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Re: Welman build
« Reply #53 on: January 04, 2013, 09:32:20 pm »

the in laws have moved in

You have my sympathies.

bbdave

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Re: Welman build
« Reply #54 on: February 14, 2013, 04:15:53 pm »

I'm looking at WTC materials i have a couple of choices the usual acrylic tube 3mm wall or aluminium with 1.6mm wall both 90mm O.D. are  there any issues with reception using ali? the price is roughly the same give or take 1 or 2 


Dave
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Re: Welman build
« Reply #55 on: February 14, 2013, 05:03:44 pm »

You will have to run the aerial externally to avoid it being shielded. The aluminium tube will be a bit heavier too, as it's about three times denser than water whereas PMMA is about 1.2-1.5 times depending on if it's been glass filled.

bbdave

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Re: Welman build
« Reply #56 on: February 14, 2013, 05:20:48 pm »

Ok so no real problems then I might go for Ali a nice polished WTC could look good wander if I can find some turned Ali end caps




Dave
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Re: Welman build
« Reply #57 on: February 14, 2013, 05:41:58 pm »

You'll have to make them. Anodizing the tube would be the best way to keep it looking slick. If you polish it it'll probably tranish quickly unless you lacquer it- I found aluminium is very corrosive in water.

bbdave

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Re: Welman build
« Reply #58 on: February 14, 2013, 06:31:49 pm »

It would be specialy if brass is present but I'll deffinatley look into it


Dave
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bbdave

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Re: Welman build
« Reply #59 on: February 14, 2013, 09:52:33 pm »

If I make the end caps when I create the groove for the o ring how much does the o ring need to depress to form a seal?




Dave
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Re: Welman build
« Reply #60 on: February 14, 2013, 10:04:09 pm »

Have you got Norberts book? Tells you in the back appendix the right dimensions for the sizes you are likely to use in a sub.

In case you haven't, assuming the bore is fairly decent you should aim for about 12-15% compression of the o-ring thickness e.g. a 4mm thick o-ring will be squished down about 0.5mm, which would give you 1mm of compression over the diameter, as the ring is compressed on both sides. Maximum compression for an o-ring is generally about 25% of the thickness, but you'll find it very difficult to push the seal home with that level, and you certainly shouldn't require more than 20% unless your bore is very poorly toleranced.

You also need to make the o-ring gap wider so the o-ring can squish into it (the rubber doesn't technically compress it extrudes). So for our 4mm o-ring we would want at least a 4.5mm gap assuming 0.5mm compression, as the ring will expand 0.5mm width wise as it forms an ellipse when squeezed.

You can use Nitrile or silicone o-rings. The latter are softer, but they can be more fragile than nitrile, and they're typically more expensive and a little harder to get hold of.

Does that make sense, or sound like double dutch?

bbdave

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Re: Welman build
« Reply #61 on: February 15, 2013, 05:58:55 am »

No that makes sense i must get hold of Norberts book

Cheers
Dave
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profesorul

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Re: Welman build
« Reply #62 on: February 15, 2013, 03:23:18 pm »

EXCELLENT explanation!.  :-))
 I must say I didn't know how much is going to compresss the O-rings as percentage.I guest make theproperr adjustments several times until I consider is OK,and then tested in the water.So THANK YOU.   :-))
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bbdave

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Re: Welman build
« Reply #63 on: February 27, 2013, 10:15:44 pm »

I have received my acrylic tube today and now trying to figure how to fit everything in if i get a ballast bag of 65mm x 200mm and wrap it round inside the 90mm tube will it fill fully or does it need to be layed flat in the tube?

Dave
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Re: Welman build
« Reply #64 on: February 27, 2013, 10:50:41 pm »

Some leave the bag loose in the cylinder, the Thundertiger neptune is a good example, as is Norbert Bruggens Delta sub.

Some other modellers fit the bag inside a a small cylinder of its own, or in a sealed off section of the main wtc pipe. This helps constrain the bag, plus it can't chafe against other bits and bobs inside the cylinder.

Both systems seem to work well enough, your choice.

Andy

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Re: Welman build
« Reply #65 on: February 28, 2013, 07:07:56 pm »

Thanks i meant if i fold the bag will it still fill ok?.

Dave
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Re: Welman build
« Reply #66 on: February 28, 2013, 08:21:24 pm »

I see. Yes no problem at all.

bbdave

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Re: Welman build
« Reply #67 on: March 02, 2013, 03:56:58 pm »

Ok this is the sixth attempt to post so hopefully the Internal error wont rear it's ugly head this time >>:-( . For the last week or so i have been busy with the hacksaw and file making bits to operate the rudder/dive plane it's all a little Heath Robbinson at the moment but it does seem to work the only thing that needs changing is the UJ from tube type to conventional as the tube allows to much flex which i thought might happen but it was worth a bash but apart from that by jove i think it works.

First off was setting the rudder tube and making the rudder/dive plane
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bbdave

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Re: Welman build
« Reply #68 on: March 02, 2013, 04:02:42 pm »

I hope these pictures explain the controls easier than words the rudder and plane move at the same time turning and diving/surfacing the bottom pivot needed to move in and out in both directions as the arc prevents solid linkages




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Re: Welman build
« Reply #69 on: March 02, 2013, 04:32:38 pm »

That looks good. Perhaps a stiffer piece of tube will remove or at least cut down on the flex. The only other way I can think of would be a crude type of CV joint or a cardan joint of some type.

bbdave

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Re: Welman build
« Reply #70 on: March 02, 2013, 05:07:58 pm »

That's the next plan i can get one the right length but it'll be 2mm wider so hopefully shouldn't look to out of place

Dave
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bbdave

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Re: Welman build
« Reply #71 on: August 07, 2013, 09:27:07 pm »

Well the six months are up we have moved out from the in laws and got sorted in a place of our own so I have resurrected the build and started wet and dry sanding in earnest so not much to show for a bit while this goes on but more time spent now will fingers crossed save hassle later


Dave
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bbdave

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Re: Welman build
« Reply #72 on: August 13, 2013, 09:16:25 pm »

Ok I'm in the process of measuring up the end caps the disc that will hold the o ring works out to be around 77.94 the o rings I can get are either 75.79 or 78.97 which would be a better size to order?




Dave
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Re: Welman build
« Reply #73 on: August 13, 2013, 09:44:55 pm »

You always want a bit of 'snap' on o-rings so that you stretch them slightly to fit. Between 1-5% stretch of the o-ring diameter with about 2% being optimum, but don't sweat too much if you can't get it spot on. So the 75.79 o-rings are your best bet.

Odd sizes- are you buying imperial o-rings?

derekwarner

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Re: Welman build
« Reply #74 on: August 13, 2013, 10:46:50 pm »

Dave..........mmmmm 75.79 x 3.53 section is a standard 2-234 series o-ring
Technically it should fit a shaft of 76.2 or a bore of 82.55....however these are listed for 250 Bar hydraulic applications and your use is very low in pressure....1 to 1.5 Bar? so the o-rings will not be pressure energised
O-rings are forgiving and will stretch..........but it is the cavity sizing that should provide approx. 10% crush for these low pressure applications.....
Generous angled & smooth lead in chamfers + white petroleum jelly will also help in ensuring you don't shave or shear the o-ring during installation.....Derek
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Derek Warner

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