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Author Topic: Piston Tank advice  (Read 14004 times)

mermod

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Re: Piston Tank advice
« Reply #50 on: June 17, 2014, 01:28:52 pm »

David,I'm surprised the Lipos lived, I've had a few issues with lipos over the years but mostly in planes, as for the gearboxes, I would love to use MFA but I'm unsure of what to get and I have a lot of r/c spares laying around (one of the benefits of once owning a hobby shop) but most of them are ex monster truck parts, the main spur gear is from a Traxxas Emaxx monster truck!
So far I've only lost one sub, my little deep dive 6, she was ballasted quite low and I think it developed a small leak and decided It was happy on the bottom, where I sail is tidal so I went back after a few hours only to find some kid had discovered it and promptly unscrewed the hatch and filled the rest of it with water, when I pried it from his clammy little hands I discovered the speed controller and battery were still hissing giving me visions of exploding Nimh's and lawsuits.
The Typhoon came about after watching The Hunt for Red October one too many times ( I believe you also suffer this illness ) started her about 14 years ago so pre internet, only information was the Dragon plastic kit so I scaled it up, made the plug from MDF then molded in fibreglass, then got married, had kids, opened a business, had some surgery, so on and so forth so she's not as shiny as she was in the photos anymore.

Phill
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Subculture

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Re: Piston Tank advice
« Reply #51 on: June 17, 2014, 03:34:37 pm »

I recently was given a  pair of 750ml 6 volt Engel tanks. These have 540 motors fitted as standard which wind about 10500RPM unloaded and are geared down about 17.5:1.

The pistons are 70mm diameter, and the motors draw about 12 watts a piece running against no pressure, and that increases to about 25 watts at about one atmosphere pressure.

I am modifying them by trimming them down to 500ml, as none of my models require 1500ml of ballast, and converting them to 12 volt operation, but using smaller 385 motors. These work at about the same RPM as the 500's but weigh half as much, take up less room and are a bit more efficient.

mermod

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Re: Piston Tank advice
« Reply #52 on: June 18, 2014, 01:02:31 pm »

Did a check on the capacity of my tank today, 1.25 litres and it runs beautifully on a 7.4v lipo :)
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Re: Piston Tank advice
« Reply #53 on: June 18, 2014, 01:15:24 pm »

That's good to know.

Building you own gearbox is a bit more effort I guess, but does give you a bit more flexibility with regards to the ratio you select.

mermod

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Re: Piston Tank advice
« Reply #54 on: June 22, 2014, 07:58:34 am »

Just a quick update, here's some pics of the finished end caps, laser cut from 10 and 3 mm acrylic.

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mermod

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Re: Piston Tank advice
« Reply #55 on: June 22, 2014, 08:02:00 am »

a quick test fit of all the bits shows it needs just a little tweaking.

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Re: Piston Tank advice
« Reply #56 on: June 22, 2014, 11:07:53 am »

Looks nice. Looks like you have you put an o-ring at the motor end cap too?

mermod

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Re: Piston Tank advice
« Reply #57 on: June 22, 2014, 11:28:20 am »

Yeah, just in case any water gets past the plunger, just paranoid I guess.

Phill
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Re: Piston Tank advice
« Reply #58 on: June 22, 2014, 04:53:20 pm »

Have you sealed the spindle too?

profesorul

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Re: Piston Tank advice
« Reply #59 on: June 22, 2014, 07:29:03 pm »

@ Subculture ,
 
Do You think is possible to do such thing ?.
 
MARIUS
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Re: Piston Tank advice
« Reply #60 on: June 22, 2014, 10:35:02 pm »

Ron Perrott builds his tanks with a fixed spindle and the piston runs up and down on the thread with a glanded nut. This avoids having to make space for the retracting rod.

Not necessary on this tank though, just highlighting that water leaking through the seal will make it's way past the spindle even though the endcap is sealed. I have seen a  piston tank seal fail, just the once, and it was on a very old engel boat. The tubing developed a blister for some reason. The boat shipped a bit of water but not enough to sink it thankfully.

mermod

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Re: Piston Tank advice
« Reply #61 on: June 22, 2014, 11:19:28 pm »

Its more of a guard against a small slow leak, once there is enough water to reach the spindle obviously I would be in trouble (not that its going to happen anyway)

Phill
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mermod

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Re: Piston Tank advice
« Reply #62 on: June 24, 2014, 12:21:51 pm »

Funny thing is, I ran it this afternoon with the new caps and it struggled like crazy to get even halfway, turns out my seal on the rear end is watertight but sadly also airtight so it couldn't compress, when I drilled the hole for the end stop plunger and released the pressure all was good.

Phill
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mermod

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Re: Piston Tank advice
« Reply #63 on: June 24, 2014, 12:26:38 pm »

Nearly there :)




Phill
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Davy1

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Re: Piston Tank advice
« Reply #64 on: June 25, 2014, 02:16:58 pm »

Hi Phil,

Many thanks for the very good photos. I can't quite see,  but are you using a ball race on the spindle? If not, it obviously works well without them but I have used them in both my tanks and they seem to be commonly used in German practice. Reduces friction.

Concerning shaft seals and endcap seals - not much scope for those I'm afraid.You are going to have to allow the WTC to pressurise anyway. This can be a problem with a small WTC and twin piston tanks.

Shaft seals on a threaded shaft are a very tall order. There have been various claims about their effectiveness (Ron and Nigel) but I think that the jury is still out in terms of their reliability in the long run.

Anyway I've rambled on long enough, your tanks look very good!

David
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mermod

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Re: Piston Tank advice
« Reply #65 on: June 26, 2014, 02:33:18 am »

Thanks David, if you look very closely at the black spur gear you can just see one of the ballraces peeking out on the left.

Phill
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Davy1

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Re: Piston Tank advice
« Reply #66 on: June 26, 2014, 09:03:01 am »

Hi Phill,

That's great. Thanks for pointing it out.

David
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mermod

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Re: Piston Tank advice
« Reply #67 on: June 26, 2014, 10:23:41 am »

Here she is pictured today, as you can see she's a bit grungy but its all automotive paint so it should scrub up OK,



Phill
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mermod

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Re: Piston Tank advice
« Reply #68 on: June 26, 2014, 10:28:48 am »

And a shot of the insides with the aluminium hatch behind.





Phill
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derekwarner

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Re: Piston Tank advice
« Reply #69 on: June 26, 2014, 10:48:36 am »

 ;)....& mermod says....... 'as you can see she's a bit grungy...... but it should scrub up OK'

Don't worry Phill........even real subs get a bit grungy in dock  O0.........a bit of spit & polish at the end of the refit & all will be fine :-)).........Derek
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mermod

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Re: Piston Tank advice
« Reply #70 on: June 26, 2014, 10:53:45 am »

I did want to have a play with some weathering, maybe I should just spray some matt clear over the grunge and leave it alone  :-))

Phill
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Davy1

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Re: Piston Tank advice
« Reply #71 on: July 03, 2014, 09:05:15 am »

Hi Mermod,

A couple of videos of a newly refurbished Darnell Type XXI taken last Sunday. This has the single large piston tank and the video will give you an idea of dive/surface times. You will have more fore and aft control with 2 tanks (There are some more videos/photos over on the Forum.)

http://youtu.be/mPpItPK_ShI
https://www.youtube.com/watch?v=D4S3xeIt6oII

David
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mermod

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Re: Piston Tank advice
« Reply #72 on: July 03, 2014, 12:36:16 pm »

That's very cool, I think I'd be a bit nervous submerging in that murky water.

Phill
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salmon

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Re: Piston Tank advice
« Reply #73 on: July 03, 2014, 02:49:11 pm »

Phil, what happened to the pictures you posted?
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mermod

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Re: Piston Tank advice
« Reply #74 on: July 03, 2014, 11:22:52 pm »

I've had a few issues with my photo hosting site, I will try to get some more pics up when I can.

Phill
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