Model Boat Mayhem

Dry Dock / Shipyard: Builds & Questions => Submarines => Topic started by: mermod on June 01, 2014, 09:00:04 AM

Title: Piston Tank advice
Post by: mermod on June 01, 2014, 09:00:04 AM
I need a bit of advice from some submarine experts, I'm having a go at making my own using gearing from an RC car, so far it works quite well but I have noticed after 20 or so cycles that the threaded rod seems to be getting sharper on the thread even though the action is smooth, also the motor seems to be working harder than I would normally like, the current motor is a 550 with a 19tooth pinion but I am considering using 2 low drain 540 motors and maybe dropping down in pinion size, thoughts?
My other option is to lose the piston tanks and just go for the mini aircompressor type of system although I do like the thought of a tank either end for balance instead of one big one in the centre

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2099_zps0fc8d25f.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2099_zps0fc8d25f.jpg.html)

Here was my original setup but it was sooooo slow, took a minute and a half to fill but had plenty of power thanks to the gearhead.
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2090_zpsdeca38ac.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2090_zpsdeca38ac.jpg.html)
Title: Re: Piston Tank advice
Post by: derekwarner on June 01, 2014, 09:11:52 AM
mermod....I know zilch about submarines :D ....but ask

1. what is the threaded rod diameter sizing [M10...M12] & material?.....
2. what is the corresponding nut material?
3. what is the ratio of nut length to diameter?
4. if it is Grade 304 on Grade 304........both components are scrap ....anti galling paste is too late for these items
5. a bronze nut with a length ratio of x 3 on the diameter with a new threaded rod will assist with a light lithium based lubricant

Derek
Title: Re: Piston Tank advice
Post by: mermod on June 01, 2014, 09:46:57 AM
Hi Derek, I will do my best but I'm just a guy mucking about in the shed.
1. the threaded rod is stainless 12mm unknown grade
2. the nut is about 45mm long and just steel but it has that bronzey look about it
3. nut length to diameter sounds a bit personal  {-)
4. not sure what 304 is and have never heard of anti galling but it sounds painful
5. would lithium grease help with the current materials and is the sharpening effect a normal thing?

I really appreciate your help as I'm feeling a bit out of my depth here (pun intended)

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 01, 2014, 11:04:49 AM
The gearing looks a little tall to me. The previous version had too much gearing by the sounds of it.

The motor you're using looks more than large enough for the application, although the RPM may be higher than optimum. You could perhaps get away with the taller gearing if you used a lower revving motor.

What Derek mentioned is in relation to moving parts using stainless on stainless causing unacceptable wear, and can in fact cause cold welding of parts under extreme cases. You need a sacrificial part, either the nut or the threaded rod, so that one wears whilst the other does not (or wears very slowly). Some of the German modellers recommend using a brass threaded rod, as it's easier to replace than the nut- which usually has to be custom machined.

Anti-galling paste is usually a copper based grease, which effectively puts a coating of softer metal between the surfaces. Of course that only lasts a while as it wears off, so it's probably not a lasting solution , but more the kind of thing for assembly of parts.

Mild steel studding will wear much better than stainless BTW.
Title: Re: Piston Tank advice
Post by: mermod on June 01, 2014, 11:42:46 AM
Thanks for that Subculture, I think I can get hold of brass threaded rod, might give that a shot and make that the weak point (don't want to re machine that nut) as far as the gearing I might get hold of some smaller pinions and try that as trying to source some decent motor/gearboxes is proving difficult.
What would your thoughts be on scrapping the pistons and going with the tyre inflator type compressor system with a solid wall tank like the old Eden subs? seems pretty bullet proof, keeping in mind my sub is a 1.8 metre typhoon, really shouldn't have started watching  my traplet rc sub DVD should I:)

Phill
Title: Re: Piston Tank advice
Post by: U-33 on June 01, 2014, 12:10:48 PM
Just a thought...but have you considered using a screenwash pump, filling/emptying a sealed tank? Nothing technical about it, use a servo tripping two microswitches..one to fill the tank, one to empty it.




Rich
Title: Re: Piston Tank advice
Post by: mermod on June 01, 2014, 12:31:35 PM
I quite like the idea of a single reversible pump but apparently I need something called a hydraulic valve and I don't know why or where to get one, OTW submarines have a system like that.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 01, 2014, 12:59:52 PM
I would persevere with the piston tanks, they give the best control of ballast, and no exposed water surface to reduce stability. Looks like you're doing a good job, just needs a little refining here and there.

MFA do a good range of geared motors, and ebay is also a good place to find cheap motor/gearbox combinations, although the latter aren't always as well documented, so you need to know what you're buying.

It's fairly easy to calculate motor wattage and RPM needed for a given filling/emptying time provided you know the piston diameter and pitch of thread, plus the depth you wish to be able to empty your tanks at.

To give an idea of power engel tanks, which use a reasonably sized 70mm piston only need about 12 watts to empty and fill, and that only increases to about 25 watts at about one atmosphere compression. This compares favourably with pump systems in terms of efficiency.

Typical filling time is about 15-20 seconds and they have sufficient reserve to compress to  two atmospheres, although at that pressure they do become very inefficient as you are getting close to stalling the motors.
Title: Re: Piston Tank advice
Post by: david48 on June 01, 2014, 01:18:10 PM
The thread that is for something that has a load to move is usually an acme or butters thread ,have a look at G cramps or screw type car jacks this type of thread won't feather due to the cut angle of the thread.Finding a size to suit your use might be something else.
David.
Title: Re: Piston Tank advice
Post by: derekwarner on June 01, 2014, 02:07:04 PM
mermod .... stainless steel blends are many...

1. the family termed as the Grade 300 Series are austenitic  ;) which means non magnetic, generally......this also suggests non rusting
2. the lower number in the Grade 300 family also determines by content <*< being a more easily machineable material
3. you certainly will not find a Grade 300 series length of 12 mm diameter pre machined acme or buttress thread profiles .....

David......these threadform profiles have little to do with load moving or feathering but with compressive strength or load tightening O0

4. 12 mm diameter pre-machined [rolled thread] brass rod is readily available
5. I would prefer not to ask for any further references to your nut length  {-), however suffice to suggest a ratio of 3.75:1 is more than adequate......OK?  O0
6. OK ....one last request........ :embarrassed: place a magnet on your nut  ;) if the nut is not attracted to the magnet....the nut is machined from Grade 30X? material

Derek
Title: Re: Piston Tank advice
Post by: Subculture on June 01, 2014, 06:39:22 PM
V-thread stock is higher in friction than square or Acme threads, but it's inexpensive and readily available as studding. All piston tanks I've seen are made using normal v-thread bar. If they wore out with quickly I think their owners would soon be looking for alternatives.

In a nutshell if the thread is wearing out quickly it's either a combination of materials and/or a misalignment in the mechanism resulting in mechanical binding.
Title: Re: Piston Tank advice
Post by: Davy1 on June 02, 2014, 10:23:13 AM
Hi Mermod,

Sometimes Forums can give you too much advice  and I would stick with the approach you are using with the piston tanks. You are going to get there and once you have piston tanks you will not want to go back to any other dive system.

You have already solved some of the most significant problems - the piston and seal and the drive system. (BTW I can now see on your photos that you are using microswitches as limit switches - fine.)

Adding to what we have already  talked about on the AMS Forum, I have been using two home made piston tanks, very similar to your own, for the last 2 years on my subs (last used at Barrow yesterday). Polycarbonate piston, O ring seal, aluminium cylinder. I would recommend a stainless steel shaft but with a brass driver. (All these are pretty much as used by German modellers - the home of piston tanks, really.) I use MFA geared motors on both tanks - they are good.

I would tend to stick with a high gear ratio - a slow piston tank is no huge problem and it makes any later proportional control simpler. That is the only extra refinement I have fitted compared with yours - proportional control, but lots of people use piston tanks without this.

Keep on at it - you are nearly there!

David
Title: Re: Piston Tank advice
Post by: Subculture on June 02, 2014, 04:44:02 PM
One thing to watch for is the o-ring compression. Too much increases friction a lot. The general advice is about 10% of the o-ring thickness, and a maximum of 15%. I done some tests of my own and found o-rings are quite a bit higher in friction (more than double) than the pneumatic seals used by Engel and Airzet rings sold by Freudenberg. The snag with the special seals is limited availability and cost. The Engel seals are also rather fat, which increases the length of the tank. Not a major issue in a large boat but could be a problem in smaller vessels.

Seal friction is relatively minor when compared with water pressure however, and it is much alleviated things get wet (behave yourself!).

A good empircal test for your tank is to block off the outlet and run the tank to half full. If it can't get there relatively effortlessly, then it's underpowered or under geared.
Title: Re: Piston Tank advice
Post by: mermod on June 03, 2014, 12:02:51 AM
I must admit, I cheated when it came to the piston and seal, I had a friend that worked at a hydraulic ram manufacturer a few years back, he took it to their machinist who was ex navy and told him it was for a 1.8m long model military sub, he was more than happy to help :)
Title: Re: Piston Tank advice
Post by: Subculture on June 03, 2014, 09:45:39 AM
If your machinist friend sized the groove for hydraulic applications, then it's likely to have too much squeeze on the ring, as hydraulic pressures are typically much higher than the kind of duty our models will require.
Title: Re: Piston Tank advice
Post by: mermod on June 03, 2014, 11:53:02 AM
I made sure that the guy was aware that I was only using it in water, I had a play with the existing setup today and it seemed to run a lot smoother than the other day, I might get hold of some smaller pinions and try that first before I revert to the slower motor/gearbox setup again.
Title: Re: Piston Tank advice
Post by: Subculture on June 03, 2014, 12:20:37 PM
What are the dimensions of the tank e.g. diameter and spindle length?
Title: Re: Piston Tank advice
Post by: mermod on June 04, 2014, 05:09:46 AM
Derek, I placed a magnet on my nuts today :o and they stick,
Subculture, the note that came with my O rings says BS148 70 DURO, the maximum length of travel, so face of the piston to the back of the end cap is 315mm, the ID of my pipe is 73.74mm and the piston itself is 73.6.
I ordered a couple of sets of pinion gears to play with today so that will be interesting.

Phill
Title: Re: Piston Tank advice
Post by: derekwarner on June 04, 2014, 05:37:11 AM
Mermod......

1. the geometry for BS2-148 sounds the best law of fit
2. 2.148 = 69.52 ID with a nominal wall of 2.62 = 74.14 so a crush of 0.2 per side is OK here
3. 70 duro in your application is preferable to the other option of 90 duro  :-))
4. you may well find it advantageous to smear the o-ring with clear Vaseline for improved lubricity
5. at the pressures & speeds you will be using....it will not was off

Derek
Title: Re: Piston Tank advice
Post by: mermod on June 04, 2014, 07:26:36 AM
I have been using a product called rubber grease, is that ok for this situation?

Phill
Title: Re: Piston Tank advice
Post by: derekwarner on June 04, 2014, 08:34:26 AM
Yes mermod..... :-))
Title: Re: Piston Tank advice
Post by: Subculture on June 04, 2014, 10:15:14 AM
Plugged a few numbers into a spreadsheet I made up. This uses the formulas in Norbert Bruggens book.

This is what it spat out. Based on an M12 thread with 1.75mm pitch for the tank to fill in about 18 seconds (about equivalent to engel tanks) you require a motor that can make about 45 watts and which is geared to produce a spindle speed of 600 RPM under load. Such a combination should also enable the tank to empty at a pressure of 0.8 bar or about 12 psi.

The motor shown looks like a Traxxas Titan 550 buggy motor, and I would hazard a guess that it's the 21 turn model. This will make 45 watts easily but will be high revving, so I think you'll be undergeared with any practically sized single stage gearbox.

Looking at your pictures it looks like the present gearing is about 4 or 5:1? I'd say you need more along the lines of 15:1 or possibly higher.
Title: Re: Piston Tank advice
Post by: mermod on June 04, 2014, 11:20:15 AM
Thanks for that, and I must say, I'm impressed that you deciphered Model Submarine Technology, I gave up and just look at the pretty pictures :)

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 04, 2014, 11:39:16 AM
I understand- I know that book gives people a lot of headaches, but is a valuable reference tool.

The thing that gave me most problems when that book first came out, was knowing where to get stuff.

What's a simmerring I thought, and where do I get one. Internet wasn't much cop back in the mid-nineties. No google then!

The equations were less of a problem, really just Newtonian mechanics, although there are one or two errors in the book which doesn't help.

Once you sort them out however they do make it easier to select appropriate components.

If you're a Facebook member the spreadsheet is available to download on the Dive-in FB page along with lots of other interesting articles and information.

Feedback indicated that it's still too complicated. Oh well, don't think I can't make it any simpler.
Title: Re: Piston Tank advice
Post by: mermod on June 04, 2014, 11:55:46 AM
I can relate to having trouble sourcing stuff, try living on an island off the coast of Australia, I mostly have to rely on local engineering supplies and just hope they don't ask what its for as I usually get some stupid comment and a snigger, I'm lucky in a way in that I used to run a hobby shop so I know where to get most standard items (hence why I use buggy motors and gearing) but  other than that its the net and I still don't like using credit cards on line (old fashioned I know)
As for equations, I'm a cabinetmaker so I can build you a traditional solid timber roll top desk, do your shopfitting or fit out your kitchen or fishing trawler but don't ask me to do equations.
Oh, and I will be finding the Dive-in FB page asap
Thanks again

Phill
Title: Re: Piston Tank advice
Post by: vnkiwi on June 04, 2014, 12:03:39 PM
Hi Phil,
You got it bad, you should try living on that other Island group, just east of you.
Sub stuff, the proverbial hen's teeth over here.
cheers
vnkiwi
Title: Re: Piston Tank advice
Post by: Subculture on June 04, 2014, 12:05:05 PM
I get all my stuff from the internet now. Mainly ebay. It works well for me, because I know what I'm looking for, but it must be a bit of a nightmare for newcomers.

Model shops rarely have the items a model submariner needs, and local engineering suppliers have all but vanished in London- high business rates and land costs have pushed industry out of the capital.
Title: Re: Piston Tank advice
Post by: mermod on June 05, 2014, 01:28:15 AM
Just a thought, the titan 550 is quite high revving, how about a 55t or35t rockcrawler motor? keeps it simple and compact but with way more torque and much lower revs, think I have a couple hiding in the shed, I might give them a try when my pinions turn up.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 05, 2014, 09:50:13 AM
I think the 55t motor would be an improvement, but still too fast on your existing gearing. They tend to be about 1000RPM per volt, so assuming you're running 12 volt system that would give 12000RPM or thereabouts. Even at half volts things will probably be too fast.

Bearing in mind you want an unloaded shaft speed of about 750RPM (loaded 600RPM) you will need a gearing of 16:1, which is difficult to achieve in a compact form with single stage gearing. If you change to two stage gearing all you need is a two lots of 4:1 gearing, which is quite easy to achieve.

I am wondering what the gear reduction was on the motor/gearbox combo you said was too slow? Perhaps if you substituted a higher revving motor onto that gearbox, or used a taller pinion on the output shaft so it had less reduction, assuming the motor has enough beans to pull a taller drive.
Title: Re: Piston Tank advice
Post by: mermod on June 05, 2014, 12:12:12 PM
Before I continue, thanks so much for taking the time to help guys, it's very much appreciated.
I hunted down some specs on the original motor and gbox and I believe its this one http://www.jaycar.com.au/productView.asp?ID=YG2738
also, the main gear with the nut in it is a traxxas spur gear which is a 66T 55dia, If I change back to the original motor/gbox I do have a couple of kyosho gears I could modify 1x 43T 45mmdia and a 39T 40mmdia.
To be honest I never thought the old girl would hit the water, she's been sitting around for about 12/13 years, back when there was a submarine group in Launceston they used to refer to her as the spider catcher.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 05, 2014, 01:57:17 PM
No wonder it took a while to work the tank, 50:1 internal gearing plus the external gearing of about 3:1 gives 150:1- far too much gearing. With that sort of reduction you could run a rack and pinion, not a jack screw!

The motor is a very low revving unit at about 2750RPM with a torque rating of about 1kg.cm. If those figures are accurate, with your 19t pinion and 66t main gear attached directly to the motor shaft (remove the 50:1 gearbox) you should get something very close to what you're aiming for.
Title: Re: Piston Tank advice
Post by: mermod on June 07, 2014, 11:25:38 AM
I will give that a try when the new pinions arrive, also I had a bit of luck today, on a shopping trip to Launceston I dropped into a shop called Nuts & Bolts Tasmania, absolute model submariners heaven........10mm brass threaded rod, hex couplers for turning up the spinning nut in stainless and nothing was too much trouble, could have spent lots more in there and probably will before I'm finished.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 07, 2014, 11:56:07 AM
A 10mm thread will have a finer pitch 1.5mm which will improve reduction but slow the tank down a bit.

If you have a 12 tooth pinion, that would give you better torque on the combination above, with a spindle speed of 500RPM. Filling speed should still be quite reasonable at 24 seconds with an M10 thread.
Title: Re: Piston Tank advice
Post by: mermod on June 07, 2014, 12:24:36 PM
Thanks, the pinion set I have coming has a 9,10,11,12,13 and 14 so I can experiment a bit, hard part is going to be removing those lovely reduction boxes just to use the motor but I suppose that's better than them in a draw and the sub on the shelf.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 07, 2014, 02:59:20 PM
That should give you plenty of flexibility.

The gearboxes can be a pain, chiefly because they tend to press on the pinion gear. I file one side down then it tends to relax the interference fit and you can pull the pinion off with a pair of stout pliers.
Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 04:50:51 AM
Ok, so my pinions have turned up and I've had a bit more of a play, while going through my bits and pieces I found some ex aero 3:1 reduction boxes so I bolted on a 540 motor (EM407 6-12v 13,000 rpm ) then popped a 13T pinion on the gbox output shaft and bolted it onto the tank with the existing screw gear, speed seems spot on, motor gets warm not hot, 3.5 amp draw empty and up to 5amp with a finger blocking the end, by the time it gets to five the plunger is about 3/4 up, so I think I'm pretty close, only downside is that its noisy.
One question I do have is what size inlet/outlet is normal, seems a larger hole would cause less drag on the system.

Phill
Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 04:51:32 AM
Nearly forgot the picture.
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2101_zps30e41afd.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2101_zps30e41afd.jpg.html)
Title: Re: Piston Tank advice
Post by: Davy1 on June 17, 2014, 09:54:08 AM
Hi Phil,
I think you are almost there. Current draw is fine if fairly high (but maybe your tank is fast and big.) You could control that current with an H bridge switcher if you ever want to.

I use a 4mm internal diameter outlet with no problems but again maybe your tank will be bigger & faster. You could measure the outlet pressure at the tank or maybe try different outlet sizes and monitor the current.

I have rather lost the plot with your gearing, what with all the discussions. What is your OVERALL reduction now?

Don't worry about noise. You will not hear an thing underwater. (Unless you use a hydrophone!)
Your are nearly there. Congratulations - I have hardly seen anyone in the UK using a home made piston tank. Lots in Germany.

David
Title: Re: Piston Tank advice
Post by: Subculture on June 17, 2014, 10:01:35 AM
15.23:1 by my reckoning, so unloaded spindle speed should be about 850 rpm.

Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 10:07:44 AM
Thanks for that Subculture, I had also lost the plot on what the gearing was, is 850rpm ok? only thing that concerns me is I cant see how the nylon pinion is attached in the 3:1 aero box, hope it doesn't come adrift.

Thanks again

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 17, 2014, 10:18:57 AM
Sounds good to me. You could afford to come down a bit in RPM if you want, that will lower the draw on the motor at the expense of a longer fill time. However it sounds like the motor is coping easily if it can push against over 45psi.

Looking at he picture I think that the plastic gear may be moulded onto a metal splined hub. Shouldn't provide any problems.
Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 10:45:52 AM
I just gave it a quick go on 6v and I'm even happier now, smoother quieter and still a good fill speed, I will stick an amp meter on it in the morning and check the draw on 6v.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 17, 2014, 10:57:34 AM
Halving the volts will significantly lower the wattage of the motor. you should expect to see roughly half the current you originally had. However sounds like you had more power than required anyway. I'd try the 'finger over the tube ' test again, providing the motor can drive the tank half way without too much trouble you'll be fine.
Title: Re: Piston Tank advice
Post by: Davy1 on June 17, 2014, 11:16:35 AM
Hi Phil,

Do you confirm 15:1 ?

I wouldn't go any lower than that. ( I take it you are going for a fairly rapid fill tank. )

The 6v or 12v or choice needs to be also taken in view of the rest of your submarine design. Type of battery, drive motor etc. I have always found that 12v seems to be the best choice for me.

David
Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 11:21:02 AM
I will give that a go in the morning, looks like I'm getting close, now I just have to make the second tank! still cant stop thinking about that first gearbox,  I may have to try a very large gear on the end of it with a small gear for the nut (just cause I cant leave well enough alone :))

Phill

And a picture just incase anyone missed what the tanks are going into :)

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0051_zpsa6c00bb7.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0051_zpsa6c00bb7.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0054_zpsa755c830.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0054_zpsa755c830.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0050_zps67b96ae4.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0050_zps67b96ae4.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0052_zpsad671f3b.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0052_zpsad671f3b.jpg.html)
Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 11:28:01 AM
Hi Davy1, I think that's about it, I'm a fan of 12volt myself  but I'm thinking of mounting a 6v7ah gel cel in the pressure tank and a 12v drive battery in the free flood area, although I have wandered over into the darkside and experimented with Lipos lately, thinking one might be the go for the drive in one of those watertight boxes for mobile phones etc
When you mentioned a 4mm hole for your inlet/outlet, what size dia tank do you use?

Phill
Title: Re: Piston Tank advice
Post by: unbuiltnautilus on June 17, 2014, 12:32:11 PM
I will give that a go in the morning, looks like I'm getting close, now I just have to make the second tank! still cant stop thinking about that first gearbox,  I may have to try a very large gear on the end of it with a small gear for the nut (just cause I cant leave well enough alone :))

Phill

And a picture just incase anyone missed what the tanks are going into :)

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0051_zpsa6c00bb7.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0051_zpsa6c00bb7.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0054_zpsa755c830.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0054_zpsa755c830.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0050_zps67b96ae4.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0050_zps67b96ae4.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF0052_zpsad671f3b.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF0052_zpsad671f3b.jpg.html)

Very nice, we have more Typhoons than the Russian Navy on this forum!

Always loved the platypus tail :}
Title: Re: Piston Tank advice
Post by: mermod on June 17, 2014, 12:44:23 PM
Go big or go home  :-)) ;)

Beaver tails rule!

Phill
Title: Re: Piston Tank advice
Post by: Davy1 on June 17, 2014, 01:08:27 PM
Hi Phil,

I like that Beaver Tail too!

My largest piston tank is just over a pint (sorry it's the closest glass to hand!) but quite slow to fill and empty - about a minute. I find this OK. You may need larger than a 4mm ID outlet.

I have used 11v Lipos in my smaller subs for some years now with very good results. I put them in the WTC on the grounds that that way you get a better fire! Actually I've never had a problem with the Lipos. A recent flooding melted the Mosfet transistors in my proportional piston tank board but the Lipos (and the radio and the Microgyros ESC) were unscathed once dried out. Even the piston tank board worked after I'd replaced the full set of Mosfets.

I'm impressed by your gearboxes, by the way. I take the easy way out by using MFA motors with gearboxes.

David
Title: Re: Piston Tank advice
Post by: Subculture on June 17, 2014, 01:27:14 PM
Increase the inside diameter of the feed tube to at least 8mm or more. 4mm will slug the feed to your tank.

Also if possible make sure the spigot is at the top of tank endcap so it's easier to purge air.

I like the way Ron Perrott mounts his tanks- in the free flood section with the end of the cylinder fully exposed, can get any trapped air with that arrangement. Not so easy to do with a single tank though.
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: Subculture 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.
Title: Re: Piston Tank advice
Post by: mermod 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 :)
Title: Re: Piston Tank advice
Post by: Subculture 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.
Title: Re: Piston Tank advice
Post by: mermod 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.
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2108_zpsa29714e9.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2108_zpsa29714e9.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2109_zps4e78b4aa.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2109_zps4e78b4aa.jpg.html)
Title: Re: Piston Tank advice
Post by: mermod on June 22, 2014, 08:02:00 AM
a quick test fit of all the bits shows it needs just a little tweaking.
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2113_zps95b01626.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2113_zps95b01626.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2110_zpsefd8b704.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2110_zpsefd8b704.jpg.html)
Title: Re: Piston Tank advice
Post by: Subculture 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?
Title: Re: Piston Tank advice
Post by: mermod on June 22, 2014, 11:28:20 AM
Yeah, just in case any water gets past the plunger, just paranoid I guess.

Phill
Title: Re: Piston Tank advice
Post by: Subculture on June 22, 2014, 04:53:20 PM
Have you sealed the spindle too?
Title: Re: Piston Tank advice
Post by: profesorul on June 22, 2014, 07:29:03 PM
@ Subculture ,
 
Do You think is possible to do such thing ?.
 
MARIUS
Title: Re: Piston Tank advice
Post by: Subculture 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.
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: mermod on June 24, 2014, 12:26:38 PM
Nearly there :)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2115_zpse4194449.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2115_zpse4194449.jpg.html)

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2116_zps5286d591.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2116_zps5286d591.jpg.html)

Phill
Title: Re: Piston Tank advice
Post by: Davy1 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
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: Davy1 on June 26, 2014, 09:03:01 AM
Hi Phill,

That's great. Thanks for pointing it out.

David
Title: Re: Piston Tank advice
Post by: mermod 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,

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2149_zpsfe3f23f4.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2149_zpsfe3f23f4.jpg.html)

Phill
Title: Re: Piston Tank advice
Post by: mermod on June 26, 2014, 10:28:48 AM
And a shot of the insides with the aluminium hatch behind.

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2152_zps3ec20ef8.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2152_zps3ec20ef8.jpg.html)

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2153_zpsf5819212.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2153_zpsf5819212.jpg.html)

Phill
Title: Re: Piston Tank advice
Post by: derekwarner 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
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: Davy1 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
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: salmon on July 03, 2014, 02:49:11 PM
Phil, what happened to the pictures you posted?
Title: Re: Piston Tank advice
Post by: mermod 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
Title: Re: Piston Tank advice
Post by: salmon on July 04, 2014, 12:00:25 AM
Try Photobucket.com

Title: Re: Piston Tank advice
Post by: Davy1 on July 07, 2014, 03:07:43 PM


Quote
that murky water

It is murky water at Barrow but it is not that bad:

- It is quite wadeable and shallow (actually too shallow at the moment.)
- the pond is quite large (several hundred yards length and breadth) but an onboard "Pinger" limits the search area by a big factor. I've recovered my submarines many times over the years. (My fellow club members are threatening salvage rates!)

David

Title: Re: Piston Tank advice
Post by: mermod on July 08, 2014, 07:25:45 AM
Sorry about the blurriness but heres a shot of the tank so far with the end stops in place.

(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2172_zps43dfdb52.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2172_zps43dfdb52.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2173_zps753e268e.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2173_zps753e268e.jpg.html)
(http://i1357.photobucket.com/albums/q760/Phillip_Sachman/DSCF2174_zpsd6f69696.jpg) (http://s1357.photobucket.com/user/Phillip_Sachman/media/DSCF2174_zpsd6f69696.jpg.html)