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Author Topic: Piston Tank advice  (Read 13429 times)

vnkiwi

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Re: Piston Tank advice
« Reply #25 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
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Subculture

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Re: Piston Tank advice
« Reply #26 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.

mermod

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Re: Piston Tank advice
« Reply #27 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
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Re: Piston Tank advice
« Reply #28 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.

mermod

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Re: Piston Tank advice
« Reply #29 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
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Re: Piston Tank advice
« Reply #30 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.

mermod

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Re: Piston Tank advice
« Reply #31 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
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Re: Piston Tank advice
« Reply #32 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.

mermod

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Re: Piston Tank advice
« Reply #33 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
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Re: Piston Tank advice
« Reply #34 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.

mermod

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Re: Piston Tank advice
« Reply #35 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
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mermod

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Re: Piston Tank advice
« Reply #36 on: June 17, 2014, 04:51:32 AM »

Nearly forgot the picture.
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Davy1

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Re: Piston Tank advice
« Reply #37 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
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Re: Piston Tank advice
« Reply #38 on: June 17, 2014, 10:01:35 AM »

15.23:1 by my reckoning, so unloaded spindle speed should be about 850 rpm.

mermod

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Re: Piston Tank advice
« Reply #39 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
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Re: Piston Tank advice
« Reply #40 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.

mermod

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Re: Piston Tank advice
« Reply #41 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
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Re: Piston Tank advice
« Reply #42 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.

Davy1

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Re: Piston Tank advice
« Reply #43 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
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mermod

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Re: Piston Tank advice
« Reply #44 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 :)




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mermod

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Re: Piston Tank advice
« Reply #45 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
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unbuiltnautilus

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Re: Piston Tank advice
« Reply #46 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 :)






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

Always loved the platypus tail :}
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mermod

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Re: Piston Tank advice
« Reply #47 on: June 17, 2014, 12:44:23 PM »

Go big or go home  :-)) ;)

Beaver tails rule!

Phill
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Davy1

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Re: Piston Tank advice
« Reply #48 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
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Re: Piston Tank advice
« Reply #49 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.
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