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Postby aquadeep » Sat Apr 04, 2009 11:05 pm

Yes with tanks that are non pressurized exact control is done much the same way as a piston tank .I use both sysytems on 2 subs but found the first type to be simpler and cost less ,no aftermarket module needed nor have to depend on the maker to continue making them.I am sure one could just make there own.Also friction in the piston seals cause some degree of extra exsertion or pressure increse in both directions of travel making it less effecient to operate.

But why if the same thing can be done for less all around hassles?

Im not saying mine is better its just cheaper and anyone with basic skills can build it ,no special electronics to operate,no guessing.

By the way do you have depth telemetry on your sub,it senses almost to the mm. 8)


I thought you make your own piston tank ,hence the lathe ,my mistake. :)

Dave :D
Last edited by aquadeep on Mon Apr 06, 2009 9:19 am, edited 1 time in total.
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Postby JWLaRue » Sat Apr 04, 2009 11:17 pm

aquadeep wrote:Yes with tanks that are non pressurized exact control is done much the same way as a piston tank .


You'll need to explain how that is done as I do not see how it can be the same. Aren't you using some sort of solenoid valve or pump...which is not providing any sort of repeatable metering of the air/water flow. What is the method of "exact control"?

With the piston, I am using a Hall-effect sensor that counts the number of revolutions of the main drive gear that moves the jack screw. The main gear has a pair of magnets glued to it. The electronics module keeps track of exactly where the jack screw is based on the revolution count. A given position on the slider is always the exact same position on the piston.

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Postby aquadeep » Sat Apr 04, 2009 11:41 pm

The water is simply pumped in and air escapes out of the sub,iether a solinoid valve or pinch tube valve via a servo ,2 one way aquarium or CO2 valves take care of the air and water flow automaticly this is used on the big subs or just the mini gear pump on smaller subs where leak threw the pump is not an issue,the tolerances are greater..

The exact repeatabilty is done in just watching the depth readout,or observe the sub,when the numbers are repeated your there and turn off the pump,just like full size subs do ,I believe.

The piston system is very good ,the Eropeans have done it for a long time but cost more to reproduce on multiple subs.

What happens if there is a flood,can the module still work?

Dave
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Postby Albion » Sun Apr 05, 2009 12:14 am

So repeatability is only good because you now have the telemetry! which couls be applied to pistons, some of which have on board depth controls.

There is nothing to stop a piston unit being applied to multiple subs, wheller dealer has a WTC with pistons, and i have a module which can go into multiple dry hull boats or into a WTC.
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Postby Sub culture » Sun Apr 05, 2009 6:04 am

The advantage of a piston based system, and really this advantage is in the last 10% of positive buoyancy, is it can be fitted with some form of proportional feedback. This can take a form of a magnetic encoder or a potentiometer, but the principle remains the same- you can measure accurately the amount of water taken onboard.

This means once you set-up your trim, you can repeat this as often as you like with just the throw of a switch. You can get the best of all worlds by combining a piston tank trim cell with a compressed air or pumped water ballast system for boats that have high freeboard.

Unfortunately, piston tanks are difficult to make without access to a lathe. The commercial versions are, understandably, a tad on the expensive side.

Chiefly the spindle nut and piston is the most difficult to construct sans lathe. However if your lucky enough to have a lathe, or can persuade a fellow modelmaker to knock up a few pieces for you, a piston tank can be put together very cheaply indeed.

BTW, it often amazes me how many modelmakers bulk at the cost of purchasing tools, but are quite happy to drop large amounts of money on kits.

A lathe and bench drill will soon pay for themselves when you can make your own endcaps, cylinders, shaft seals, piston tanks etc.
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Postby raalst » Sun Apr 05, 2009 7:37 am

Unfortunately, piston tanks are difficult to make without access to a lathe.


hang in there, I have written an SCR article about creating your own piston "tankette"
with a syringe, a servo, a hand-held threading tool and a bit of courage.

it's not a 100% replacement of an Engel tank of course but combined with
a fixed full/empty-mode MBT it could help you out nicely.
For small models this approach is usable as MBT.
I ran this setup in my Trumpeter Kilo for three years.

Now start hunting for the biggest syringe you can find.
one gram of buoyancy is about one milliliter (cubic centimeter) of water.
I found syringes up to about 30 milliliter. tips : horse vets, paint shops, shops selling poyester & epoxy.
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Ronald van Aalst

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Postby Sub culture » Sun Apr 05, 2009 10:34 am

60ml are easily found, 100ml are available but much more difficult to find.

A very good source of tubing for medium sized tanks is silicone caulking refills. It's got a very accurate internal moulding. You would still have to make a spindle and piston though.
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Postby JWLaRue » Sun Apr 05, 2009 3:53 pm

So.....all this just confirms my original statement that only a piston-based system can be controlled with absolute repeatability. Anything relying on eyeballing the state of the sub, whether by looking at "telemetry" or simply the trim condition of the sub is just not the same.

But let's not lose sight of the variety that we have in this hobby. That's part of what makes it so interesting (at least to me). I have yet to build a sub model that uses the same ballast system more than once. Leveraging their trade-offs is a good part of what keeps me building more (and more!) sub models.

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Postby Sub culture » Mon Apr 06, 2009 2:17 am

I had considered the possibility of fitting a pressure sensor to a sealed tank water pump ballast system. The sensor could be rigged to sense the compressed air in the tank, feeding back to a small micro controller, this could shut off when it reaches a certain pressure (dictated by the operator on the bank) thus giving a form of proportional feedback.

How the sensor might be affected by water/air temperature was a point I considered, there is also the linearity of such a sensor to consider. Sloshing is another concern, although that could be largely dealt with by fitting baffles, which this kind of system should have anyway. A variation on this could be a small trim tank with a perisaltic pump.

The latter could be a sealed tank with the pressure transducer, or a small syringe. If using a syringe the pressure sensor could be dispensed with, and a piston tank control board fitted with feedback of the piston position.
Not sure if the controllers would have enough deadband to deal with any overshoot of this system, but it's an area ripe for experimentaion.

Such a system could be put together without any machine tools, just basic bench work.
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Postby aquadeep » Mon Apr 06, 2009 9:12 am

As Subculture mentioned and I agree ,the piston system cost more and more than likely requires the use of a laithe.

Of coarse there is nothing stopping piston tanks from going into multiple subs ,just how much money you want to spend,it can get pricy on all the deferent sizes,electronics ect. necessary to install in variuse sizes of subs.

As I said before It is a very good and acurate system,I illiminated the jack screw and went with just the piston tank and gear pump nothing else.

Still the CG changes that is inevetable unless there mounted vertacly and then its even better.Yet I wounder why full size subs dont employ them,at least none that I have seen?

Getting back to what this thread is about in the first place,if your a novice builder the Engel pumps are good but be prepared to spend sum bucks!
In my opinion even if your a novice still do your best and build your own system as I have for years ,its much more rewarding and cheaper .

In todays economy the added great expense of both the kit and the laithe would be prohivative to the avrage builder and to learn the necessary skills to pull it of.. :shock:
Personaly I have invested in kits rather than expensive tools that would see very little use,if I need machine work I would farm it out to a profetional ,but so far have not seen the need. :roll:

The telemetry system is the ticket for any body wanting to know whats going on with there sub both on the inside as well as out and can be very helpfull in measuring the piston travel,water levels ect.A huge variaty of sensors can be employed or made to suit the hobby. :D :D
If you cant see your sub at least you will know what its doing!
I wont leave port without it.

I bet the 2 Captains above would enjoy the benefits of the system and explore all of its potential not to mention aiding in sub safty.

Now we can employ digital and analog telemetry like reaserchers ect. do.

Dave :D
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Postby aquadeep » Mon Apr 06, 2009 9:18 am

Here is a realy big piston pump ,perhaps a good candidate for use in larger subs.
Image
Its a manual fliud transfer pump available at most automotive parts stores.

Dave
"I like submarine comanders ,they don't have time for bull!!" and
"Don't tell me it can't be done!"

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Postby Sub culture » Mon Apr 06, 2009 10:41 am

I never said the piston tank system was expensive, i said the commercial piston tanks are expensive. They're produced in low volume, specifically for the model submarine community, which is tiny when compared with a high volume product like a windscreen washer pump.

If you have the tools and the know how, a piston tank system can be built for about the same amount as a waterpump system.
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Postby aquadeep » Mon Apr 06, 2009 2:03 pm

I build the non pressurized system for about 25 bucks,no expensive tools.

Then again IF you have the tools and an alot of money the sky is the limit.

Dave :D
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Postby JWLaRue » Mon Apr 06, 2009 3:51 pm

aquadeep wrote:Still the CG changes that is inevetable unless there mounted vertacly and then its even better.

I bet the 2 Captains above would enjoy the benefits of the system and explore all of its potential not to mention aiding in sub safty.


No. That's why most Engel-based systems use two pistons.

And to be perfectly honest the telemetry gadget doesn't hold any interest for me at this time. I'm currently more interested in pursuing operating 'scopes and torpedoes and such.

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Postby Pirate » Tue Apr 07, 2009 8:28 pm

Why is it every time someone asks a question about ballast systems there is a turf war?

I guess everyone has their favorite.

If it works, it's a good system. I've found that getting any of them to work properly is a challenge.

So i just jump in the water and push my sub underwater and Brrrrrrr my lips against the water for sound affects. Then when I want to surface I yell, "Surface! Surface!" and lift it to the surface. For some reason I get a bunch of funny looks though. I guess people aren't used to seeing an operational R/C sub or something.

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