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Apr 12, 2021, 08:09 AM
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Question

Motor and gearbox for mini piston tank.


Saw this ad for a motor/ gearbox with a long output shaft that can be used on a mini piston tank ( syringe).

My question is, which variant should I get?
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Apr 12, 2021, 03:12 PM
Registered User
The right part is the one designed for the needs of your application. Critical information is missing.

How much load torsion is measured under full load? Until you answer that, you are reduced to guessing, and that can be expensive. A force gauge or equivalent is needed to select the most compatible part.
Apr 12, 2021, 08:45 PM
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microgyros's Avatar
I assume this is for the VII where top displacement is around 70cc and styrene relative to water density is ~1.03.
Further assuming 100ml in syringe volume.

In SI units:-
Force = pressure * area
Energy or Work done (joules) = force * distance
= pressure * area * distance
= pressure * volume
Power (watt) = pressure * volume /second

at 5metre depth the pressure is 50kPa or written 50x10 Pa
10cc per second is 0.01 litres⁻ or 10⁻⁶ ms⁻

Lossless or ideal piston power to shift 10cc per second at 5metre depth is
Power (watt) = 50x10 * 10⁻⁶ ms⁻ = 50x 10⁻ , which is slightly greater than nothing at all.

The efficiency of the tiny motor is a flattened peak but around 0.4 in absolute terms through it's operating range.
You are left to find seal friction and gearing loss.
Could a syringe friction be measured by weight?
Anyway, that part is not in my domain but it seems to me to be more than ten times the nothing value of compression.
The data sheet specifies rotational torque in both working and stall terms in kgcm , In SI units of Newton metres, 2.2 kgcm is 0.0982 * 2.2 or 0.216 Nm
M4 thread pitch gives you a pushing force.

In short, my answer is,
  • pressure is insignificant compared to estimated friction
  • the low ratio is adequate for > 90% friction force,
  • the high gear ratio is too slow
  • look to youtube for practical demo and to ask who you know has built these and done this before. (Andy)
Apr 12, 2021, 09:32 PM
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Thread OP
Hi Andy,
Thanks for the info. The gearbox is not meant for the Type VII or any particular sub at the present. Just saw it at an online shopping site. I've seen some RC hobbyist use similar items for syringe based piston tanks onboard small RC subs like Revell's 1/144 Type 212/214 kits. I was thinking of getting a couple just to tinker around with. Just don't know which particular one to get.

I've tried getting in touch with the builders. Unfortunately one of the builder posted that he doesn't know the specs of the specific gearbox he used. I'm still trying to get in touch with another builder.
Apr 13, 2021, 02:31 AM
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microgyros's Avatar
You should know me after nearly 12 years. (okay, whom you know has built!)
I meant Andy as the one who has made the mechanisms from 400ml hdpe cartridges and medical syringes.


I think the youtuber piston fellow, whose channel you have linked to, is very clever and I like that channel very much. I doubt if all the effort is intended solely to perfect 1/144 scale models. They are on the small side for the added complication.

I made the slightly largerTrumpeter Kilo as a dynamic diver with a low freeboard. I wouldn't consider converting it to a static ballast tank and will only try for kicks as I figured my own way to do small scale static ballast control.
I found more old photos of older wtcs and will fire one off to you in a moment.
Apr 13, 2021, 07:22 AM
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Ooops. Sorry Mike.

Was going over some mini piston tanks videos on YT. I found this,
Syringe Piston Ballast Motor Replacement (from RPM50 to RPM300) (2 min 36 sec)


3v 200- 300 rpm
Last edited by redboat219; Apr 13, 2021 at 07:32 AM.
Apr 13, 2021, 08:10 AM
Man from Atlantis
Sub culture's Avatar
Any one of those motors will be sufficient to drive a piston tank with a modestly sized piston say 25-30mm diameter. The seal friction is insignificant compared with the force acting on the piston as the air compresses behind it, or if it needs to be emptied at depth.

You just have to decide on the filling/emptying speed you're looking for.

There's a whole chapter devoted to piston tank design in Norbert Bruggens book Model Submarine Technology, with some pretty straightforward formulae that make it a snap to select the right motor and gear ratio for a desired size of tank.
Apr 13, 2021, 09:39 AM
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Quote:
Originally Posted by Sub culture
Any one of those motors will be sufficient to drive a piston tank with a modestly sized piston say 25-30mm diameter. The seal friction is insignificant compared with the force acting on the piston as the air compresses behind it, or if it needs to be emptied at depth.

You just have to decide on the filling/emptying speed you're looking for.

There's a whole chapter devoted to piston tank design in Norbert Bruggens book Model Submarine Technology, with some pretty straightforward formulae that make it a snap to select the right motor and gear ratio for a desired size of tank.
Time to pull out the book.
Apr 13, 2021, 06:18 PM
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microgyros's Avatar
Quote:
Originally Posted by redboat219
Time to pull out the book.
I think if you consider an respond to the point from CC Clarke and you may find the apparant contradiction between my speculation and Andy's answer isn't there any more. A 400mm silicone cartridge within a confined wtc isn't what I'm visualising from your recent posts and the diagram of a vented system you sent to me last year.
Whichever you use, you already have the suggestion to measure friction with weights and you can calculate force, but don't forget to work in SI units of square metres, Nm and not ml, cm, kg, litres etc.
Jun 05, 2021, 06:04 AM
Latitudes vs Attitudes
Bob Gaito's Avatar
Quote:
Originally Posted by redboat219
Ooops. Sorry Mike.

Was going over some mini piston tanks videos on YT. I found this, https://youtu.be/X8fxC-XgqHs

3v 200- 300 rpm
Where does the air go? presently its going out past the motor's gear threads necessitating the whole thing to be in a sealed container(dry hull) and at that point it will probably bypass the piston's gear and just transfer to the other side of the piston as it travels? am I seeing this wrong?

Syringe Piston Ballast Motor Replacement (from RPM50 to RPM300) (2 min 36 sec)
Jun 14, 2021, 05:17 PM
Registered User
Your guess is correct - the air goes into the enclosure around the piston tank, like the WTC or some sealed compartment.


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