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New hypothesis ballast system - Comments appreciated

R/C Submarine modelers

Postby Skip Asay » Wed Nov 12, 2003 5:11 pm

Carl -

Thank you for the heads up. I stand corrected.

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Postby Slats » Wed Nov 12, 2003 7:35 pm

To all those people who have contributed - many many thanks.
These comments are great and have given me loads to think about. Thanks so much for your efforts.

Skip,
you stated:
"Contrary to popular opinion, a pump type ballast system does not mean that you’re limited to periscope depth operation only. I’d like a nickel for every time I’ve heard “how do you surface if the air intake is below the surface?” The answer is very simple - drive the boat back up until the intake is out of water. With a fully flooded ballast tank, I can drive Albacore and Marlin to decks awash easily. And that’s using just the bow planes."

However, please note that the very first sub I built used this prinicple, and it bottomed out in an Olympic Swimming pool due to a tiny leak in the WTC. When the boat was retrieved the leak let in just 30ml of water. The boat was ballasted so a fully ballast tank meant the boat was at decks awash yet this extra 30 ml of water held the boat on the bottom. The batteries were fully charged and with plenty of power and full servo control, the boat was pinned on the bottom. I.e I simply could not drive up to snorkel depth. So unless you rig up a hybrid system a pump ballasted boat with a vented ballast tank is (I believe) -not a safe way to go.

Skip, you stated also
"While a positive displacement pump will create some vacuum in the tank against a closed intake (snorkel), just how much remains to be seen. I’d think that the pump would need a substantial amount of power to be able to remove enough water to reach the “30%” mark. But the real problem here is that any significant vacuum in the ballast tank would hold the snorkel valve (ping pong ball?) closed with enough force that gravity alone won’t be able to allow the float to drop. Some form of mechanical actuation would be required (servo and another channel) and this destroys the K.I.S.S Principle."
Thanks for this Skip, -this is where my thinking is right now. I am doing some testing next weeked or so and would be happy to share the results.

By the way Skip, the shippment you sent me on 21 October has still not arrived. Did you send this by air?
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Postby Art Broder » Wed Nov 12, 2003 11:07 pm

Slats,
This discussion mentions comparisons of available ballast systems.
As you might know, I use a different ballast system in my 1/72 L.A. and Alfa. The following URL has a video of my Alfa, utilizing the Recirculating Compressed Air Ballast System. You might have to join my MSN Group to view the video, if you can access it:Art Broder's Models . There is no automatic depth controller on this model. It can be brought up from the bottom even if your prop is stopped by weeds, or if your ESC has blown a fuse. The 6 or 12V system uses an air pump, not a water pump, and is simple and effective. Go to www.groups.msn.com/ArtBrodersmodels , if the above link does not work, and click on Documents, in the left column, click on the ballast system and read the 32K doc. file. and then view the pictures. Hope this stimulates more discussion.
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Postby KOEZE » Thu Nov 13, 2003 8:49 am

@Skip,

You do realize I hope that with a rigid ballast tank and and a few ml of air bubbles left in a tank you would have to draw an alomst absolute vacuum to draw more than a more water out that there is air.
Suppose the pressure inside the tank is 1 bar. The sub is near the surface and wants to pump out the tank. There is 20ml of air in the tank. In order to get that 20ml to expand to 40ml you have to have half the pressure ie. 0,5 bars. That is a LOT of vacuum allready and that only enables you to pump out 20ml of water. That is near nothing. A medium sized seringe holds 20ml.
If however the tank is flexible than not only the little pocket of air in the tank can expand but the entire volume of the submarine can expand. This requires MUCH less vacuum and can be done.
I however cannot see a waterpump (gear of piston) pump more than a couple of 10th of bars vacuum resulting in maybe a couple of ml of water being pumped out.

My idea of safe pump operated submarines is:
- Flexible tank.
Can allways be emptied even if there is no air in the tank
- CO2 capsule
To empty the tank even is there is no power to the pump or the water inlet is blocked.
- Dropable ballast weight to increase bouyancy


I have to say. I do like the idea of the needle valve with float for the Schnorkel.
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Postby Skip Asay » Thu Nov 13, 2003 9:58 am

Koeze -

In referring to "vacuum" holding the snorkel closed, I should have said "pressure differential". This would be the case with a ballast tank that has absolutely no air inside. If there is an air bubble, then "vacuum" would be appropriate and some water would, in fact, be removed from the tank, although not very much. The amount of pressure differential would still be the same and the snorkel float would still be kept closed, even though it's above the surface. This is wanted I wanted to explain.

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Postby safrole » Thu Nov 13, 2003 11:16 am

KD6HQ was kind enough to do a better job than I depicting the "carburetor float" style of seal. He points out that the float would need to have a bit of weight to break the vacuum when the boat surfaces.


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Postby KOEZE » Thu Nov 13, 2003 11:53 am

@Skip,

Point taken.

What I was referring to is this quote

“Surfacing - when fully dived at depth beyond the reach of the snorkel, the snorkel vent remains closed. To surface the 6 v geared pump runs in reverse and starts pumping out water. In doing so a vacuum forms in the ballast tank as its not vented, but the geared pump can overcome this. When the ballast tank has only pumped out 30% of the water, the boat is or should be close to decks awash, and the moment the sail breaks the surface the snorkel valve opens automatically, the vacuum is then released and the pump then empties the full contents of the tank.”

I have very serious doubts that any (usable) pump can pump out more than a few ml. I thought you meant that a geared pump should be able to pump out +/- 30% of the volume of the tank.

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Postby Ramius-II » Thu Nov 13, 2003 6:29 pm

I disagree that you get a smaller battery. The issue isn't current draw, it's power consumption.

P=I*V (power=current*volts)

For motors with similar power consumption, a 12V motor will consume half the current. This is true. But overall power consumption is roughly equivalent.

So lets say for a 6V pump motor you need a 6V 2AH gell cell, but a 12V pump motor would let you use a 12V 1AH gell cell. This is not a smaller battery. Both batteries output about the same amount of power, and so they are roughly equivalent in size.

Here's an example:

Power-Sonic 6V 2.8Ah 2.60" X 1.30" X 3.86" 1.25 lbs
Power-Sonic 12V 1.2Ah 3.82" X 1.65" X 2.00" 1.3 lbs

In this case, the 12V battery weighs about the same as the 6V battery, even though it's less than half the AH rating. (This is due to slightly higher weight efficiency of the 6V battery).


A little clarification:
Back on July 7 of this year there was a discussion on motor theory. RAALST explained the factors very well. Basically, while it is true P=E*I, you first must determine I (current). Two 500 series motors with the same power (torque and RPM) one a 6 volts draws 3.5A the second a 12 volt motor draws 0.8A. This all has to do with the size of the wire used to construct the motor, number of poles and the motors internal resistance when turning. 12v motors are more efficient. If this were not true, then commercial building would use 110v motors and not 480v motors. Subway system could use 100vdc rather than 600vdc.Thus the I squared R formula is the most correct.
As for battery size, take the height times the width times the depth and the 12v battery is slightly smaller at 12.6 ci vs 13 ci. ???
I would like for slats to be successful in his project and my input was intended to provide him every advantage. Sorry for starting a motor theory debut.

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Postby Slats » Thu Nov 13, 2003 9:59 pm

Gee - you guys are terrific.
This is what I love about remote control subs - pooling of heads together, frequent but constructive disagreement, -this what I think is the attraction to subs is that skimmer skippers don't or cannot understand.
Thanks again a whole bunch.
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All the best
Slats :D
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Postby kd6hq » Tue Nov 18, 2003 1:39 pm

Hi Slats

I know that this is off topic but do you have any close up pictures you could send me of you Alfa?

thanks

Don
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