Bouyancy Tank Idea

[geoffkx250]

I would like some opinions on an idea that I have. I would like to control bouyancy on my ROV. My idea is to use a section of 4 inch pvc pipe and I would inject co2 into using a solenoid valve. I would also release the air from the bouyancy tank using a solenoid valve. Water would escape and enter the tank through a small hole on the bottom of the tank.

Here is a drawing.

Thank you.

[soulreaper]

Looks good, and I'm sure you already thought of this but just in case you didnt, remember the balance of your rov will change as the CO2 tank empties (the tank will get lighter). Very nice idea.

[geoffkx250]

I was sure if I was re inventing the wheel with this idea - I am kind of new to this hobby. I am a certified diver so the idea of controling bouyancy in a similar manor poped into my head. The only potential design flaw that I see is - if the tank is partially filled with air there might be some instability. Think of an air bubble in a level. I countered this flaw with a new idea - what if I were able to counter balance with movable ballast. Using a simple stepper motor with threaded rod attached to weight inside of small diameter pvc, perhaps I could move ballast fore and aft? I dunno maybe I just like to think too much, lol.

One of the benefits of having compressed air or co2 on my ROV is the ablility to inflate a bag that I could attach to the top of the ROV which would allow me to hook and inflate in order to lift heavy objects (i.e. lobster pots)

In any case I appreciate your input and compliment on my design

[thegadgetguy]

Yes, I can definitly see the air moving, and I've had the same problem working on something else. I've seen one other ROV that used this design, and the guy got around that problem by useing four vertical tubes like yours. He put one on each corner, and filled them with equal amounts of air or water.
This is an interesting idea, I hope that you can get it to work.

[jason howard]

i had the same thought (im a diver too). in the end i decided for my first rov i would go with the simplest set up i could make. the adjustable bouyency system eliminates the need to make the rov nutraly bouyent but you still need to balance the teather. plus if you run two tanks, thats four solanoides and two supply tanks plus the tubing and fittings of added weight. plus you need to add the solanoids wiring into the teather and control system. in the end the adjustable system has multipal possable points of falure, but is entirely possable. i plan on implmenting that very system on my next rov. ps you could try using a baffel system in the tanks to slow any water movement down, drill holes in the very bottom and top of the baffels but not to big that way water and air can move but not fast, use some perminant flotation on the outside just for pitch and roll stablization and add some weight so you acheve negative bouyency before 3/4 blow. that way you have enough air to remain stable. if you set it up like this you double down on falure protection.

[jason howard]

and i would recommend using air not co2. co2 has different expansion rates depending on temp and pressure, and because it becomes a liquid during compression it has to phase change back to gas during decompression witch can result in inconsistant amounts of gas released per release and post expansion even if you put an expansion chamber inline. just ask anyone who has played paintball witch is more consistant and reliable. they will most likely say compressed air. its lighter as a complete system and dosent require an expansion chamber, just a regulator. also i would suggest putting in an overpressure valve so if there is a pressure problem your valves dont break or worse tanks explode. tanks arent to crazy expensive and can be found on ebay for a deal or at a local paintball place for an arm and a leg . if your a diver you can use your main dive tank to fill the ballest supply tank so you dont have to go to a co2 fill station after every run.

my 2cents

[Kjetil]

Is it possible to just compress the air in the tank with water?

I was thinking about have one pump that can pump both ways.

Use 4" pipe as tank, pump in water in the low side of the pipe (tank) to get the ROV down and pump/ bleed of water to get the ROV up again.

Have any tried this solution?

[Seadragon]

that is how basically a submarine surfaces and dives. I can see you using an airbrush compressor but you would have to have float valves for the water level shutoff. on a submarine they surface and as soon as they have air flow from outside they charge up the internal air tanks.

[Kjetil]

I did a test yesterday. I used a windscreen washer pump. This is capable to pump up to 2 bar (29 PSI).

Pumped water inn to a plastic bottle. Was able to pump in 0,9 liter of water in to a 1,5 liter bottle.

The problem is that the air pressure is pushing the water out of the bottle and througt the pump when the pump is not running.

Is the any small pumps that is reversable and will not let pressure throught when its stopped?

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[Silver dollar]

You can always use a check valve to prevent the water to go backwards