Static ballast tanks

[Dace]

I'm kicking around using static ballast tanks. Using water as ballast to dive and to surface using a pressurized gas which will force water out of the tanks. I'll use 3 valves controlled by a microprocessor. One valve will be a vent valve mounted at the top of the tank. the other two will be mounted at the bottom. Lets call them valves A (vent), B (inlet) and C (gas valve). When I want to surface (tanks being empty at this point). I send a command to valve A to open and at the same time valve B opens to allow water in (valve A is venting). When I have reached the depth I want, both A and B close. To surface I send a command to the vent valve A at the same time the gas valve C opens allowing propel (gas) Into the tank and forcing water out of the vent valve. Air displaces the water and the ROV begins to surface. The gas will be regulated, I'm thinking between 1-2 PSI. I have to hammer out the details on depth, outside pressure, yada yada yada and also a depth meter. I appreciate any and all advise, criticism's or just plain crazy looks.

Dace

[Silver dollar]

IF you decide to go for this solution, I suggest to put in baffles in the tanks. This to avoid open water surface in the tanks. When you start to move the ROV forward the water in the tank will move aft. And when you stop the ROV the water will move forward. It can be a resonace and the ROV will be very hard to manouver.

[rossrov]

viewtopic.php?f=13&t=1156#p6077

[kenl]

The RC Sub guys have some pretty advanced ballast ideas, I don't know how deep they dive but the piston tanks they use seem to be pretty simple, just not sure where on my yet to built ROV I would put one and not unbalance it.

There are some options on this site http://rc-sub-workshop.com/. I couldn't get the site load properly when I checked it a minute ago, so hopefully the link is still good?

[Oldsirhippy]

I read in one of the RC submarine groups that the max dive depth for the submarines is 8 feet or so, if deeper the RC loses effectiveness.
Most ROVs go deeper and do not use RC.

[Dace]

thanks for the replys.

RossROV, I had thought about something similar to your idea but I found it a little to complicated. The simplest design using the KISS rule would be 3 valves and a can of propel.

Silver Dollar, good idea. I hadn't thought of that and it makes sense. I plan on using 3" schedule 40 PVC pipe for the ballast tanks. Maybe cutting half radius circles out of plexiglass and drilling 1/4 holes for water to pass through?

Hippy, I really had not thought about how deep I want to go but I think for my first ROV, 50 ft would be a good starting depth. Again I'm just hammering out the why's and wherefore to's.

Thanks for the input guy's
Dace

[Oldsirhippy]

At 50 ft the pressure according to http://www.calctool.org/CALC/other/games/depth_press is about 37psi, so I assume you will need air at > 37psi to shift the water out of the ballast?

[Dace]

At 50 ft the pressure according to http://www.calctool.org/CALC/other/games/depth_press is about 37psi, so I assume you will need air at > 37psi to shift the water out of the ballast?

Yeah, I didn't think of that. The outside pressure, if greater than the pressure in the tank will pretty much negate the force from the propel. If I increased the size of the pressure tank I will have to increase the size of my ROV to accommodate the bigger tank. I wanted to keep the ROV small enough to strap onto my kayak so I could film some epic striper battles from a different perspective, and check out some wrecks we have off the cape. I'll have to re-think that. I like the idea of a static ballast and don't want to abandon it. I'll research some tank sizes and pressure capacities. Maybe a bladder type system housed in a open ended tank? It would be easier to displace the water than to force it out of an opening.

Thanks Hippy

Dace

Oh and happy Thanks giving!

[a_shorething]

<snip> Maybe a bladder type system housed in a open ended tank? It would be easier to displace the water than to force it out of an opening.

Dace,
I don't think there's a difference between displacing water and forcing it out of an opening. You need to displace it with something and that something has to overcome the pressure of the water at depth. The hard numbers are the 37psi and the amount of it you need to displace in order to achieve positive buoyancy at that depth. The good news is it may not take much volume to get from neutral to positively buoyant and the tank doesn't have to be large. I'm not sure what pressure those little paint ball canisters hold CO2 at, but if it's more than 37 psi you could use one of them.

[SSN626B]

@Dace,
You might want to consider using a model aircraft landing gear air powered retract system. I have such a system without the retracts and the air canister is of reasonable size and can be pressurized to 100 psi. The servo controlled air valves were included with the air tank.
Also, you can try here: http://www.mikessubworks.com/page1.html and look under the Basic Ballast Systems.

@Oldsirhippy
I was always under the impression that the pressure on a hull increased ~14.7 psi for every 33 feet of depth. Therefore the pressure at 50 ft should be around 22 psi?

Regards,
TCIII/SSN626B