Has anyone ever tried to use a SCUBA tank or a "spare-air" tank for pressure normalization? In theory, you could attach the SCUBA mouth-piece to the air compartment of the ROV which contains the electronics/camera/etc and also attach some kind of purve valve on that compartment that automatically purges when the pressure inside surpasses the outside pressure. As the air from the tank is used, however, the buoyancy from your ROV would increase, as the air in the tank becomes less dense.
To take it even further (may be adding too many moving parts here), you could use the air from the SCUBA tank for buoyancy control, somehow.
As long as the tank and the ROV don't change size, and the air is not leaking out, the two together should maintain the same buoyancy. There has been no change in the amount of displaced water or the total mass. Another way to think of it is that as the density of the air in the tank decreases, the density of the air in the ROV increases and balances out. During accent, you would probably have to vent the added gas from the ROV. This would lower the total mass and the ROV would weight less overall. So, if you were neutrally buoyant at the start, you would be positively buoyant after accent. The air in the tank could be used for buoyancy control, but the air would have to go into something that either inflates or pushes out water from an open tank. Both great ideas. I also worry that this would go beyond the simplicity threshold for the project. A clever solution would be wonderful though.
The idea is sound; however, I think the thought process is a bit "heavy" :) If you look at some of the model sub's that you can play with. Sorry, I don't have any URL's right now but Google finds them. They are using ballast tanks and compressed CO2 to push water out of the ballast tanks. Using some of the same hardware and adapting it to the ROV would get you close to the "mini-scuba" gear you would need since the ROV is small compared to a scuba tank.
Hi everyone, I know a fella that built a pressure normalized pvc unit using a barbeque regulator (has a very small differential) coupled to an aviators oxygen bottle (filled with nitrogen and may have had its own higher pressure regulator) and a simple spring loaded relief valve for ascent unloading, kind of a purpose built one shot unit he used to put a rope on a sunken airplane in order to retrieve it. Thought the idea was brilliant even for shallower dives as all those issues with shaft seals, wire exits and such are sure minimized, now if a guy could make the stored air pressure do other fantasic things like bouyancy / ballast control / manipulator arm drive etc then it would sure be a nice feature and more worthwhile incorporating. Is someone able to share the formula for calculating the max depths given a pressure tank of a given volume at a given pressure used to pressurize a hull chamber of a given volume. That math part should be pretty straight forward eh?