I'm new! ROV ideas

[willlgord]

I used Windows paint to make the drawing....it's really simple to use once you learn a few tricks.

I agree oil would be better (especially at extreme depths) but I'm not going that deep and I don't want to deal with the mess. I don't think the displacement/bouyancy will change much from using air unless you consider the extra weight of compressed air over uncompressed air. The pressure inside the ROV will be equal to the surrounding water so there will be no flex or expansion of the structure.

[Stoic]

FYI for everyone, compressing air does not change its displacement. Volume is the only consideration when calculating displacement. SCUBA divers would be hosed if that were not true.

[willlgord]

I know that the weight of compressed air is heavier than uncompressed air (ever so slightly at the pressures I'll be using) which does change the buoyancy of the ROV (again, ever so slightly).

I found this :

Air has an average molecular weight of 29 (28 for N2*.8 + 32 for O2 * .2)
1 mole of gas at STP occupies a volume of 22.4 L, therefore, 29g {~1 oz)of air at STP occupies 22.4 L

Take you tank volume in Liters (ft3X28.3 or cu in X .0164) and correct to STP (forget the temperature, just multiply the volume by 204 or 306{3000psi/14.7psi; 4500/14.7psi}. This gives you the gas volume at STP.

Divide this volume by 22.4 and you get the weight of air in oz.

Using that, you get the following information:

3000 PSI = 204 atm
4500 PSI = 306 atm

47ci = 0.77 L
68ci = 1.11 L
88ci = 1.44 L
114ci = 1.87 L

So now, just plug it into what I said above, and you get these weights:

47ci 3000PSI tank: 7.0 ounces of air
68ci 3000PSI tank: 10.1 ounces of air
88ci 3000PSI tank: 13.1 ounces of air
114ci 3000PSI tank: 17.0 ounces of air

47ci 4500PSI tank: 10.5 ounces of air
68ci 4500PSI tank: 15.1 ounces of air
88ci 4500PSI tank: 19.7 ounces of air
114ci 4500PSI tank: 25.5 ounces of air

As you can see, the weight of compressed air is not negligible, especially in higher pressure setups.