Tether buoyancy idea.

Waterproof Housing, Frames, and Buoyancy Methods.
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PaulC
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Joined: Nov 13th, 2010, 9:19 am

Tether buoyancy idea.

Post by PaulC »

Had an idea the other day, and had posted it on another rov forum with not many people getting on board with the idea. Anyway, has anyone tried using little capsules made of PVC to add to a tether for buoyancy? I have discovered that a lot of people who are using foam along the tether to make it neutrally buoyant complain that the foam gets compressed at depth and doesn't work as well... so why not make little capsules made of PVC say two to three inches of 3/4 inch PVC with a cap at both ends (sealed of course,) and put that along the tether. First thoughts are one it won't compress, two it will not get waterlogged, and finally it can be reused on other ROV's if you decide to make a new one.
Carlos D
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Joined: Nov 13th, 2010, 12:21 pm
Location: Palmetto, Florida

Re: Tether buoyancy idea.

Post by Carlos D »

The only thing I could think of are the gas laws, I think it's Boyle's Law that states that
volume is inversely proportional to pressure. So as external pressure increases, the
internal volume of the air contained in the capsules will decrease as well. I dive and
it's what happens to the air in my BC. I'm by no means an expert but thats what this
forum is all about, exchanging ideas. Good luck with your project and let us know
how it worked.
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PaulC
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Joined: Nov 13th, 2010, 9:19 am

Re: Tether buoyancy idea.

Post by PaulC »

Thanks for the reminder about Boyle's Law, but it just seems that at least I wouldn't have to deal with an as soggy tether. LOL.
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Pilikia
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Re: Tether buoyancy idea.

Post by Pilikia »

I believe Carlos is mistaken. Because Paul's float is rigid, the gas inside it has no "awareness" of outside pressures. It remains at 1 atmosphere. In the case of your BC, the air bladder is not rigid, but changes size as pressures change.
Carlos D
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Joined: Nov 13th, 2010, 12:21 pm
Location: Palmetto, Florida

Re: Tether buoyancy idea.

Post by Carlos D »

Pilikia, I stand corrected, a 1 atm sub, will be at 1 atm
despite external pressure, so if Paul's capsules are
absolutely air tight the darn thing might work!
Paul, I have already self administered 12 lashes, it was so
painfull that I had to chase it with a couple of Mojitos
(with extra rum) :-} Let me know how your tether
buoyancy solution works!
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PaulC
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Re: Tether buoyancy idea.

Post by PaulC »

Pilikia again thanks for the correction. I have yet to implement the idea but since I am on vacation this week and have some let over parts lying around maybe I will do a small scale test, but other than that I don't know how I will test it until the new rov is done this spring. I can wish it were done now, but that would be rushing something that shouldn't be rushed. I know from experience.
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sthone
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Re: Tether buoyancy idea.

Post by sthone »

I think PCV floats would work fine, (I've thought about this myself) except for that fact that they might be a little bulky, heavier than foam, and cause a little more drag but I doubt you would have to worry about losing buoyancy with them. If I remember correctly someone had a chart that said a 1/2" piece of PVC could withstand about 2000 psi, I think that's a little more than the deeps we can reach :)

-Steve
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PaulC
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Re: Tether buoyancy idea.

Post by PaulC »

I too thought about the drag, but I think that not having to replace the foam floats every so often because they have been either waterlogged or crushed outweighs the drag, but really how much do I have to worry about drag. But maybe I am just a sinking ROV.
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Pilikia
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Re: Tether buoyancy idea.

Post by Pilikia »

Watching videos of ROVs turning and twisting around, I've noticed it is common for the tether to loop around on itself. When this happens, the attached floats tend to hang-up on each other. Making a design that allows them to slip by each other easily should be a high priority, it seems to me.
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PaulC
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Re: Tether buoyancy idea.

Post by PaulC »

But in defense of my idea Pilikia it also must be noted that you will have the same problem with foam floats getting caught up on each other. So in that regard I believe that it becomes a mute point, but at the same time I agree with you the thought had crossed my mind. Since we are just "Hobbyist's," and this hobby is all about innovation then I think that I will give it a go. The worst thing that could happen is that I do get caught up with my own tether. More importantly for me is trying to achieve a state of neutral buoyancy with the tether, and not have the floats get crushed at depth; since the floats are rigid (and have mass) and have a precise volume in them it is going to get interesting. I just don't know how many of the floats to make to get the tether to a state of neutral buoyancy. These things are what make this hobby and science fun as well as a learning experience. : :D
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