Non conductive liquid


#1

My 2 cents worth

Is to use a non conductive liquid that will help stop crushing, see link below

http://solutions.3m.com/wps/portal/3M/en_US/Electronics_NA/Electronics/Products/Product_Catalog/~/3M-Fluorinert-Electronic-Liquid-FC-3284?N=4294412714+5153906&Nr=AND(hrcy_id%3AZ3RW6H606Tgs_2ND8BCWDVL_N2RL3FHWVK_GPD0K8BC31gv)&rt=d

Craig


#2

Hey Craig,

Thanks for the link. Florinert would be pretty fun to play with, but it's pretty expensive and still creates some of the same problems as other more regularly available non conductive liquids we've looked at like mineral oil. Namely, the added mass of the liquid would cause the ROV to no longer be inherently close to neutrally buoyant, and the camera would not necessarily focus the same way.

That being said, I think there is a lot of potential in pressure compensation, and we've been looking into options that might be useful in future designs.

E


#3

No prob, just a thought.

I wonder what helium would if it was added to the liquid?

Good luck
Craig


#4

Helium is an inert gas, so it won't bond with any other elements, and it will remain in the gas phase unless it is in some pretty extreme conditions. If your thought was that helium is very "light" so that adding it to something would make that thing lighter, there are a few things I should point out that you should make sure you're considering...

The first point is that although we think of helium as something that reduces the weight of things it's attached to (like a helium balloon lifting a paper clip), it actually has a weight of its own that gravity pulls downward. The only reason it rises upward is because it's less dense then air at atmospheric pressure. Think of it kind of like a piece of wood in water. The wood obviously has an appreciable mass, but its density is less then water so it floats. In the same way, a helium balloon is trying to float up to the surface of the atmosphere where the density of air is equal or less then the density of the balloon. If you could have a container the same size and weight of a balloon, but instead of filling it with helium, you filled it with nothing- that is, a complete vacuum- it would actually weigh less then if the balloon was filled with helium! You may already understand all of this, but it's an important thing to point out for anyone else reading this who may be trying to follow the concept.

The second point (which is really just an extension of the first point) has to do with the concept of displacement. Things are made to float by how much mass they're moving out of the way. If a cylinder were filled with a certain quantity of one material (like florinert) and you added another material (like helium) without changing the volume, you'd actually add mass to the tube, and it would be less buoyant then before!

I suppose our goal should be to come up with the least dense, least messy, least cost, non-compressible, non-conductive material possible to fill our tubes with. We've been working on some crazy ideas here at OpenROV for that (which I hope to make a big post about soon), but in the mean time, please keep the ideas coming!

Thanks again for helping with the brain storming,

Eric


#5

Thanks Eric very interesting.


#6

Maybe I'm naive here, But couldnt you in theory increase the air pressure inside of the tube before it goes down to try and "pre-equalize" the tube. Obviously this isn't going to be an amazing solution, but maybe you could squeeze a little more depth out of it. This concept worked for me when I was using some pretty ghetto seals a month or two ago. I was trying to get a little more depth out of a waterproof aluminum box POC I was working on (note, we are talking about only like 50-60'). I just snagged a bike pump valve with a sealing cap I had laying around and put it on the box. I sealed it on the inside with a pressure washer I also had. Like I said, the seals were not very good so the air slowly leaked out, but I got to where I needed to be.

Once again, just throwing out ideas.

Cannon


#7

Hi Cannon:

Your idea is sound, but unfortunately it won't work with the current OpenROV design, since there is nothing mechanically keeping the endcaps from popping off. If you redesigned the endcaps, maybe added some flanges that you could use to tie the endcaps together with some threaded rods, then yes, one could do just what you propose.

As to the endcaps popping off, we have actually seen this happen before on a couple of dives. If you get a water leak when you're at depth, when you go to surface the ROV, the interior of the tube is now pressurized just a bit since some of the volume of the tube is taken up by water. The tether handler sees the ROV coming to the surface, and then when its only a couple of feet away, there's a huge whoosh of bubbles as one of the endcaps pops off, and the whole tube floods. Pretty exciting stuff.

-W


#8

Whoa - I don't want to imagine the encaps popping off under water. Probaly I'll sercure them with some strap so that they can withstand at least a little surplus pressure from inside on my future dives. Thanks for pointing that out, Walt.

If the encaps were properly secured, we'd seal the syringes and we'd add some air pressure into the tube before a dive - what would happen with the o-rings when they move from the outer rim of their groove to the inner rim when the inside/outside pressure ratio changes at a certain depth? Would they leak?

-Stefan


#9

I think there is some potential here to have some fun making modifications. I already have a couple of ways I think I could make this work pretty simply. (This is the fun part!)

As for the tubes popping off… That happened to me the other day. No fun at all.

-Cannon


#10

I've used Florinert exactly for liquid compensation in the past; it works beautifully and cleans up nicely (it evaporates!) but it is EXTREMELY expensive. We dropped easily $1000+ for Florinert for our vehicle. Also Its really bad for the environment (its pretty much a pure CFC I think)