Pressure problems and water infiltration


#1

Hello everyone, Lou here. :-)

Thanks for accepting me into the group. I was watching the video that showed the ROV leaking at depth.

Have you considered using mineral oil inside the clear shell? Being in the computer business, I have seen working pc's being cooled by circulating mineral of which the electrical parts were submerged causing no harm to the parts.

example: http://www.engadget.com/2007/05/12/puget-custom-computers-mineral-oil-cooled-pc/

that being said, if the clear shell were filled with mineral oil, it seems reasonable to believe that there would be an equalization of pressure. no more bursting at deep dives. The ballast will have to be reconsidered.


Manufacturing a shell for deep dives at 1000m+
#2

Hey Lou,

Filling our electronics chamber with mineral oil (or some other non-conductive fluid-- liquid compensation) has certainly been considered. The issue with doing that with this specific design is that it is built to be neutrally buoyant(ish) with the chamber filled with air. If we filled the Electronics Tube with mineral oil, it would be considerably heavier and a lot of additional flotation would be needed to keep the ROV from sinking. Additionally, we'd have to figure out a way to focus the camera (since it would not have an air-glass index of refraction difference any longer and the air gap in the lens system it comes with probably wouldn't handle much pressure). We would also likely encounter issues with the brushed DC motor in the tilt servo. Finally, filling the Electronics Tube with mineral oil would make everything a lot more messy to tinker with, which at this phase we do a lot.

That being said, liquid compensation would certainly improve the depth capability of the tube as well help with heating issues. If you (or anyone else) wants to experiment with it, it would be really awesome to see what comes of it!

Right now, I'm working on a modified endcap design that would incorporate a thicker o-ring that may hold a better seal even with the wide tolerance bands of the tubes (which ultimately is why we have trouble sealing a lot of the time). I'll be sure to post how that endeavor works out, and please keep us posted on any other thoughts you have for leak prevention as well.

Thanks for the idea!

Eric


#3

Lou,

can you point me to the video showing the leaking you were talking about?

Thanks,

-Stefan


#4

A spot for all who work on oil fillings

Environmental protection in the event of a malfunction

Sorry if I sound like a teacher, but I think we all want to explore the seas and lakes and not kill


#5

Actually, you would use a marine-safe hydraulic fluid, HO-32 or similar. The deepest diving ROVs in the world use hydraulic thrusters and oil filled enclosures; using these types of fluids. They are selected for the high biodegradability and non-toxicity on marine life.


#6

@Eric Stackpole,

Have you considered quad seal O rings ?


#7

You know, Evilmacaw, that’s not a bad idea. I had experimented with quad seal o-rings early on, but haven’t really tried them out in the context of the new endcap design. It seems plausible that the difference in how quad o-rings engage with the surfaces they’re against, that leaking would be less likely and larger tolerance bands may be acceptable. I’ll order some from McMaster-Carr now. Thank’s for the tip!

E


#8

Eric Stackpole,

Along with quad seals you might want to look into stack seals an O ring under a teflon square seal ring commonly used as the piston seal in Hyd . cylinders or adding a side shim ring with the O ring or Quad seal causing the sealing surface to stand more "proud " by limiting seal squash .


#9

Eric did you ever follows up on using x-rings? I’m curious how they might perform.


#10

About the time of the previous posts (Nov 2013), we ended up switching to a larger-diameter single O-ring, which was then introduced on the 2.6 model. The larger diameter of the O-ring was better able to handle the unit-to-unit variations in the size of the acrylic main tube, and the incidence rate of flooding dropped greatly.

At this point, if your O-rings fit properly during initial checking, and you keep them properly lint-free and greased, then there shouldn’t ever be a problem with water leaking past the O-rings. Also note that (on 2.7 and 2.8 units), the strap that holds the main tube onto the chassis needs to be kept really tight- if not, then heating of the internal air by the electronics can cause the tube endcaps to pop off when you surface after a long dive. This effect can also be minimized by leaving a partial vacuum in the tube when doing your leak check- after you pull a vacuum on the main tube, replace the syringe plunger before the air pressure has totally equalized, leaving a partial vacuum in the tube.

-W