Homebuilt ROVs Forum

Hi everyone,

I have been working on an underwater connection system for my sensor project, and thought it might be relevant to folks here:

http://edwardmallon.wordpress.com/2015/ ... or-system/

So far these things have not been any farther than the laundry tub, but I though I would post here it to see if someone with more experience could give me some feedback on the idea. Has anyone tried a multi-section tether before? Changing the length of the connector pipes is easy, and lets you vary the buoyancy of the cable (provided your wires are long enough), so might be a good way to make the whole thing neutral.

cheers.

Hello Edward. Thanks for link to blog - interesting reading and some very familiar challenges. I've used very similar barbed couplings, but with a flat washer instead of the swivel thing. The swivel seal looks like it would hold up better to external pressure. I have not seen them while lurking in the plumbing isles at the local hardware though.
Instead of the threaded tubes (used those in other projects) I used 2 back-to-back PVC adapters. Not for buoyancy, which is a novel idea, but just as somewhere to fold the wires up in. Yes, the wet sanding too
Scratching or machining in radial grooves I also did for fear of the plastic being too slippery for a decent epoxy bond. PVC would be better, but couplings of this size and type not readily available.
While often compact enough for a single connection, I dropped the hose barb coupling approach for thruster and other connections in the ROV where one would need many. Just too bulky for me. Have yet to come up with a more compact solution for my Sonar connector. This has modified DB9 connectors inside.
Problem with any housing cavities at surface pressure is that you always take a gamble with leaks. For something that has an investment of months this is a worry. Larger housings that can be monitored from outside can have leak detectors fitted. Guess you could do the same with the tether junctions. Oil at ambient pressure needs care to be taken to make it work, but it is in my opinion the most reliable.
Very interesting environment you are working in. Currently I'm involved in a non-ROV self-funded fish research project. All ROV technology however. Possibly this will lead to something more in the future.

Cheers,

Ross

The thing I like about the swivel mechanism is that it applies pressure to a hard plastic lip on the other side of the cone washer, so as you tighten the nut there is no rotational force being applied to the parts forming the water tight seal. These fittings are also available in brass for the same price, and the o-ring seats are MUCH cleaner on those than the polymer adapters, because there are casting seams on the plastic adapters which have me a bit concerned. But I don't know how well the brass will fare in marine environments.

Thanks for the leak detector idea... the sensors I am working with only need 3 wires but my multi conductor cable has 4. which means that potentially I could use that extra wire in some kind of leak detection capacity...I must think some more on this.

I could also use some advice on multi conductor cables. I have been re-purposing the MC-12 series extension cables from Omega: http://www.omega.com/pptst/M12C.html
because I need the soft silicone jacket&insulation to position my sensors. PVC jacket stuff is too stiff for this, and just doesn't "hang right" under water. I was wondering if someone on the forum here could suggest a supplier for 24awg four conductor, silicone jacket&insulation cable. The Omni cables cost about $2.00 / m if you buy their longest 15m lengths.

I am happy to report that the first underwater trials of the diy underwater connectors have been a success:

http://edwardmallon.wordpress.com/2015/ ... e-strings/

They survived more than 4 months at 10m depth, though I admit they were not subjected to the kind of knocking about that a typical ROV tether would see.

Impressive reliability and low power consumption via innovation and cheap materials

I finally completed the set of logger build tutorials on Youtube, to go with the screw terminal logger posted in 2017. Includes more detail on how I make those underwater connectors:

Epoxy the sensors & build waterproof connectors
https://youtu.be/EKNNDPGr1Aw

The latest update to our underwater housings made from PVC. Fewer parts & much easier to assemble.

https://thecavepearlproject.org/2020/04 ... 20-update/

The basic idea would be easy to reproduce with flange ring if you don't have access to the formufit parts, though I admit flow/streamlining was not a huge priority in our application. Could be reproduced at many different scales, perhaps as an oil-filled motor housing?