Go easy as I’m a newbie in the underwater robotics world.
Looking at getting some advice with regards to the blue robotics subsea cable (PUR Subsea Cable).
I will be connecting this to my own motor therefore will have to solder the wires. I am worried about pressure pushing in between the cable and the copper and that it would travel all the way through the penetrator, therefore leaking into the enclosure. What is the most common method that you are using to join these together at the start of the subsea cable?
If I have this setup. eg. My motor → 3 wires → Solder to 3 wires of subsea cable → cable through penetrator.
How do you suggest I solder the wires? I am looking to build 3D printed enclosure filled with epoxy ensuring they don’t short? Wondering what is the best and cheapest (but reliable) method as I have 10 penetrators so whatever the cost of doing one is 10x per each vehicle.
You definitely need to pot cables where the end is exposed to the water. Rest assure that the water will travel internally in the cable otherwise. Do not use hard epoxy for potting as this has a great risk of leaking. Use potting that are made for the purpose, like the 3M Scotchcast 2131-B
They are not very cheap but a lot less expensive than doing it all over again with new equipment because the first attempt failed and drowned. Please don’t get me wrong here, but if you try to go for cheap solutions when mixing electronics and seawater, you will learn the hard way as so many others.
I would also recommend (as a minimum) a connector for the tether
To avoid water entering the end of a cable, it needs to either be sealed or enclosed.
In our thrusters and motors we currently use a flexible marine epoxy, which is visible in our M200 usage guide. Note the strain relief used on the cable to avoid excessive bending at the epoxy joint, which could cause it to peel off the cable jacket if it is stretched too far on a bond with poor adhesion.
If the cable connection area can be fully isolated from the moving components then it could also be possible to turn it into an enclosure, using a penetrator for the seal (or something similar) instead of sealing the wires themselves, although it’s worth noting that for operating at depth an air pocket can be an implosion failure point.
People sometimes also use oil-filled enclosures to provide a water-free and pressure-resistant volume, which is another possible option, with the benefit of being more maintainable than epoxy, but quite messy, and still potentially challenging to seal well enough that the oil stays in and the water stays out.
