Hi Guys
Just recieved my thrusters today, they look great! Thanks for all the hard work!
Just wondering what the potting material is? Can you please tell me the supplier and part number? How did you select this specific material?
Thanks a lot
Ben
Hi Ben,
Glad you like the thrusters! The potting compound used for the cable on the T100 Thruster is Loctite Marine Epoxy. You should be able to find it at most hardware stores or online. We used this compound because of its excellent performance underwater and high viscosity, which allows it to be used on connections without flowing everywhere. We use a syringe to apply it but you can also use a toothpick or similar.
You’ll hear more about it in a blog post in a few days, but we’ve tested the potted connection to a depth of 3000m successfully.
Here’s a link to the product on Amazon: http://www.amazon.com/Loctite-1405604-0-85-Ounce-Plastic-Syringe/dp/B000H6A3D6
I hope that helps.
Best,
Rusty
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What is the jacket type on your raw cable? Is it PVC, PTFE or what? From the look of it, it is some type of thermoplastic material … just don’t know which one.
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Harold,
The outer jacket is urethane - it’s super tough but a little hard to get potting compounds to stick to sometimes. The conductors inside have Teflon (FEP) insulation that has been chemically etched to improve adhesion to potting compounds.
-Rusty
Cool … TPU … actually urethanes are pretty stinking good for the jacket. The problem with potting compounds is the type of compound. Get away from an epoxy based material and go with a urethane for the potting of your connections. Urethanes LOVE to chemical bond with other urethanes and depending on how you treat your pass through area it will bond well to a lot of other materials.
One of the problems with the epoxy is the Thermal Coeff. of Expansion … that and “bond” sites. If you are going to use epoxy, check with the OEM on your cable and see what type of urethane it is that they are using and get some recommendations from them. What is the material of the rest of the area that the cable is going through?
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Harold,
We’ve tried a few urethane potting compounds but haven’t found a great option yet. They seem to be very sensitive to exact proportions when mixing.
On the thruster, the cable is soldered to pads on a PCB and then the whole area is potted with epoxy. It works pretty well and withstood the 4500 psi testing without issues. On the BlueROV, the pass-through is anodized aluminum and should adhere well to most things.
-Rusty
On your pass through for the BlueRov … have you considered using a stuffing tube design? No potting required and they work really well.
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Yeah. We’ve been looking at these from SealCon recently. They are only capable down to 300 ft but I believe there are versions available for great depths.
-Rusty
Hey Rusty and Team!
I have just started playing with potting and epoxy and I am very curious… how do you actually get the mixed epoxy INTO the syringe before dispensing? I know… I know… sounds like a silly questions…
Last night I was never able to get more than a few drops of epoxy into the Syringe. When I did, it seemed that I introduced air bubbles into the mix, and it took a while once dispensed, to work all the bubbles out.
In your videos, it appears you have half the syringe full! Am I missing something? Do you suck it up through the needle, or feed it in from the top with the plunger removed? Any tips?
Ryan,
Good question! We just prop the syringe up (sometimes in a vise) and pour/scrape the epoxy from the mixing cup into the syringe (with plunger removed). Once you replace the plunger you have to flip it over and let the bubbles rise. Using this method is pretty quick to fill to 75% full.
We use these syringes, needles, cups, and mixing sticks: https://www.bluerobotics.com/store/tools/tool-potting-kit-r1/
Hope that helps!
-Rusty
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Looking at the BlueESC’s in the T200 thrusters, the potting compound around it is translucent. Is marine epoxy still being used to waterproof the BlueESC’s? My experience with Loctite 2-h set marine epoxy is that it cures into more of a white color.
Hi Michael,
The BlueESCs are potted with a combination of MG Chemicals 832TC (thermally conductive) and MG Chemicals 8322 (clear). We use the Loctite epoxy to seal some sections before potting the rest.
-Rusty
Hi, after reading a lot about potting and epoxy I have one question, will it be possible to use silicone instead of epoxy?
Regards
Erik (Norway)
Erik,
Silicone is great as a void filler and that is about it. It is not a material that has a lot of adhesive properties when you are trying to seal.
If you can get a hold of polyurethane casting material that would would pretty well because the jacket of the cable is a thermoplastic that should be friendly to urethanes. The only issue with life is the interior of the penetrator shells. The anodize coating is not a good layer to bond to and you would have to locally abraid it and use primers.
That is why in the thread I mentioned using stuffing tubes vice a potted design. Less pain in the rear and they can handle a lot of pressure. I have multiple cable systems that I deal with at work that handle up to 1000 psi using a rubber packing etc.
Hi
That little tip for filling the syringe could be in your assembly guides. It would have saved some time and some hairs on my head.