Attached is a document written by a colleague of mine on the use of hot glue to seal solder joints. I have tried it and found that it works quite well.1487-SessionIV_Rowe_HOTGLUE.pdf (4.15 MB)
A very interesting talk- thanks for sharing this with us. The material is quite timely for those kit recipients who will be making up their thrusters shortly.
I put together thrusters for 2 ROVs last week, and have been grappling with ways to do it better in terms of preventing ingress of salt water to the joint. I did make a couple of modifications on the fly, which seemed to help things. First of all, I left off the outer 1/4" heatshrink for now, since it seems like this is just needed for neatness and cable routing purposes, and will serve as a large trap for saltwater. Once I see how the thrusters are going to mount, I'm going to try to use a small cable tie or two in place of the outer heatshrink. The second thing I did was use 3/32" heatshrink on the individual wires, rather than the called out 1/8". The 3/32 fits OK if you keep your splices nice and tight, and seems to do a better job of sealing onto the wire with the tacky liquid tape on it.
After all that, I started thinking about some other type of packing material for inside the heatshrink, to replace the last layer of liquid tape. If I were to do it again I was going to try glopping some silicone grease inside the heatshrink, and then shrinking the tubing in a linear fashion to squeegee out all the excess, much the same as is shown on page 14 of the paper. The idea of using hot glue never occurred to me.
I did have a question about the paper, if you don't mind asking your colleague the next time you see him. Is there a preferred technique for melting out the hot glue if you're going to re-do the splice?
Thanks again for the post.
Thanks for posting this Chris! We'll try this technique on the next build. I second Walt's question about preferred method for melting and re-soldering.
I’m glad to be a part of this community, and I’m happy to pass along tips like the one I posted. Thanks for sharing the details of your most recent build process. Good stuf to know!
To remove the hot glue from a joint, I use a heat gun to soften it, and while the glue is soft, I use a wood toothpick or the wood handle of a cotton swab to pick the glue from the joint. What little bit that remains burns off when the joint is heated with a soldering iron. You can also soften the glue with isopropyl alcohol as shown in this video - www.youtube.com/watch?v=dNNqSXgj6DE I only use that method when I’m sure that it won’t damage the insulation.
I’m glad to have helped out. The real credit goes to the guys who came up with the idea. Please check out my reply to Walt, regarding how to remove hot glue.
Allow me to put my input in on this:
The technique is spot on with the techniques used on competition level underwater robotics. However, hot glue is really not the best sealant(IMO), especially with wires that either flex a lot or are going to deeper depths.
If you follow these directions, but instead use a two-part epoxy or a proper underwater sealant instead, it tends to work much better in my experience.
One of the better methods is with scotchcast, and explained on tech report page 6 here: http://www.mpcfaculty.net/jill_zande/Carl%20Hayden%20ROV%20Tech%20R...
this was the method that was being discussed in the original power point, but when you have the time and ability to produce connections this way, they tend to work out the best.