I recall you said your box leaked when held under water for a long time. Did you make any improvement to your battery case that helps. I have made some progress with adding O-ring grease to the seal of my leaky box. But I am not satisfied its good enough.
I had an interesting conversation with a friend who has done a lot of work for the navy. He said put about 10 lbs positive pressure in the box and that will keep the water out. I got a small air pump that puts out probably around 8 lbs and am going to pressurize both the battery box and the driver box.
The problem is where to get dry air 
I’m still noodling on that, but I think since the pump will be turning on only occasionally (with an anti-backflow valve and assuming no giant leaks) I can just have a small snorkel sticking up and be ok.
Right now this is how I’m hoping to lay out the thing.
It’s much tighter than I had hoped, but I only have 3 components, the air pump, the hard cutoff solenoid and the control board, so I think I can fit them all.
I also found, on closer inspection, that the pressure equalizer valve was very loose in the case. Now I know where the air input line is going to go through.
Ok, well, here is the sum total progress made on the Battery Spot Welder:
Yes, I got a battery.
It is I think 350CCA and wasn’t that expensive. For now I’m just going to monkey around with using the starter solenoid for proof of concept. Primarily I wanted to settle on a battery right away so I could size the box that the whole contraption is going to live in.
The immediate problem to solve is designing and building the welding arms. I have a couple of ideas that I’m going to model tonight.
The great news is I have a friend flying out to Germany early next week and she has agreed to let me order the Malectrics kit and have it shipped to her house there. Then she’ll bring it back for me. Of course this assumes that it comes back into stock in time.
Just for the record I did get the Tilt-pitch-roll sensor working (it was working, just not reporting correctly), made some updates to the display panel code (bug fixes and all the datapoints for datalogging, but no actual uSD logging code yet) and got all the battery cages machined, so all in all a good day.
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Related to the positive pressure thing. I have had success doing the following. On my first build I had a small leak, it did not give me a problem until one day I turned the board upside down to clean weeds off the prop while I was in the water. The water that was sitting in the bottom of the battery box found its way into the ESC, and my battery monitors. Things went erratic. Fortunately when it dried out things were all good.
So I added a short length of that blue silicon tubing that passed from the outside to the inside of my enclosure. Just before I was ready to go in the water I would blow into the hose using my mouth. At probably about 2 psi you will hear the air start to leak out. That’s a couple hundred pounds trying to push that door open. Just fold the hose over and clamp it shut. The trapped air will leak out very slowly. It will probably still be leaking out when your done. Everything will stay dry until the air stops leaking out.
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Kill 2 birds with one stone. I used a tire valve stem. I used a step drill to open up the equalizer hole as needed.
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It’s slowly becoming a thing
I am going to have to cut the tube considerably shorter, otherwise the prop will run into the vertical stabilizer.
So, instead of doing hard things like epoxying the motor and cutting up the board, I designed my spot welder arm.
Also, after reading through Ben Gold’s build I went and looked at boat hatches - I never realized they were so cheap! This may change my plans. Not sure yet.
speaking of battery spot welders I found out an interesting tidbit. I always thought starter solenoids were just a coil, a ram and some contacts. But apparently there’s more to it than that. I attached the metal plate of the spot welder to negative on the battery, and touched the coil terminal with Positive and it clicked just like it should. But if I’m going to use an N-channel FET to drive the circuit I need to pull low. So I attached the metal plate to positive (thinking it’s just a coil) and touched the coil terminal to negative. and got a really big spark.
Then I switched it back to negative on the plate, tried it again and . . . got a really big spark.
So some sort of protection circuit inside the solenoid is missing its magic smoke and has failed short.
Fortunately the solenoid is riveted shut, so I can drill out the rivets and take it apart.
I have the same foil. I just cut the vertical fin off. You dont need it.
Well, this is basically how it’s going to go together. On final fit I found a couple of things I need to fix, so it won’t be attached until next weekend (this weekend I’m going to try to have a life).
In hindsight I’m kind of glad I broke the nosecone up into 4 pieces, I only have to re-print 3 of them.
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Maybe there “was” is a diode inside the solenoid to suppress the inductive kick of the coil.
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After installing the heat press inserts and trimming the unused tabs I think I’m going to have just enough space to fit all the other bits in.
I also picked up a SUP Leash which should work perfectly for my deadman circuit.
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Beautiful 
They say the Devil is in the details, and I must admit there’s a devil-ishly lot of detail work to be done.
My battery box setup needs some re-thinking because I can’t make enough space near a wall of the box to put in all the connectors.
I broke a tap in the copper pieces that I was going to use for the battery spot welder arms and nothing - Nothing - sucks the fun out of a project like tap bits in the work. Shy of EDM you can’t get them out and have to start all over. I did get the Malectric’s kit ordered. I couldn’t get it shipped to my friend’s house in Germany because then I’d have to pay taxes - so I had to get it shipped here. Who knows how long that’s going to take.
My driver box is all but complete except I got the wrong size gland fittings and my new ones were supposed to come in today but because of the snow nothing is moving.
I need to order a selection of adhesive shrink tube.
Before completing the drive unit I needed to take apart the motor and epoxy it, but I had a devil of a time getting the screws out until I finally just broke down and attacked the thing with my MAP gas torch. Then I couldn’t get the driveshaft out shy of banging on it with a big hammer, so whether the bearings survived is to be seen.
I gooped the heck out of these things with epoxy - I still need to address the rotor leads, but the rest is a big mess that won’t cure because the shop is too cold.
My new mast came in, though. It is indeed longer than the old mast.
The box for the display came in, so I am going to spend the rest of the day today wrapping that up. One thing I didn’t realize about fishing tackle boxes is they are hinged and open on both sides, with a plastic plate in the middle. I’ll need to remove parts of that plate to install all the bits. And that definitely doubles the possibility of leakage.
Lastly my leash came in - it’s really nice.
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You sound like you have your hands full! Hang in there! I’m about to get some work done on my project and I know it will be tedious too haha!!
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I hear your getting dumped on with snow right now. Winter storm. So lock yourself in the garage and play.
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That’s exactly what I’ve been doing - hunkered down in the shop. Haven’t had any actual human contact for like 4 days now…
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@michion Are you sure the vertical fin isn’t needed? I have just sketched my build in ptc creo, and i have to put propulsion unit above the fin…
Mine is working well without it. Of all the foils I own, this was the only one with a vertical fin. I would rather have the motor pod further down.
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Well, the battery spot welder was a much bigger distraction than I had hoped (though deep down I knew this would be the case). First, I’ve never worked with big blocks of copper before, and I quickly found out that it doesn’t take much for a block of copper to best a drill bit and it really doesn’t take much for it to best a tap.
However, after much frustration and a lot of bad words I finally got the arms put together.
The Malectrics kit arrived shortly thereafter and I spent this morning (when I wasn’t re-making my battery cages for the FOURTH TIME!) putting it together.
However, near as I can tell there is a big bug in the firmware in the kit. It has an auto mode, which I guess is designed for you to drop a battery in and it’ll automatically fire after some number of seconds. However, I was still trying to figure it out and was down there aligning the nickle strip when the thing fired on me, threw a bunch of sparks and scared the crap out of me.
There is, so far as I can tell, no way to turn Auto off. So I’m either going to go hack the source myself or I’ve sent Mr. Malectric an email and maybe he’ll be kind enough to add a Manual mode to the thing so that it only fires when you push the foot switch (IE, the way it’s supposed to work)
Also, the battery I got, which is a lead acid motorcycle battery with 350CCA, seems to have a serious voltage drop (like it drops down to 4 volts according to the Malectrics readout). So I guess I’ll be adding those cheap knockoff supercaps anyway.
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that is wierd, i can set mine in manual, i only use the foot switch, auto mode is faster for building but it fires as soon as there is conctact … too scared to try it …