I've been working on this for the last two years as time has permitted. Pain in the ass to build, but would not be hard to duplicate now that I figured it all out. It has Left, Right, Up, Down, Forward, Reverse controls. Powered by 8 sealed lead acid batteries configured for 24V - 12AH. I lucked out on eBay and got ahold of some Comair 6" DC fans. They draw 3A each underwater and work fairly efficiently. This moves at about 3 feet per second. So far I only use it in fresh water since too much aluminum is exposed. Salt water would wreck this in a day. I only go down about 50' with it, but I think everything is designed to go down up to 500' without leaking.

Waterproofing the fans? First steap is remove the bulky circuit board - you don't need it or any of it's worthless features since I'm not trying to cool anything.

Hall-effect sensors 101. The SS42R has two 5V outputs - great for driving power mosfets. I have one NFET on each coil with a 10k resistor and 20V schottky diode to ground for gate protection. I soldered this on a little protoboard, smothered it with epoxy and there you go - waterproor to any depth the PVC battery tubes can handle. The coils are now liquid-cooled, so I can bump them to 48 volts if I want to double my power.

One has to assume that any lakeside highways where telephone lines were strung have to have some insulators out there somewhere. Not to mention rivers... I guess you could also scope downed poles along RR r-o-w's that go through swamps or run along lakes/rivers. I figure I'll also see bottles out there too.

It's going on its maiden voyage in early July. I'll post pictures.