Needing to bounce some DIY DPV ideas off some DIYers...

[Tao of the Dive]

So I started at the typical place of taking a trolling motor, put it in a housing, add a battery, figure out a way to seal it up keep it from collapsing and viola. Well as I've researched, each compartment of the idea has evolved. I'm still on the drawing board, and I do not like to waste time on ideas that do not work, so I tend to take an idea and reach for an ultimate conclusion. Anyhow, This is where I'm at;

Body: I've sourced PVC pipe in diameters of 10" and 12" with matching flat end-caps. This is not my favorite choice, but when you read later, you will see that it makes for a somewhat decent choice. Product Listing PVC-Caps-Flat

Power: I'm waffling on sealed batteries of course, mostly of the gel variety. Lead acid seemed to drop voltage too much. Sizes vary from lawnmower sized combinations to a set of Optima batteries. I recently found out that optima batteries can tolerate 150 foot depths, and all you have to do is waterproof their terminals. So this was good, will explain in next section.

Pressure protection: Okay, here is where i went off script from most DPV build threads I've read. I knew that waterproofing/pressure proofing was going to be difficult. I've since developed several options to test. Mineral oil. I saw where some PC builders had taken to building computers, and dropping them in mineral oil for cooling and esthetics. The mineral oil was electrically inert, so the energy didn't cross circuits and short. This gave me the idea to fill both the engine compartment and battery compartment with mineral oil to defeat the pressure and leaks, since it wouldn't be compressible then. Also, mineral oil is lighter than water, so it might help in reducing the amount of negative buoyancy. The downside to using this, would be that in order to take the unit apart for battery change outs or motor change outs, I'd have to have a cradle in a tub in order to catch the oil, and it would be messy as hell. Cleanup in order to re-solder wires would be a massive headache. Potting: I realized that I could pot the circuits, battery, even motor if I had to, in epoxy. But most marine epoxy's were somewhat weakened by sunlight. Some epoxy's were weakened by water. Then one night at bowling league, I realized that bowling ball epoxy was very stable. And slightly buoyant. So I sourced Easy-Strike. Roll with the best. . Due to potting of the batteries, I'd have to verify all my connections were solid, worked, then pot the battery in epoxy. The idea is, pot it in a round shape so it will easily slide into the chassis, and the wires would route out of the potting material via a marine grade connector, allowing me to connect a harness to charge the battery inside the chassis, even while it is potted. This would also prevent any shifting of the batteries. Wet: With the optima batteries being tolerant of 150 foot depths, and me not having a need to go below that, I figured okay, just pot the top of the battery where the connectors are after I make my primary connections, then let the battery rest in the water. Drill some holes along the top and bottom of the chassis like a submarines vents to allow trapped water or air to vacate the chassis. Motor, speed controller, connections would all be potted in a similar fashion. In fact all voids in the unit could be potted, eliminating any air which would allow for implosion.

Motor: And then I heard about brush-less motors. I'm still researching these, but it is my understanding that these motors can run in salt or fresh water and suffer no damage. Granted it lessens the lifespan, but at 100 a pop for a motor versus 500 for a used Mako engine, I'd say that's easier to stomach. They are capable of high torque, high speed, are far more efficient and are all the way around great motors. HobbyKing R/C Hobby Store : Turnigy 80-100-B 130Kv Brushless Outrunner (eq: 70-55) . Since rimdrive and hubless motors are still in their infancy, I need a motor which will drive the prop strongly. So I can either pot this motor or run it wet. Versatility is a beautiful thing.

So, do any of you DIY guys see any faults in my thinking or ideas that I do not or cannot see? Any ideas which might expound on what i put forth?

[fjpatrum]

My only real thought about all the potting and filling voids with mineral oil would be surface weight and overall cost. I don't know enough about DPVs to know whether your other ideas are reasonable or not...

[WhiteLightning]

I don't have any advice to give, but I am interested in your progress as you move along with this project! Please do keep us updated!

[Tao of the Dive]

Good news, I was able to source a prop finally that was not a trolling motor prop. Trolling motors always struck me as slow, flimsy, fragile, and not purpose suited. This prop...changes that. six bladed, scimitar design similar to the shaping of a nuclear subs props. It's a prop for a boat thruster. This could be the one I've been looking for. Even at slow speeds, this thing could move enough water to move a DPV and three people at a pretty good clip. http://www.jamestowndistributors.com...11673&type=pla

I'm still trying to gather estimates on the Turnigy motor hooked up to two deep cycle optima batteries to get an idea on run times though. I am wondering if I should try gearing this motor down and if so, how.

[350xfire]

This sounds like one of those projects that looks good on paper and once you get through flooding the thing about 3 times and spending as much as you would have on a new one, you might get it right... might! lol!
Good luck with it. Sounds cool though.

[Tao of the Dive]

If I go wet with it, wont be much to flood...lol

[350xfire]

Indeed!

[gsk3]

Um someone's mentioned surface weight but what about submerged buoyancy. This thing's going to be massively negative, as anyone who's flooded a scooter can attest. Unless I'm misunderstanding your plans....

[Tao of the Dive]

Um someone's mentioned surface weight but what about submerged buoyancy. This thing's going to be massively negative, as anyone who's flooded a scooter can attest. Unless I'm misunderstanding your plans....

Actually, if I use the mineral oil, since it is oil, it will be almost positively buoyant. However I'm not leaning in that direction. I'm looking to have it as a wet unit...meaning essential items will be potted in bowling ball epoxy. If i went in this direction, i was going to mold an air bladder into the top running the length of the DPV, and if it was too positive i was going to trim it out with small amounts of lead or zinc.

A recent test of some bowling balls showed that most were positively buoyant. But since i wont have to worry about protecting items from moisture or pressure, i can make the device shorter and smaller. And even if its too heavy in the water, I can still add an air bladder to trim it out. From what i can tell, most upper end commercial units are in the 60-85 pound range. So far, my math is pointing at about 75 if i go wet with the design.