Looking for a unique DIY project

[fjpatrum]

I liked his idea but I was thinking that it wouldn't be easy to keep water out of the engine.

For the exhaust he could attach something akin to a 2nd stage as well. I think his initial design was too complicated and it won't work. A regulator type exhaust chamber would keep it water free enough, and whatever water does get in would probably turn to steam from the heat.... and he could also vent it straight into the water provided the exhaust valve was mounted deeper than the exhaust outlet from the engine. The problem then becomes thinking in 3 dimensions..... what happens if you go upside down with it?

I don't know how much air it would use but his idea of using a regulator to deliver air on demand certainly wasn't bad and I think it's worth doing some calculations to see if it's feasible.

The big question becomes this: how water tight can the inlet connection be? Because even a small amount of water in the engine will turn it off. This will need to be very robust and I'm not at all convinced that it would work without a lot of modifications. Also lawn mower engines have moving parts that will be in direct contact with the water, which isn't going to make it work better....

What might work better is to make a dry chamber out of a water tight box. The box would house the entire engine so even the moving parts don't contact the water. The box could be kept at ambient pressure with a scuba regulator, which would avoid all of the problems with heat melting the plastic bits and the engine could be supplied with any air it needed by the regulator. Exhaust would still have to go via an intermediate chamber into the water. We once helped a guy design a dry box for a hobby submarine what worked exactly like this, although his sub used an electric motor.

R..

Your last paragraph is exactly what I meant by a "sealed chamber for the engine". I think using a reg for air input is a really good idea, I just think he's going to find he needs a lot more airflow than he expects. Combustion actually takes quite a lot of air. Yes, it can be done, (we've had diesel submarines for what--70 years and steam subs before that) but I don't think you'd get any real gains in efficiency or ease of use/design.

Hence my statement that the NRE (non-recurring engineering for non-engineer types) involved would probably put the effort far too expensive compared to using existing electric motors. It works really good for large scale submersibles, but for small "recreational" single person vehicles, I don't think it would be cost effective.

It would be a very interesting problem, though, and certainly fun to design/build, if that's the impetus for this project.

---------- Post Merged at 03:28 PM ---------- Previous Post was at 03:15 PM ----------

Ok so i found some great 55lbs trolling motors for about $370.

For the hull: Could i build a frame our of wood (maybe with some metal reinforcements) and then just fiberglass over the inside and out. Leaving the wood completely sealed? Could i even use polyurethane foam in some places (curvy bits because its exceptionally sand-able)? Would water have any chance of getting in if i really covered everything? I was thinking that maybe a flooded hull with sealed off electronics might be beneficial. I know it would add alot of mass, but I wouldn't need counterweights, so it wouldn't weigh a ton out of water.

I will see if i can scan some drawings in soon to see what you guys think.

Stitch and glue kayaks are basically a sandwich of 3-6mm plywood between layers of fiberglass (sometimes only the outside is glassed) that are literally "sewn" together at the edges of the wood and then "glued" to fill in the seams. They are very good at keeping water in or out if the builder is good at wetting out the glass and filling the weave properly. You could feasibly build a hull with just this type of build and not need a "frame" per se.

Foam could work for some parts but joining the foam with any non-foam pieces can be a bit of a pain. There are glues that will definitely work, but I wouldn't trust the foam as a structural component. Maybe a nose-cone or use it as bulkheads between chambers but nothing truly structural. It does sand well, though, and would reduce overall weight.

Potting the electronics would definitely be beneficial but makes it impossible to repair anything in the future. I'd make sure you test everything very well before doing that or just forgo it and consider "coating" individual components without potting everything.

As for your trolling motors, while weight may not be an issue in the water, requiring a crane to get the thing from boat to water might be a little too much to ask for in non-scientific environments. There are quite a few motors out there designed as "axle motors" for bike and electric motorcycle wheels that should be significantly lighter that would work well for pushing a screw. I suspect you could get quite a bit of torque from them and get a good in-water speed, with some careful selection of components.

 

[bshey]

by 55 lbs, i meant 55 lbs thrust, the motors weigh significantly less. the batteries though would be decently heavy. In order to try to keep weight down, i thought i would have a flooded hull in order to keep the weight as low as possible out of water. Also i wouldn't need to worry about having a sealed hatch or something. Is this going to be an issue?

 

[fjpatrum]

by 55 lbs, i meant 55 lbs thrust, the motors weigh significantly less. the batteries though would be decently heavy. In order to try to keep weight down, i thought i would have a flooded hull in order to keep the weight as low as possible out of water. Also i wouldn't need to worry about having a sealed hatch or something. Is this going to be an issue?

55 lb thrust makes much more sense.

As for the flooded hull, the biggest issue I see is how to deal with the electrical connections. The electrical connections will need to be sealed well, either through potting, coating, or installation in a sealed dry chamber, but there's no reason you couldn't flood the thing as ballast. It's possible that there might be some "handling" issues if the hull doesn't completely flood and there's room for water to move around during acceleration/deceleration but I don't know why it wouldn't be feasible. That's what submarines do for ballast, right?

I don't know enough about it to say whether or not it would work on a "scooter-esque" size vehicle but it's certainly worth a try. You'll need to decide a neutral buoyancy depth and design the hull to be neutral at that depth, and then determine the best way to do the rest. Obviously you don't want to go rocketing to the surface if somehow the ballast tank doesn't remain flooded. Likewise, you don't want to be dragged to 200 feet if it floods when you're not prepared for it. (Conversely, design the hull how you want and take a few "surfaces and controls" dives with it to determine neutral depth etc.)

There may be a difficulty in how you flood it. IE, having some way to flood it when you want means there is some way for water to enter/exit when you don't want it too as well. Coming up with a bung and gasket or something you could use easily and not worry about losing could be a concern.

 

[DennisS]

An ROV is a good project, you can make the electronics as simple or as complicated as you want

ROVER - Brought to you by the MATE Center

Underwater ROV

Do It YourSelf – ROV project




If you are planning on Aerospace engineering, something like this with a wireless video camera would be a fun project


http://store.diydrones.com/category_s/28.htm

 

[bshey]

i am a pretty skinny person, and get cold on dives regularly. I currently use a 5 ml wetsuit with 3/5 hooded vest underneath. I was thinking that maybe some sort of electronic heating system might be a good lower caliber project, that i may be able to do on the side of another project.

Here is what i was thinking:

A rash guard top and bottom stitched together with flat rubber tubes running over the whole thing. This then get stitched in the inside of a thin shorty wetsuit/skin to hold the tubing in place. The inlet(s) and outlet(s) are then connected to an electric pump and to a heating element, so that the water is heated before each circulation. Its kind of like one of those water circulation cooling suits worn under space suits and by fire fighters, but instead of cooling the water, you heat the water. This unit can be worn under my regular wetsuit (i have plenty of room to fill in the torso area). I could carry the electronics in a pouch type weight belt (i use an integrated weight bc).

Is this a ridiculous idea, or is it feasible?

 

[fjpatrum]

i am a pretty skinny person, and get cold on dives regularly. I currently use a 5 ml wetsuit with 3/5 hooded vest underneath. I was thinking that maybe some sort of electronic heating system might be a good lower caliber project, that i may be able to do on the side of another project.

Here is what i was thinking:

A rash guard top and bottom stitched together with flat rubber tubes running over the whole thing. This then get stitched in the inside of a thin shorty wetsuit/skin to hold the tubing in place. The inlet(s) and outlet(s) are then connected to an electric pump and to a heating element, so that the water is heated before each circulation. Its kind of like one of those water circulation cooling suits worn under space suits and by fire fighters, but instead of cooling the water, you heat the water. This unit can be worn under my regular wetsuit (i have plenty of room to fill in the torso area). I could carry the electronics in a pouch type weight belt (i use an integrated weight bc).

Is this a ridiculous idea, or is it feasible?

There are several manufacturers of electric "warming vests" right now, but I believe they all use straight resistance and batteries to produce the heat.

Other than the pump being annoying and bulky I think your idea has merit. That's how hard hat divers stay warm, after all, on deeper sat dives. They pump hot water into a special layer of their suit, I believe. In that instance, though, the diver doesn't wear the pump. Getting a pump small enough to be easily/comfortably worn might not provide enough pumping power to circulate the water well.

I think though, that whatever heating element you use would be better served just heating the body directly rather than trying to heat water and then circulate it too. You're doubling your work effort by heating the water. By default, if you're planning on integrating this into a wetsuit, the heating element would heat the water that's against the skin anyway and instead of heating a pumped water system (which would invariably have cold water being input somewhere) you're not "reheating" cold water over and over again. The water will basically stay more or less against the skin and already be warmed by the diver's body and the heating system so it will be more efficient.

 

[Rich Keller]

i am a pretty skinny person, and get cold on dives regularly. I currently use a 5 ml wetsuit with 3/5 hooded vest underneath. I was thinking that maybe some sort of electronic heating system might be a good lower caliber project, that i may be able to do on the side of another project.

Here is what i was thinking:

A rash guard top and bottom stitched together with flat rubber tubes running over the whole thing. This then get stitched in the inside of a thin shorty wetsuit/skin to hold the tubing in place. The inlet(s) and outlet(s) are then connected to an electric pump and to a heating element, so that the water is heated before each circulation. Its kind of like one of those water circulation cooling suits worn under space suits and by fire fighters, but instead of cooling the water, you heat the water. This unit can be worn under my regular wetsuit (i have plenty of room to fill in the torso area). I could carry the electronics in a pouch type weight belt (i use an integrated weight bc).

Is this a ridiculous idea, or is it feasible?

Hot water suits are not new, they have been used in commercial diving for decades with the hot water coming to the diver through his umbilical. Are you talking about this as a self contained unit with no tie to the surface?

 

[bshey]

yeah. what gph/gpm flow would make the unit worthwhile and would it need to have any significant pressure? what could i use as a heating element?

---------- Post Merged at 04:01 PM ---------- Previous Post was at 03:47 PM ----------

or could i just draw in ambient water, heat it, an expel it into the suit?

 

[lucca brassi]

Build 1500 lumen dive light with a focus able beam, 10 hour run time and that weighs less than five pounds. Make it have swap able batteries. It needs to charge from boat power in less than an hour. Good luck sir.

that's not problem at all ;-))

 

[bshey]

ok so here is what i have some up with for a frame/hull/chassis/whatever you want to call it in google sketchup. I am not sire i like how it looks. Its a little boxy for me. I may add some foam which i can shape into some attractive curves and help streamline the thing a bit. In terms of scale, This thing is probably about 6-8 ft long and the diver kneels and sits on top in a relatively upright position. The back if flat, because there is going to be a motor shaft sticking out with a prop.

Let me know what you guys think...




By the way, what could i use for a prop? I am planning to use a 36 or 48 volt 1000 watt brushed electric scooter motor that spins at 3000 rpm. I was thinking a 15-17 inch rc airplane prop (maybe 2 stacked on top of each other) but it would sure be nice to use a marine propellor...

I might still go with 2 trolling motors. Haven't decided yet...