the best (cheap) hull material I have come across is metal water pipe, the huge sort they pump water from town to town in. you would have to close off each end but its a good start and round, which means it will be strong.the best way to do buoyancy is to make the craft neutrally buoyant and then push your self down. add two long air tanks at the top, and then add unhappy weight to counter this (just).you now need some air to breath. the best thing to use would be SCUBA tanks. just fill them with air from a compreser and then regulate the airs release. you will need to remove the "stale" air at the same rate that the old air is removed.the best thrust source is an electric motor. I would recommend getting some from old golf carts. you will need to water proof them and add a propeller. put two at the back (forward thrust), two at the front (backward thrust), one either side (left/right thrust), two on top (down thrust), and two on the bottom (up thrust). power them off a golf cart battery would be my advice.to control the motors I would use a set of relays. you could do it like this guy has http://www.homebuiltrovs.com/ (look in the how to section).you could then add alsorts of things like lights, sensors, cameras and manipulator arms.and of course you could paint it yellow.
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Submarines, personal or otherwise, come in 3 varieties:1. Wet - you bring your own scuba rig, you get wet, and you are exposed to ambient pressure. A "swimmer delivery vehicle" is an example.2. Ambient dry - you are in what amounts to a mobile diving bell. The air inside is compressed to the same pressure as the surrounding water; but you are dry, and staying warm is simplified. Leaving the sub while submerged is simpler as is returning to the sub; but depth is limited and surfacing needs to be done at a pace consistent with decompression tables. Ambient dry subs generally stay close to the surface, for safety reasons; but they have the advantage that they can be much lighter, simplifying towing it on a trailer to your dive site, as they rely on air pressure to resist water pressure.3. 1 atmosphere dry (also known as shirt sleeves) - you are dry and pressure in the hull remains consistent with the pressure on the surface. These rely upon the strength of the hull to resist water pressure.Assuming what you have in mind is for carrying one or more human beings, and not as a remotely operated vehicle, large propane tanks have been successfully used as pressure hulls. You will want to calculate volume carefully, and I would recommend you calculate buoyancy using distilled water as your assumed medium, so that you will have enough reserve buoyancy to be able to surface in the event that salinity is lower than you assumed in your calculations. Definitely use drop weights of greater mass than your ballast tanks. Assume a worst case that your ballast tanks are structurally compromised, so that you can still surface. Ditching at depth is not something you want to have to do.
Red Pandas For The Win!
I m in the process of building a submarine myself. I'm out of funds but have a lot of motivation to do it. I have read hundreds of reports online and found out that one of the best and cheapest ways to build a personal Submarine would be to use a Propane tank. Actually you will have to use at least a couple Tanks. I don't believe you will need more that 2 Electric motors to move your submarine. Just put one on each side and make them tilt up a down to move the submarine, left, right, up and down.To turn right you need to put the right motor on reverse and the left motor on forward. I think it would be best to use a Joystick to navigate the submarine.I was thinking about using a water pump to fill the submarine to go down and the same water thank to get rid of the water and resurface. If you are very luck it will cost you around $4500 to $5500 to build a descent Submarine. For oxygen I suggest you use at least 4 to 8 tanks. You should also try to make the cabin as small as possible so you wouldn't need too much air to fill it up. You will need a lot of sensor, oxygen level sensor, carbon sensor, dept indicators, pressures indicator and few more.I have some initial drawings that I m fixing to put on this page. If you have any question please feel free to ask me.http://checkthisup.com/submarine
First off ask any diver about filling your breathing tanks from any old compreser and they will smack you. Most Scuba compreser are have filters and are a better mix of gas that will allow you to live during and after the dive. second not to shoot you in the foot but without some good schooling/engineering you are more likely to build a coffin than a sub. besides with the tech to day you go spend less than 300 and buy yourself a underwater scooter. still need to solve the breathing underwater bit but movment is solved.
A 1 atmosphere submarine is called a boat : )
Hull, buoyancy tank(s), oxygen supply, power for locomotion. If you skimp on #1 or 2, whatever you have for #3 becomes a lifetime supply : P
If you are trying for depth, you need to figure out how to sink-sounds easy, but not if you want to float later with 100% reliability. Most subs use air tanks that get filled with water in order to dive, then get re-filled with compressed air to surface, in an emergency, they have solid ballast to counter the air-space inside and can drop them for emergency surfacing.
A different way is to swim like a fish or dolphin-use power to force the hull under water by 'flying' with small 'wings'. Very power intensive, but possible.
I wasn't referring to the depth the sub could travel, but the continuity of the internal pressurization. Thanks for the info on surfacing though.
a big barrel with a window : )