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Old Mar 22, 2014, 09:23 PM
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derp express's Avatar
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Looking for feedback on ROV plans

Hey all,

I'm a long time aircraft FPV nerd looking to build an ROV to explore the other side. I have a decent amount of experience building / fabricating my own equipment, except I've never done anything that needs to be made watertight, so this project is going to be a real challenge for me. I have some initial thoughts on how I want to do things, but I'd like to get some feedback from you guys since you're the experts. Here goes:

- I'm planning to make the hull out of a single large segment of PVC, with outlying thruster pods that will probably be 3d-printed. My idea is to have everything sealed shut permanently, except a clear front disc that will be bolted onto an O-ring.
Question: Does caulking work for permanent seals between joints, and for wires?

-For the thrusters and servos both, I'm planning to use magnetic coupling to ensure that I don't have to seal moving parts like drive shafts.
Question: Is magnetic coupling an effective transmission mechanism for underwater vehicles?

-For FPV and Control signals, I plan to tow a 30-40 ft wire connected to a surface buoy in order to increase my horizontal range away from the control station.
Question: will the resistance of a 40-ft wire against 5v or 12v of DC be too much for an effective signal?

Finally, I'm entirely unsure as to how I'll go about doing buoyancy control - whether it will be static, dynamic, or some combination of the two. Does anybody know of a simple way to do static control in order to get started?


Any inputs would be tremendously helpful, since my knowledge in the area of submersibles is very limited.

Thanks!

-DE
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Old May 18, 2014, 12:34 PM
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Joined Mar 2012
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Hi, welcome to the world of ROVs. I'm not much of an expert, but have built my own and learned a lot, mostly from expensive failures Anyway I'll try to give a few tips.

Waterproofing is one of the big problems. You may think something is watertight, but go down a few meters and pressure will ensure that if there's an opening the water will find it. Good o-rings are the most effective thing I've found yet, but I'm experimenting with silicone compounds as well. For permanent joints PVC glue is perfectly adequate if applied evenly and correctly.

Great inroads have been made into using magnetic couplings. They certainly have advantages, but you have to fabricate them yourself and using them won't make anything particularly less complex. Most amateur ROVs use waterproof motors, particularly motors from bilge pumps. They are inexpensive and easily hacked and adapted. Servos (should you need external ones) are easily potted anyway.
I would advise against trying things with buoys, rc boats etc. 40' is pretty short as it is when it comes to ROV tethering, and in any case the further away from you the ROV is the more difficult it becomes to control, retrieval becomes more difficult and the chances of the tether tangling on an underwater obstruction greater. If you want to go further out, a boat is the best option. Signal transmission is in itself not particularly difficult over quite long cable lengths provided you have a decent setup.

The buoyancy of ROV's is usually very slightly positive or dead neutral and in all cases static. This for two reasons. First it is far, far simpler, and therefore energy efficient. Secondly it's totally unnecessary anyway. Raise and lower the ROV with vertical thrusters

For tech tips, designs and more head over to the homebuiltrovs.com site.

It's also very much worth getting a copy of The ROV Manual
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