Mini underwater robot (casing ideas?)

This idea is in the preliminary stage at the moment, I have a good level of understanding of all idea's implementation but I need some help with the casing (and battery). Without giving too much away (wouldn’t want to spoil the instructable surprise now, would we?!); basically it’s an underwater BEAM bot, it’s mainly static but it has some "flailing" arms that can move around in an interesting fashion. Said arms can wiggle in two dimensions (above and below the plane at which they are detached - think elbow that can bend back and forwards) and are composed of a levered magnet/coil combo. The entire thing will probably have three arms, all on the same plane. I also need a small rechargeable/replaceable power supply, emphasis on small (the project needs to be somewhere near neutrally buoyant), and some way of recharging/replacing it. Any ideas would be most welcome. Now, since I’m using electronics underwater I want to make sure water cannot get in; problem is I don’t know how. I have had some ideas about some sort of thin sealed plastic, i.e. two pieces of plastic cut to shape and sealed around the edges, but then charging becomes an issue. Plastic would otherwise be ideal. Please keep in mind that I’m a student and cannot afford anything more expensive than a good lunch. Finally, would this make good instructable material? I’m hoping to have a design no more complex than a basic beam bot, as it is at the moment the part count is very low... Thanks

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KentsOkay9 years ago
You can use PVC pipe for the casing. A 4-inch pipe for the center with smaller diameter pipes surrounding it. Just go to your local home center's plumbing section. There all your pipe dreams will become a reality...
andy (author)  KentsOkay9 years ago
It’s a good idea and would work fine if I were using a propeller or set thereof, but the problems of sealing the moving parts remain. To elaborate; it consists of 1x 20 pin chip, 4 capacitors and 4 resistors of negligible size a coil and a couple of magnets, both the size (roughly) of a 2 pence coin, then a few compact mechanical parts of small size to operate the up down motion of the "appendages". Main idea so far is to also have a couple of solar panels (thanks to westfw for that idea) and a 1 farad cap (one of the teeny tiny ones) with a solar engine, just have it run in short bursts. Sealing ideas; at the moment are getting two sheets of plastic (Like the flexible a4 plastic sleeve material, the flexible transparent ones)sandwiching the device between them and running my soldering iron round the edge with a mild insulator (so as not to actually burn the plastic). Tests in this have been mixed; need more plastic sleeves and experimentation. I may then cover the whole thing (either the inner parts or the outside or both) with an insoluble/waterproof grease of some description. It will sit in an otherwise empty water container, so no toxicity worries on that score, but obviously the more eco friendly the happier I am. Any more suggestions as to casings, plus any problems you spot in my design would be most welcome, thanks, Andy
have you thought about using water pumps for propulsion?
andy (author)  frank260801159 years ago
No not really, pumps are complex power hungry and big, I need small light weight and increadably cheap, which is what the current design is... but its hard to seal, I may have to swithch to using a number of propellers and motors if the design doesnt work out, thanks for the input though! Andy
here's a thought you are making a sub, if the hole is below all the air inside the boat, even if it is not sealed, no water should rush in, because air is less dense than water or simply wrap the motor shaft in teflon tape :-)
andy (author)  frank260801159 years ago
thanks, yeah, I`ll look in to it, I will be beginning testing/construction next week when I have time off and all the parts ready. If all goes well I`ll make another, documenting the process and implementing any corrections/modifications based on the first build. Thanks for the input, much appreciated, Andy
westfw9 years ago
My brother made an underwater habitat for a mouse back in the days of grade-school science fairs. Sealing things to make them waterproof is a lot harder than you think. There's always solar power for charging your batteries, even if it takes a long time. Magnetic reed switch for on/off...
andy (author)  westfw9 years ago
Yeah, sounds good... though I simply need to keep metal and water separate... perhaps wax/grease? Or a flexible silicon gel? The flail arms can be made of plastic and so the frame would only have to tolerate about 1mm of torsion movement (maximum) and stay waterproof. I thought maybe I could use EM induction for charging, as it already uses a large coil for movement, perhaps a reed switch connecting it to a rectifier? Solar panel would be good, but I think I would have to use a solar engine with it, and bursts would typically last 5-10 seconds, with maybe a minute charge time, which isn`t the best but it is acceptable if the alternative is corroded terminals poking out of it. Thanks for your advice, Andy