I'm taking a graduate level autonomous machines course that consists of a completely open ended project to create an autonomous robot that completes a task. The idea I came up with is a submersible vehicle that will drive on the bottom of a kiddy pool (to simulate a mall type fountain) and collect the change from the bottom.
I'm having some issues locating sensors for obstacle avoidance that can sit out in the water -- obviously IR is out of the question, bump switches are only to be used as emergency back-up, so sonar is all that's left. The only sonar unit I can find spec'd for underwater use is $130 and I'm working on a student budget (the board was $100 as it is and motors + motor controllers will already make this project hurt my wallet, hah). I see plenty of sonar units for much much cheaper but I have no idea what on the sensor or connection requires waterproofing.
BTW, the unit will be very small - no more than a 1ft diameter. I've already tested the available tap water on campus and can run DC motors at a low voltage (4.5VDC motor on a 9V battery) without waterproofing (there was a drag issue with the cheapest brushed motor I tested however) so I'm not sure how adverse a reaction other components may have. It also doesn't have to work beyond May, so corrosion isn't a huge factor for me either.
Does anyone here have any experience with development of underwater sensors of any kind or waterproofing devices? As of right now the only idea I have for even sensing the coins is another sonar unit. It seems the miniature UAV community is rather lacking and most devices aren't on such small a scale as my robot. I did some digging and reading through this forum, so I don't think I'm reposting any questions - but sorry if I did.
Regardless, this is a cool little forum! Thanks for any help!