hey weird timing. I was looking at a larger version of that design a few wees back, it looked like it had got itself stuck in a lake amongst some lake-gunk. One thing I'd like to build is an autonomous ROV using gps to chart its way around the shorelines. I think I'd prefer a more efficient design like a tube or classic sub shape, that way less power would be needed for propulsion as these ROV designs don't look very hydrodynamic. You could use relays for switching, I just bought 50 x 5v for 12 bucks off ebay so they're not expensive. Any of the LED examples will power a 5v relay, you just need to hop the 220ohm resistor(s). I've seen a design using a battery powered toothbrush, I pulled one apart the other day and the motors pack quite a punch, and they're already water proof. The larger motors they've got attached to that thing I wouldn't know what they're called, Curvetech Thrusters? They look expensive. Anyway, all very doo'able with Arduino, and then some 