Hello Ruben,
Cool idea! Every time I come back from vacation I start designing one of these. I am yet to get beyond the back-of-a-napkin-sketch phase...
To start, have a look at this ROV (no affiliation with them and haven't used the product myself).
I believe your main challenges are outside of the control schematics / software:
- Creating a sufficiently water-tight setup that you can drop down to 60-80 feet. At depth (pressure) you can't get away with splash-rated electricals. Things get large/heavy/expensive very quickly;
I wonder if any of the quad-copter projects out there cannot be used a a starting point when it comes to schematics / software:
- Use a 3-axis accelerometer to determine orientation (mainly for horizontal plane reference);
- Use a 3-axis gyro to determine rate of rotation (propulsion control keep those to a minimum when there is no operator input for camera PoV stabilization);
- Use pressure sensor for current depth detection. Delta registration is probably more important than absolute value;
- Use a pressure cylinder with a step motor for buoyancy control (several other ways to achieve this);
- Hook-up each of your motor pods through a decent bi-directional speed controller;
- Your "hover" algorithm will depend heavily on your thruster layout, but the basic idea should be to work towards zero-readings on the gyro and zero-deltas on the accelerometer. Once you get that, it should be relatively easy to "temporarily break" your hover algorithm to move in the right direction.
Just my 2 cents.
Keep us posted on the progress - really looking forward to seeing some underwater footage
Chris