“How hard could it be? It turns out that there were several challenges to making a submersible ROV. But it was a fun project and I think it was quite successful. My goal was to have it not cost a fortune, have it easy to drive, and to have a camera to show what it sees underwater. I didn’t like the idea of having a wire dangling from the driver’s controls, and I have a variety of radio control transmitters already, so that’s the direction I went, with the transmitter and control box separate. On the 6 channel transmitter I used, the right stick is used for forward/back and left/right. The left stick is Up/Down and turn Clockwise/CCW. This is the same setup used on quad-copters, etc.
I looked online and saw some pricey ROVs and saw a few with “vectored thrusters”. This means the side thrusters are mounted at 45 degree angles and combine their forces to move the ROV in any direction. I had built a mecanum wheel rover already and I thought the math there would apply. (Ref. Driving Mecanum Wheels Omnidirectional Robots). Separate thrusters are used for diving and surfacing. And “vectored thrusters” sounds cool.
For ease of driving it, I wanted depth hold and heading hold. This way the driver doesn’t have to move the left stick at all except for diving/surfacing or turning to a new heading. Turns out this was also a bit of a challenge.
This Instructable is not intended as a set of directions for doing it yourself. The intent is more to provide a resource that someone might draw from if they intend to build their own submersible ROV.”