Thank you Anthony,
I've now got to decide how I intend controlling the thrusters, turn on lights, cameras etc.
My inital thoughts are a USB gamepad into a small PC, maybe an SBC, Atom type board with a simple GUI (all at the surface), then an RS485 link to the ROV. I have been thinking about possibly using one of those Raspberry PI boards at the surface too as I'm into my retro computing, specifically BBC Micros, or maybe even a BBC micro
8 bit computers still rock
On the ROV there'll then be an oil filled box with a compliant lid (which can be used as a basic compensator) and a pressure tolerant PCB, taking the comms from the surface and distributing it to the thrusters etc on either an analogue output (maybe PWM into a capacitor .... but SPI or I2C DACs aren't that expensive these days) for speed, and a digital control for direction, or maybe just mutliple TTL RS232 links to each thruster.
Lots to think about and do .... time will tell I suppose.
Oh and six sets of thruster components to make and assemble, as well as decide how I'm gonna do the lights and camera and frame and buoyancy and tether