Well, it's been a while but I've finally got a bit of news to share regarding my new ROV thruster design.
Over the winter I've been doing some re-design on the pressure tolerant brushless DC motor controller. I now have RS232 (TTL) coming out of the PCB and a couple of new tantalum capacitors on there. Unfortuantley the capacitors cost nearly 10 pounds (UK) each! in small quantities. You can't use (cheap, relatively) electolytics if you want a pressure tolerant design unfortunately.
I've also bought 6 brand spanking new motors from Anaheim Automation in the US.
Not cheap but cracking little motors. I've managed to flood my old thruster design a few times and they just keep on working and they're quite powerful for their size and rpm.
I've just been doing some tests with the thruster again, but in the reverse (to the one I tried before) direction and I'm getting a bit more thrust out of it. I saw 1.3kg (divided by two again to give 650g) at one point.
Here's a picture of the setup I used and the new control PCB I prototyped recently, with a potentiometer for the speed, a switch for the direction and level translator for the RS232 so I can use it with my PC.
I am now going to concentrate on getting a kort nozel on there to see if I can get a bit more thrust out of it. I may also make a prop shaft extender because I don't really want to drill holes in my new motor shafts and connect the prop directly to it, which I have done with the old motor.