DC motor control system for reverse bucket position control on a jetboat

If the control arm is not in the water then a simple potentiometer would be the simplest. If it is under water then a magnet with linear hall sensor would be my choice. Once you have the control system working you can make a closed loop system that works by setting the bucket to the required position and the servo loop will do the rest.

You could probably just count revolutions of the screw jack. Reset the counter using the end stop.

I like this idea. You could do it all using CMOS IC's for almost no power drain or cost. ron

I've built some equipment for use outdoors and it's surprising how much decent waterproof connectors can cost in low volumes!

Thanks for these comments. The control arm is not in the water so the position sensing should be relatively easy. Counting the screw rotations is an interesting idea and I will have a close look at the mechanism to see if it could be done that way. Have had a good look around trying to find a manufacturer but nothing seems to jump out at me, particularly for 12V systems. I could design one myself - really just "cook book" stuff but getting the control loop stable would be take a little mucking around. Was hoping for a commercial type for better reliability. You don't want it to fail 30Km up a river somewhere.

Modern digital servos (for model aircraft) do some fancy tricks. Like slowing down the motor as the output approaches the right position to prevent overshoot and oscillation. I guess it all depends how accurate you are trying to get it? (large deadband).