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

[Mike]

I have a jetboat that has a 12v DC motor to move the forward and
reverse bucket. The bucket is controlled by a switch on the front
panel and pushing the switch down moves the bucket on the jet unit
down and so directing the water flow forwards hence making the boat go
backwards. Activating the switch the other direction moves the bucket
up and so the boat goes in the f/w direction. All very simple but it
gives poor position control of where the bucket may be - the longer
you leave your finger on the switch the further the bucket travels.
The bucket is controlled by a 12v DC motor (15 amps) on a worm drive
with end stop switches. Does anyone know of a position control system
that could be used in such a system - the manufacturer's name? I
would probably have to fit a position sensor on the motor assembly and
obviously a position sensor on a lever for the driver. Something
reliable and a stable control loop. Any suggestions?

 

[ron doctors]

I have a jetboat that has a 12v DC motor to move the forward and
reverse bucket. The bucket is controlled by a switch on the front
panel and pushing the switch down moves the bucket on the jet unit
down and so directing the water flow forwards hence making the boat go
backwards. Activating the switch the other direction moves the bucket
up and so the boat goes in the f/w direction. All very simple but it
gives poor position control of where the bucket may be - the longer
you leave your finger on the switch the further the bucket travels.
The bucket is controlled by a 12v DC motor (15 amps) on a worm drive
with end stop switches. Does anyone know of a position control system
that could be used in such a system - the manufacturer's name? I
would probably have to fit a position sensor on the motor assembly and
obviously a position sensor on a lever for the driver. Something
reliable and a stable control loop. Any suggestions?

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.

 

[CWatters]

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

 

[ron doctors]

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

 

[CWatters]

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!

 

[Mike]

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

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.

 

[CWatters]

..

I could design one myself - really just "cook book" stuff but getting
the control loop stable would be take a little mucking around.

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).

 

[Vlad]

Old rotors, use a linear potentiometer to monitor the antenna position
and measure the voltage across one side of the potentiometer and the
center pin.
Latest satellite dishes indicators use a read relay triggered by a
rotating magnet that sends one pulse per revolution. You must sense
the direction of the rotating shaft and convert the number of pulse
into a position.
Vlad

Vlad