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

Discussion in 'Electronic Equipment' started by Mike, Feb 26, 2004.

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  1. Mike

    Mike Guest

    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?
     
  2. ron doctors

    ron doctors Guest

    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.
     
  3. CWatters

    CWatters Guest

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

    ron doctors Guest

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

    CWatters Guest

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

    Mike Guest

    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.
     
  7. CWatters

    CWatters Guest

    ..
    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).
     
  8. Vlad

    Vlad Guest

    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
     
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