dc motor position control

Discussion in 'Homework Help' started by ayodele234, Sep 1, 2011.

  1. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    the attached diagram is used to control dc motor direction of rotation. if the two
    potentiometer is equal in value the motor will stop rotating.
    My problem is this, if the pots values is below 80% say pot 1=70 and pot 2=70. i expect at this value that the motor should not rotate, but the motor still rotate in both forward and reverse direction.
    Please, anybody with better circuit or who have an ideal on how i can make the two ics ua741 not to give output when the two pots values is the same.
    Thanks for your prompt responses
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    What do you mean by "both forward and backward"? Does it oscillate?
     
  3. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    yes it oscillate.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Yes, use a H-bridge with two upper p-FETs and two lower n-FETs and one switch on each leg.


    What are the potentiometer values?
    Where did you find this circuit?
    Why do they use upper n-FETs ?

    I redrew the circuit without the LEDs and a resistor as load.
     
    Last edited: Sep 1, 2011
  5. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    The value of the potentiometer could be any value provided they are equal in value.

    on the net.

    I believe it will work or any better one i can use.

    Thank you very much for ur response.
     
  6. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    thank you very much, i had simulated the circuit and it worked.
    How can i include LED because it as and indicator when the motor is out of sight.
    Once again thank you.:cool
     
  7. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Wait a second. I didn't do anything, just redrew the circuit. It's the same circuit. Did you build your initial circuit physically or just simulated it?
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    all hail praondevou & his magical redraw skills!
     
    praondevou likes this.
  9. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0

    Sir, kindly the particular upper P-FETs and lower n-FET, i should use.
    Also sir i should i connect it. Thanks
     
  10. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Here you go. Whatever H-bridge you use I still don't know why this should work properly. The Opamps have no feedback, so depending on the voltage difference at the input their outputs go either low or high, i.e. one of the outputs is always high. That means the motor is always powered, in one or the other direction.

    For the H-bridge with p-FETs you can't use the 741 because it's output doesn't go to the power supply voltage, and the p-FET needs it to turn off, so you'd need an Opamp with a rail-to-rail voltage output.

    You still didn't post the reference. Where did you get it from? Can you post a link?
     
  11. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    sorry for not post it earlier. http://www.nelnick.com/motorposition.html. the entire i deal of this project is to detect the position. just like controlling the angle of rudder or something like that. Sir to be sincere i am a beginner in electronic.
    Thanks for all your post.
     
  12. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    The link brings me to a site with a lot of ads... Is that the right link?
     
  13. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    file:///C:/Users/comparq/Desktop/elect/desktop/power%20supply/DC%20Motor%20Reversing%20Circuit_files/Controlled%20electric%20shock.htm.
    Kindly check the above link. thank
     
  14. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    This is not a weblink.
     
  15. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    this is the material it explain what i want to achieve. kindly read through.
     
  16. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Apparently you don't have the feedback described in the pdf you posted. P1 is somehow mecanically coupled to the motor, so whenever you adjust P2, the motor will turn until P1 equals P2.
    I wonder what potentiometer this is, as it has to be one that can make a full turn, otherwise if something goes wrong and the motor continues turning it could damage the potentiometer... :confused:
     
  17. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    please if you have another circuit that can achieve this purpose kindly send and guild me through. I PRAY I WILL BE AN ELECTRONIC GURU LIKE YOU ONE DAY.
     
  18. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    i had installed a limit switch that will protect the potentiometer. The mechanical unit will have to travel long distance before it make even half of the potentiometer. So no confusion.
     
  19. ayodele234

    Thread Starter New Member

    Apr 26, 2011
    20
    0
    hello everybody, assist if you can pls, i still need response to this thread.
     
  20. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Just to make sure, IS one of the potentiometers mecanically coupled to the motor shaft?
     
Loading...