Changing direction for DC motor

Discussion in 'The Projects Forum' started by pickynancy, Apr 16, 2010.

  1. pickynancy

    Thread Starter New Member

    Apr 16, 2010
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    Hi. This is my first post here. I am somewhat of a newbie with electronics. Well, I am working on a project, and I want to build a circuit to reverse the direction of a dc motor. Here is what I want to do...

    The dc motor will be driving a pulley that moves an object on a fixed track. On both ends of the track there will be a switch (of sorts) that when engaged will reverse the direction of the motor, so that the object on the track will constantly be moving back and forth on the track, from one end to the other.

    So, my question is about the circuit itself. Could I use a bistable multivibrator to achieve this? And, if I could, how would I wire the motor to the outputs to achieve this reversal? I am not opposed to the idea of using any other circuit, so any suggestions on how to achieve the change in direction would be great.

    Thank you.
     
  2. russpatterson

    Member

    Feb 1, 2010
    351
    16
    I've seen people use an H-Bridge circuit to drive DC motors (that require reverse). I haven't done it myself but if you Google h-bridge motor control you'll get a bunch of info.
     
  3. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
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    A good old relay may be the best way to accomplish this.
     
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  4. pickynancy

    Thread Starter New Member

    Apr 16, 2010
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    Thanks guys. I think I am going to take both pieces of advice, and use an H-Bridge and a dpdt relay. I don't know too much about relays however, I know the concept, but I never worked with them before.

    Thanks again!
     
  5. pickynancy

    Thread Starter New Member

    Apr 16, 2010
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    Oh, wait...one more question. Since I want to use N.O. type switches, I would use a latching relay, correct? Latching relays only need a pulse to change and stay changed, right? Or am I thinking of something else?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    A dpdt latching relay and two switches to send the pulses to change direction would be the least part count way to do this. You would swap the +/- on each side of the relay. So running one direction, the relay would be conducting - and + after the pulse it would switch to + and -
     
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  7. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    I think using an H-Bridge to just turn on a motor would be overkill, unless you plan on using PWM to drive the motor, 2 DPDT relays and a couple of switches would do what you want to do....


    My .02

    B. Morse
     
  8. pickynancy

    Thread Starter New Member

    Apr 16, 2010
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    Thanks everyone! I got it. :eek:) I'm going to do exactly what you said Retched.


    I'm looking forward to learning from you guys here! Thanks again!
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    That whats great about this place.. You can get a bunch of different soloutions to a problem.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    This is basically what you need:

    [​IMG]

    Except in your case, you don't need S3 and S4 - replace them with a piece of wire.

    Pressing S1 or S2 momentarily will cause the relays to "latch" and the motor to run in that direction, until the other switch is pressed.
     
  11. williamj

    Active Member

    Sep 3, 2009
    180
    32
    Picknancy,

    Depending upon the "size" of your project, you may want to consider utilizing a brake and timer in your circuit. Motors of any kind (especially larger motors) generaly frown upon rapidly switching directions back and forth.

    A brake in your circuit stops the motor and eliminates the torque needed to overcome the momentem of the motor going in a particular direction (which generates excess heat and mechanical stresses) and the timing circuit gives the brake the time needed to acheive this.

    (I hope I said this correctly and it makes sense. :/ )

    williamj
     
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