RC reversing dc motor

Discussion in 'The Projects Forum' started by bigmannie, Jun 3, 2008.

  1. bigmannie

    Thread Starter New Member

    Jun 3, 2008
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    Hi,
    I ' looking for a simple (if possible) circuit where I can drive a low voltage geared motor in forward and reverse via remote control, turning about 270 degrees. The problem I have come across is, that by just using limit switches and /or relays, as soon as the motor reaches the limit switch, it changes direction straight away and thus changing the direction on my joystick as well and so you never know which is left or right. I need for the motor to stop at its limit and the only way it can move in the opposite direction is by moving the joystick in the opposite direction.
    Does anybody know how to achieve that?

    Cheers, Mannie
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Yes you can do it. Use two SPDT relays and two limit switches. Connect the motor on the two common (C) pins of the relays, then connect the normally closed (NC) pins of the relays to ground and then connect the normally open (NO) pins of the relays to the positive site of the power supply.

    Now connect one end of relay coils to ground and the other end to your control circuit.

    Finally, connect to each relay a limit switch (use the common and normally closed pins of the limit switch) from the relays normally open pin to the site of the coil which goes to the control circuit.

    Operation:

    when you give the relay an initial signal to operate, it will close its NO pins and stay latched due to the limit switch. Then, when the motor reaches its final position the NC pin of the limit switch will become open and the relay will switch off and your motor will stop. To move your motor to the other site you have to activate the other relay.

    Is that allright or you want it a bit different?
     
  3. mik3

    Senior Member

    Feb 4, 2008
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    I forgot to say that the motor will always be on the left or right position and neither in the center for example unless you turn the power off!!!!

    If you want you can modify it to move the motor by holding all the way to the end your joystick pressed. In this way you can stop it wherever you like and just have the limit switches to detect the final position.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    See the attached schematics.
    The first one is likely what you would have with just the joystick.
    The 2nd one adds limit switches to stop, but not reverse travel at the limits.
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    That is very elegant, Sarge!
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Just something I had kicking around from a few months ago when another poster posed a similar question.

    The next schematic gets quite a bit more hairy; auto-return to center. This is what you have to deal with when using just relays and limit switches. It IS possible, but it gets involved.

    Much easier to do this sort of thing with a uP, and a pot to tell the position of the motor's arm.
     
  7. bigmannie

    Thread Starter New Member

    Jun 3, 2008
    2
    0
    Hi Mik3,
    I think you understand what I'm trying to do. Yes, I must be able to stop the motor at any position by releasing the joystick and the limit switches are only there for the final position. It's just, that your description is a bit confusing to me. Do you think you could draw up a circuit? I would really appreciate it.
    Thank you for your time, Mannie
     
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63

    Check the second circuit SgtWookie posted on post #4 but be careful that your limit switches can pass the motor current without get burned.
     
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