Using a PWM input to control multiple DC motors

Discussion in 'Digital Circuit Design' started by JAnderson94, Jan 2, 2017.

  1. JAnderson94

    Thread Starter New Member

    Jan 2, 2017
    Hey guys,
    This is my first time posting on here, been lurking on and off for a few months on this great site. My electrical experience is pretty basic and I'm looking for new and challenging projects to keep myself busy. Here is my latest idea I would like to try...

    I have a PWM signal supply and I'm looking at running 4 electric DC weatherproof rated motors. They will run around 55rpm consistently for up to 12 hours a day outdoors. I have read some on 555 timers and mosfets but am not really sure where I need to start searching. The kicker is that each motor will have a slightly different load on it, anywhere from 7-15ft. lbs. and they all have to run EXACTLY the same speed. I'm assuming that I will need to find someway to run a tach on each motor connected to a controller that will let each individual motor make adjustments to run at the speed the PWM is calling for. Any help would be appreciated!
  2. MaxHeadRoom


    Jul 18, 2013
    It will be no mean feat to run motors with varying loads at constant speeds, it usually requires some PID feedback system.
    I have used a Galil motion card to do this as it has the ability for electronic gearing, one master and up to 7 slaves off of the one motor, each has to have an encoder.
    I assume you intend either DC motors or BLDC, I have used the A-M-C drives in conjunction with the Galil card.
  3. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    Too bad you didn't yell earlier. These are synchronous motors, but not available at 55 RPM and not weatherproof. Frequency controls the speed. Another bad part is that they are 120 VAC. I did, however make a variable speed control for a telescope inexpensively. I just gave the schematic to someone who needed it and it worked like a champ.

    PWM may control speed, but do you also need braking? You would need a PWM controller for each motor and feedback from an analog encoder or digital one. Digitals come in incremental and absolute. You have to know whether position is important too. Coasting can change the position.

    You can get CW, CCW, brake and coast from some controllers.

    This may be more complex than you anticipated.
  4. MaxHeadRoom


    Jul 18, 2013
    If you are on a budget, you can get some of the Legacy Galil controllers on ebay, either PC slot or stand-alone.
    The control is all servo loop, so electronic gearing sync's up to 8 motors completely.
    Some of the many applications have been flight simulators etc.
  5. dannyf

    Well-Known Member

    Sep 13, 2015
    It is difficult but conceivable to use one pmw signal to control multiple motors.

    It is down right impossible to use input signal, no matter how many of them you may have, to control any number of motors.
  6. MaxHeadRoom


    Jul 18, 2013
    That is a little misleading as in the case of electronic gearing, one input to a master with geared slaves off the master will achieve it.
    I have done it.