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Choose the correct controller for the correct motor

Discussion in 'Motors' started by John Sapnas, May 4, 2020.

  1. John Sapnas


    May 3, 2020
    Likes Received:
    Hi friends,

    I'm new to electric motors and controllers and I would like to choose the correct motor/controller combo.
    I want to built a continuous motion camera slider for timelapsing. Not a shoot-move-shoot one because I want the camera to record the correct amount of motion blur.

    So I plan to use 4 x 500mm V-Slot 2060 extrusions to get a 2 meter collapsible slider.
    My idea for easy and tool-free assembling in the field, is to fit 5x10mm cylindrical N52 neodymium magnets, 100,5mm deep in the 5mm round holes of the V-slot rails, for both sides of every 500mm piece, and use machined 5x200mm steel rods, which will attract the V-slot rails to stay connected.
    I guess that If my gantry plate has for example 200mm width then the actual maximum distance from start to end should be 1800mm...

    So I found a 3-12v DC brushed geared motor which gives 60 RPM at 12V.
    Precision Spur Gear Motor 60 RPM

    My Idea is to place the motor on the gantry plate and use a 3 inch precision wheel with rubber grip against the rail, in order to avoid time consuming assembling with belts, pulleys etc during operation in the field.
    Lets say that the camera gear is under 2Kg and I don't plan to place the slider in any uphill angle over 30 degrees, which would stress the grip of the wheel on the slider too much.

    So I did some quick math and I found that theoretically when the motor works at its 100% with the 3 inch wheel, I would get 239,27 mm/sec of maximum linear velocity, more than satisfying for real time video which I also need for my projects.

    Now what I would like to find out is how to fine control the motor for very slow speeds, assuming that the motor has a linear behavior against the input voltage.
    If I have understood, with a PWM controller there are 3 factors which affect the speed of this motor, the output frequency, the duty cycle (width of the pulse), and the pulse amplitude (voltage). Correct? Did I say anything stupid? :ROFL:

    What I initially didn't understand is how I can determine the suitable frequency range for a particular motor... Is this the right question?? :banghead:
    I learned about the motor time constant, and that theoretically, I should know this value for the motor I choose, in order to determine the lowest frequency that would produce smooth enough rotation.
    But which frequency should be considered high enough to operate the motor at full speed?

    I looked around for such PWM controllers with LCD displays and I found that many of them allow the operator to set the speed of the motor by altering the frequency and the duty cycle in increments of 1% for both values.

    One more question is if I need a very slow speed, and I set my hypothetical controller to very low values, of amplitude, frequency, and duty cycle, then such a motor would have sufficient torque to drive the gantry plate loaded with 2kg camera gear in (lets say) 15 degrees uphill slope?

    I have created a Microsoft Excel sheet with some calculations based to what I have understood, in order to calculate the possible controller settings for the desired results. You could probably check it to verify if my assumptions are correct.

    So if finally I didn't follow the most stupid approach, does anyone know of a PWM speed controller with LCD display and 3 simple knobs for this scenario, available in EU?
    Are there any alternatives to achieve such slow continuous motion with no belts, pulleys and lead screws?

    I know this is a big post, asking too much from the experts... :rolleyes::zipit::banghead::cry:

    Thank you so much for your help and I hope I didn't post in the wrong forum... :)

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