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Limbo time, PWM, DC Motors, and stiction. How slow can you go. — Parallax Forums

Limbo time, PWM, DC Motors, and stiction. How slow can you go.

Peter JakackiPeter Jakacki Posts: 10,193
edited 2010-02-27 19:20 in Propeller 1
As part of my MultiPLC http://forums.parallax.com/showthread.php?p=791643 work I have just been playing with some small DC motors and PWM. Just thought I'd share this short video that shows how slow you can go with a DC motor. By choosing the right frequency for the motor at a certain load and speed you can make it go very slowly and relatively smoothly. I am just using the standard PWM object connected to a pair of transistors in a ULN2803. A general-purpose object for open-loop motor speed would then calculate or lookup the best frequency for a given speed. A closed loop can utilize this method as well. I found with these motors that a range from 5 to 50Hz or so usable with higher frequencies only suitable for higher speeds but without any real advantage. Anyway, I thought some might be interested.

Video (1MB) pbjtech.com/propeller/pwm1.avi

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*Peter*

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-02-27 17:17
    Interesting, what kind of load curve can you ascertain from such slow speeds I wonder?

    When I first read this, the first thing that came to mind was a variable switch-mode power supply which can be an effective and efficient way of controlling DC motor speed, but I don't think you can go as slow as you have achieved using that method.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • DufferDuffer Posts: 374
    edited 2010-02-27 19:20
    Wow, That's even slower than Progress Bars when installing Windows programs. You have to put the mouse pointer at the leading edge to see if it's really moving at all! lol.gif

    Duffer

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    Any technology, sufficiently developed, is indistinguishable from magic.· A.C. Clark(RIP)
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-02-27 19:20
    On the old teletype machines the character selector had to be driven by high volts (80V+) via a resistor to get the time constant (L / R) short enough. I wonder is the same is true for a short PWM pulse into the inductance of the motor.


    Addit Or key on / off a constant current source

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    Style and grace : Nil point

    Post Edited (Toby Seckshund) : 2/27/2010 7:47:57 PM GMT
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