I'm trying to control the speed of this motor, with this motor driver and pic16f690.

pwm in my program

5 kHz frequency (0.2 ms period)

Starting with 50% duty cycle the motor doesn't run. But moving from say, 80% to 50% (i.e. program my PIC with 80% duty cycle, and then re-program it with 50%), the motor will run at 50% (of course at a lower speed). I consider this funny. Anyone to explain this?

my motor powered by 5V.


1 Answer 1


If you're saying that it always starts with 80% PWM, but never with 50%, but it runs with 50% after starting, then you're just starting to learn the joys of working with a system that has significant stiction (AKA starting friction).

Somewhere buried in this document is a description, along with some prescriptions of how to deal with it in a closed-loop control system: http://wescottdesign.com/articles/Friction/friction.pdf

  • $\begingroup$ yeah! that's what I mean. thanks for the document. $\endgroup$
    – user1733
    Jul 31, 2013 at 9:32

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