Re: [CAD_CAM_EDM_DRO] Re: stepper vs. servo - Allegro and ignoring the edges....

Mariss Freimanis wrote:

>That is the point I disagree with. Though a motor may have a +/-3%
>non-accumulative tolerance, it does not mean the steps adjacent to
>the current one will vary by +/-3%. In practice they vary by much
>much less than that. The error is cyclic, i.e. over the span of a
>full revolution, a "wobble" if you will.
>
>You can easily prove this to yourself. Stand a motor on its end so
>the shaft is vertical. Superglue a 1/2" by 1/2" mirror sliver to the
>side of the shaft. Use a laser pointer and bounce the beam at a right
>angle from the mirror to a wall about 10' feet away. Mark the
>projected laser spot with a pencil, step the motor and mark the new
>laser spot. Repeat this a few times.
>
>There will be much less than a 1% difference when you measure the
>distance between the pencil marks.
>
>

Hey, a great thing to check when you have such a setup is to see how much
hysteresis "or backlash" there is in a stepper motor. Move CCW one step,
mark, then move CCW and back CW one step each, and see how far off
the mark is. Anybody actually done this and measure it in % of a step?

Jon