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

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> 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