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

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

> >
> >
> > Mariss Freimanis wrote:
> >
> > >That is the point I disagree with. Though a motor may have a +/-

> > >non-accumulative tolerance, it does not mean the steps adjacent

> > >the current one will vary by +/-3%. In practice they vary by

> > >much less than that. The error is cyclic, i.e. over the span of

> > >full revolution, a "wobble" if you will.
> > >
> > >You can easily prove this to yourself. Stand a motor on its end

> > >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

> > >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

> 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
>
> I'm about to pull apart another HP laserJet II for parts, (anybody
> want stuff, free for the shipping costs)
>
> and inside there is the laser mirror. sound like I can grab that

> put it on a NEMA34 and connect that to one of my Gecko's and a
> Xylotex and see how the laser pointer moves on the calibrated chalk
> marks I scratched on the basement wall 30 feet away.
>
> The mirror is simple as it can be easily attached to a timing gear.
>
> I'll be a couple of weeks, but I'll let you know.
>
> Dave