Re: fickle y-axis

Peter,

In a word, overshoot.

When a motor takes a step it "rings" or oscillates about the step
location. If your step rate is just right, the subsequent step
catches the motor just as it's beyond the last position (overshoot)
and is now attracted instead of repelled by the new location. This
will occur in either direction.

Mariss


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "forumtvm" <forumtvm@y...>
wrote:

> Hi Jeff, others,
>
> Somehow I still don't understand how my stepper should move in
> undetermined direction when 1 phase B is out. Below is an attempt

to

> show a stepper after phase A had just been activated, in which case
> the rotor would be attracted to the nearest opposite pole. In a

half

> stepping configuration This would would be followed by AB, then -B

in

> which case nothing happen. The next step would be A'- when the pole
> would reverse polarity (in a specific sense determined by the

command)

> ........(A)
> .........N.............
> .......................
> ..B......S........B....
> .........|.............
> .........|.............
> s........x............N(A)
> .........|.............
> .........|.............
> .........|.............
> ...B.....N........B....
> .......................
> .........S.............
>
> The diagram below would show phase A polarity reversed. This would
> show the rotor been moved in a very specific sense, definately not
> indeterminant.
>
> ........(A')
> .........S.............
> .......................
> ..B...<--S........B....
> .........|.............
> .........|.............
> N........x............S(A')
> .........|.............
> .........|.............
> .........|.............
> ...B.....N-->.....B....
> .......................
> .........N.............
>
> Could it be the reason for the erratic behaviour was due to

something

> else?
>
> Anyone had any experience with the wire for 1 phase broken? How did
> the motor behave?
>
> Peter
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "jeffalanp" <xylotex@h...>
> wrote:
> > Hi Peter,
> > Yes, all 100 poles are activated; they are all wound with the
> > same wire.
> > Best bet would be to find a cheap (or broken) stepper motor

and

> > open it up and take it apart (which can ruin it). On a small
> motor,
> > you will see the rotor has two different sections, one slightly
> > offset from the other (A and B). You can also 'see' the 'poles'

on

> > the rotor.
> >
> > Jeff
> > http://www.xylotex.com
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "forumtvm"

<forumtvm@y...>

> > wrote:
> > > Hi,
> > >
> > > Just one small question. In a stepper motor with 100 poles for
> > phase
> > > A and 100 poles for phase B, when say phase A is activated,

does

> > all
> > > the 100 poles get magnetised. I suspect this is the key I need

to

> > > grasp before I get to understand why my y-axis got to behave so
> > > erratically when one wire got loose/disconnected.
> > >
> > > Peter