Stepper motor 101 was Re: Are steppers considered low frequency motors?

I've seen those traces before and I think they look awful. "Square"
step motors are optimized to produce torque that is the vector sum of
both phase currents.

The goal from a drive standpoint is to have this torque vector
magnitude be a constant. This means torque is independent of motor
position (on a full-step location or in between) and the motor turns
smoothly.

The only function that does that is sine and cosine (sqrt(sin^2 +
cos^2) = 1) which is why microstepping performance is optimal if the
winding currents are accurate sinusoids.

I was going to post to the files section a 'scope current-probe pic
gif file but it seems I can't do that here.

Mariss


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Alan Marconett" <KM6VV@...>
wrote:

>
> Hi,
>
> So what about Linistepper?
>
> http://techref.massmind.org/techref/io/stepper/linistep/index.htm
>
> Appears to be an attempt to do a linear ramp (triangle?) to drive a

stepper?

>
> Alright, it's got a PIC on it (I like that), but I see two BIG

resistors,

> for a unipolar driver.
>
> If we really want a sine wave, why don't we just use a linear amp

and drive

> it with a sine wave? Class A (B? even C?...) Wastes too much

power I'll

> bet.
>
> Alan KM6VV
>
> > ballendo:
> > In half-stepping we do a little better job of approximating the

sine

> > wave, because we turn one OR two coils on at a time. This puts
> > a "step" in the simulated sine wave, so it looks a little more

like a

> > complete sine wave. (Very little actually in appearance; but

quite a

> > bit better in performance)
> >
> > Microstepping is simply adding more and more "levels" of

definition

> > to the simulated sine waves that all stepper drivers use to create
> > discrete steps of movement from these motors. And as the simulated
> > sine wave gets better; so does motor performance at slow speeds.
> >
>