Re: Re: Stepper resonance - not a problem

----- Original Message -----
From: <beer@...>

> If the motor stopped on a particular half-position step as a result of
> insufficient torque, it may not move on the next "full" step either.

Hi Alen,

If thats the case, it probly wouldn't work in full step mode either. What I
was trying to say was that if it had insufficant torque to move to the half
step position, on the next full step - it would go from one full step to the
next just as if it was full stepping to begin with.

> The constant torque "secret" is to increase the current to the winding,
> when only one winding is on. Appropriately scaled, this will result in
> constant motor torque for each position.
>
> The theory is clear and well understood. For any given angle, the
> current relationship should be sin(a) cos(b). For simple half-step, this
> translates to increasing the current by 40% when only a single winding
> is on.
>

I had thought about doing this, my controller has the capability to adjust
the current sense reference voltage from 50 - 100%, with a resistor change
it could do 60/100. But are the motors ratings limited by the temprature
rise - or core saturation?

> Note that at no time does the current through the windings exceed the
> current in the both windings on position, so no motor overheating
> should result. ( Your 4 amp steppers, for example, will have 8 amps
> total in "both windings on" position and 5.6 amps though one winding
> only in the "half" step position ) If the motor is stopped in the
> one-winding on position, though, the motor current must be reduced, or
> the winding will overheat.

My controller does a power saver function where the current is reduced
automaticaly if it has nor recieved a step pulse in 1 second - it resumes
full power imediatly when a step pulse arrives.

>
> I've been working with DanM on this for a bit, and Dan has found that
> going to quarter step solves almost all resonance problems, and that
> going finer than that, to so-called microstepping is really not
> necessary.
>
This is the second time If seen 1/4 stepping mentioned - could you explain
how this works? Do you have to be able to set different current levels
simultaniously when two coils are energized?

Joel