>
> > One obvious thing to check is mechanical resonance issues.
> > Change the rotational mass of your stepper motor.  Add a shaft ring or
> > similar.  Then check to see if the noisy sections of the RPM curve have
> > changed.  See if your waveform issues have changed.
> > 99guspuppet
> >
>
> Unfortunately, I don't have easy access to extra random mechanical parts
> since I'm 2000 miles from where the mechanical hardware was designed and
> built, but I did try applying friction to the motor shaft with 2 fingers.
>  The extra frictional load brought the current waveform a great deal clos=
er
> to a sine wave, mostly removing the second peak, but I had to nearly stal=
l
> the motor in order to produce the cleaner waveform.  Of course, adding a
> frictional load is simply adding mechanical damping.  Increasing the moto=
r
> shaft's moment of inertia as you suggest should produce a frequency shift
> of
> the mechanical response, correct?  I will try to find someplace local whe=
re
> I can get a part to add on to the shaft.
>
> Thanks,
> Jim
>
>
As a crude but effective way to add some additional mass to the shaft,
consider a roll of electrical tape. If you're feeling adventurous, add a fe=
w
screws in between the layers as you wrap it on to add mass. Yeah, it's kind=
a
fussy, but 20 minutes and a $1 roll of tape is better than waiting for a
McMaster order. (recall that rotational inertia of a disk is a product of
the radius squared, so get the mass as far out as possible for max effect)

If you tell us where you're located, we might be able to offer likely local
alternatives as well.

I do have one other question though - Why'd you decide to add an external
DAC, rather than using and filtering the PWM from the PIC? Granted there's
an update rate limit imposed by the necessary filtering, but I can't believ=
e
that would be worse than the limit imposed by the I2C bus updates.

-Denny
--=20
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