Re: [CAD_CAM_EDM_DRO] Re: 20 Amp 80 V $99 DC Servodrive

Mariss Freimanis wrote:

> The encoder must be on the motor shaft for loop stability. If it were
> on the pulley, the belt "give" or compliance would certainly exceed
> 0.05 degrees (+/- 1/2 count for a 1000 line encoder) and the loop
> would be impossible to compensate.

Interesting. I have a setup where the encoder is directly driven with a
helical coupling
off the end of the leadscrew. The DC tach is driven by a miniature belt
off the
leadscrew. The (servo) motor drives the leadscrew through a 2.5 : 1
toothed belt
reduction. There may be some very small vibrations due to belt flap and
other
belt/sprocket irregularities, but the loop is quite stable, with not
even the smallest
suggestion of hunting. (I do have one nasty resonance that occasionally
can get
excited in the Y axis, which is a torsional bending of the entire axis
mounting plate.
It is at a much higher frequency (about 800 Hz) than any belt-related
modes.
I think I have finally tuned this one out, too.) I do keep the belt
quite tight.

Jon