dave wrote: > On Sun, 2011-06-05 at 20:53 -0500, Jon Elson wrote: > >> Well, what frequency of oscillation was it? Really fast buzzing or slow >> rocking back and forth? >> That might give some hints whether it is compensation or not. >> > 1 sec period and about 180 degrees of shaft rotation; just an estimate > not a quantitative measurement. > WOW, that's really slow! I think the servo is OVER-compensated, by a huge amount. The problems I get are in the 20 - 40 Hz range, and may be complicated by belt flap and torsional spring in the leadscrew. Hmmm, I wonder if there is a big cap in the servo amp on the tach input, and it assumes a really low output impedance from the tach? If you were to use a miniature tach with a higher impedance, it would slow down the tach's response, and would make the loop untunable.
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