Quote:
Originally Posted by Shiraz
I think that one advantage of the direct drive mounts with encoders is that the main feedback loop runs at fairly high speed, so they can react quickly to control the effects of wind gusts - regardless of whether or not they are being guided. A conventional mount does not have an equivalent feedback loop, so you must rely on mount stiffness (or an AO) to deal with wind.
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Yes, that is basically my understanding as well.
There are a few qualifiers however. Irrespective of the power and accuracy of the drive/ encoder assembly, the maximum useful guiding frequency will be a function of the resonant frequency of the telescope structure and the tuning parameters (proportional, integral & derivative) applied in the control algorithm. It is likely to be the case that the factory default settings will be different from optimum settings derived by experiment in the field.
Also, it needs to be said that direct drives are (in theory) able to manage deviations due to such things as wind loading (particularly in the dec axis) at a frequency and accuracy that is simply not possible using a conventional gear train.