Doc G. wrote:
>Each slot of the encoder wheel actually correcponds to 0.3 arc seconds of
>motion
>of the OTA.

In my 8" it's 1.33 arcsec/slot.


>.....However, since there is at least 15 arcseconds of lash in the dec
>gear train,
>even a few slots of jitter does not actually transmit through the
>gear train as OTA motion.


Ah HAH!! An excellent point! I should have thought of that. So it's just
the vibration of the motor going through the motor-assembly mounting, or getting
into the worm by mechanical short-circuit around the gear box. The extent of
vibration of the image that was described would be unacceptable to me. I wonder
what the problem in that scope is. Seems like either there's a helluva lot of
energy in that buzz (possibly some feedback fault, but that seems unlikely - it
would probably sound like an engraver or something if it had that much
energy) or
there's some weird vibrational coupling that makes the mechanics in that
particular mount hypersensitive to normal amounts of servo-feedback "hunting".
It's a weird one.

One of the weird things I noticed on the 16" is that there's a
rubber gasket between the dec motor-assembly and the fork arm into which it
screws. (a gasket like that is not present on my 8-inch). I have no idea why
they put that in there...but maybe a real thin (surgical glove thin, even)
rubber gasket would isolate the buzz vibration...unless it's going right into
the worm. Weird. (Glad it's not MY 'scope! ;-)


Rob Preston
Pgh PA

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