Re: Adjust CP4 Clock Frequency

Ray Gralak


Nothing indicates an error in mount clock rate.

As I said before the tracking rate errors you are seeing in the APCC version you are using are almost certainly caused by unmodeled pointing errors in your truss tube OTA. There is a solution coming using a combination of temperature modeled pointing terms and machine learning.

No matter what the temperature is .. a warm summer night or a cold winter night .. the tracking
corrections are always the same.
Refraction and flexure changes caused by temperature don't affect tracking? I suppose your focus never shifts either with temperature?

Why don't we take this offline?

-Ray Gralak
Author of APCC (Astro-Physics Command Center):
Author of PEMPro V3:
Author of Astro-Physics V2 ASCOM Driver:

-----Original Message-----
From: [] On Behalf Of Craig Young
Sent: Tuesday, May 5, 2020 7:08 PM
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

ATrack monitors a science images folder for new images recorded by the camera. New images are added by
Voyager/MaximDL. When a new image is detected ATrack does a plate solve and measure both drift (difference
between last image and this image) and shift (difference between a reference position or image and this image).
The drift is then used to adjust the tracking rate, the shift is used to temporarily change the motor speed for a
period of time to recenter the next image. Through an observing run of several hours ATrack will change the
tracking rate (RA, DEC) to minimize the drift rate and keep the image centered. It does this very accurately.
ATrack does not care what the cause of the drift, it simply measures it and readjusts the motor speeds to cancel it.
Through the night the changes are very small and consistent .. there is no wild jumps. It is also very repeatable,
from night to night. No matter what the temperature is .. a warm summer night or a cold winter night .. the tracking
corrections are always the same.

Now, if I turn off tracking correction on ATrack and turn on tracking correction in APCC then the stars drift away
very quickly .. pixels per minute .. about 1 arc sec a minute. This happens whether I use a 25 point model or a 200
point model. When I compare the correction rates in APCC with ATrack I see the same difference no matter
where I am pointed. East side or West side. The mount is always tracking in RA too fast and has to be slowed
down. This is consistent with ATrack which always shows the mount tracking too fast and it uses correction
values that are negative .. in other words, it tries to slow down the sidereal tracking rate.

The fact that DEC is similar would seem to indicate there is a base constant in the motor speeds that is incorrect.
DEC is always a positive number in the range 0.02000 to 0.01200 arcsec/sec and is the same in both East and
West sides.


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