Slew and Center causes AP1100 to oscillate across meridian

Twice now I’ve had an issue with SGP slewing my scope across the meridian back and forth when trying to center on an object slightly east of the meridian. Now this is probably only a problem with SGP and APCC with an Astro-Physics AP1100 mount that has the meridian limits set. This mount allows the scope to start on the east side with the counterweights up, thus making it unnecessary to do a meridian flip.

However, when the object is close to the safe zone as set by APCC, and the initial slew puts the scope on the east side, if the ‘center here’ fails SGP sends a recenter command to the mount to try again. This time the scope moves to the west side and tries to center. Since the mount has flipped, the ‘center here’ may fail again as the position may still be slightly off target. If the correction needs to be made to the east the scope now flips again, moving to the east, and the process continues - back and forth.

I’ve contacted AP and they seem to think SGP (and other tools) send new coordinates to the mount to make centering corrections rather than an offset to the coordinates. This is (as per AP) likely to be the cause of the oscillations.

Can this be corrected (as a mod to SGP)? The first time this happened my imaging run for the night was ruined - tonight I was at the computer watching the issue and corrected it.

Roland Christen on the AP Forum made the following post to my inquiry on this issue:

There is an interaction between safe zone and slewing within the counterweight up position for centering. It depends how the centering command is done. It can be done two ways, either with a timed move at 1x sidereal or by issuing a new coordinate. If it is done via a timed move, similar to the way guiding software does it, then there is no issue and the mount will move directly to the new position. If it is done via a commanded co-ordinate move, the mount will do a safe slew procedure, which first brings it to a counterweight down position before moving to the new commanded position.

At this time we have no way to distinguish between a commanded goto for centering and one for slewing to a new object. Therefore all commanded moves using coordinate slew methods will cause this back and forth motion, in and out of the safe zone.

The log from this evening is at th following DropBox link: Dropbox - File Deleted



If your Sync Behavior is set to “Sync” in SGP, then the coordinates are not “new”, but the same ones we just sent the mount as that is where we actually want it to go. I don’t really understand the “Safe Zone” or how it’s implemented here. But it seems odd that asking the mount to slew to the same location would result in different behavior.


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