Problem with meridian flip #Mach2GTO #APCC

David Johnson

This concerns the Mach2GTO.  I'm in the northern hemisphere.  I woke up this morning, and I found out that I didn't get any data after my target passed the meridian.  Sequence Generator Pro told me that there was an error when trying to do a meridian flip, and SGP aborted the sequence, although the mount went happily along.  I did have the meridian limits set, but for the declination it was pointing to, it continued (safely) to go counterweight up without hitting the meridian limit, and that's how I found it this morning (very CW up).  I want to emphasize that I have not had this problem before, despite doing dozens, if not hundreds, of automatic meridian flips with my Mach2.  I'm going to wake up tonight and see what happens when it tries to do a meridian flip.  Meanwhile, I do have a theory on what may be the problem.  For the first time with Mach2, I'm using a camera-lens system and not an OTA.  I probably don't really need to do APPM at this scale (~23 arcseconds/pixel), but I wanted to try it and see what happens.  It mapped fine after some tweaking.  However, the error when the mount is pointing to the west was huge.  This is probably due to the fact that the lens system had a lot of cone error, given the way it's mounted.  I'll try to work on issue this tonight, but, due to the mounting system, I'll probably always have some significant cone error. 

However, it got me to wondering about what happens if SGP asks for the meridian flip, and the mount thinks, due to correction from APPM, that after the flip, the mount would actually stay on the same side as before the flip.  In other words, after the flip, the camera system would point to west of the meridian, but the mount would point to the east, due to the cone error and the correction of it for points west of the meridian.  Maybe then, the mount would not do a meridian flip, as requested by SGP?  This might be the problem I had last night.  An obvious solution is to delay the flip until the mount and camera system would both be pointing to the west, assuming it's safe, which it would be in my case.  

Anyway, I saw an extreme example last night, but it seems like this could happen with smaller cone errors and might be an issue.  The bottom line question is, what happens if software asks for a meridian flip, and, due to APPM correction, the mount (not the optical system) would still point to the east, after the meridian flip, due to cone error.  Would the mount still flip?

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