DIY Scope Controller - SyncToCoordinates

Greetings,

having upgraded to ACP8 from ACP6, the very first image of the night of course yields a SyncToCoordinates from ACP as I still have few correction points in ACP's pointing corrector. But the odd thing is that most often after ACP receives the pointing error from Maxim, instead of slewing to the original intended target, it slews to the very same coordinates the scope has been told to sync to, thus the scope moves not at all, and the image is of course still off from the original one. Then ACP slews to the original intended target. Odd because this only seems to occur perhaps 80% of the time (beyond maximum error?). More problematic is that the offset occurs night after night, of the same magnitude (0.3 deg in RA). I had no such issue with ACP6.

My setup is a DIY, the Dec and RA axis are 17 bit absolute encoder, so the HA and Dec of course never drift. I am using current sidereal correction which yield topocentric scope coordinates. I ask because the 0.3 deg is just about the time between the image was taken and the sync is issued. I would have thought that absolute encoder require no Sync as ACP keeps track of all correction throughout the sky and should remain static throughout time (barring frost upheavals, etc).

Where may lie the problem?

Cheers

I need a log file to see what's going on in detail. Please attach the log to a reply here. In general ACP's behavior (which hasn't changed in this regard for years) depends on whether your mount reports that it can be SYNCed or not. Assuming that yours can be synced, it will determine the coordinates where it is really pointed, sync the scope to those coordinates, then slew to the desired coordinates. Since the scope has been synced very close to the desired coordinates this should result in dead center pointing. If you are using the pointing corrector, though, this is different, and instead the syncs get turned into mapping points, etc. rather than write a book on all of this let me see a log and maybe I can be more specific.

Thank you a second time today, Bob.

I had conjectured the Sync was absorbed into the pointer corrector (sure wish I knew how, always interesting). I was looking into throwing 'cannot sync' back at ACP, and it makes sense for absolute encoders, as the bias can always be set once by the T/O for the life of the installation until a mechanical or electrical change is effected. Would this be a solution?

I have attached the zip of a not so marvelous night and also the log of my end of things.

Cheers

Let's turn off the pointing corrector first. Save the model though. Now run a night without it. That will tell us what you mount and flex use are doing. I don't see any 18 minute errors in your log. I see a 6 minute one then 2 minutes.

Note that ACP has a single sync option meant for encoder-equipped mounts. In this mode it will sync once to the mount then never sync (or add to the model) for the rest of the night. Possibly this is the right mode. We just need to know how the mount is doing.

Greetings Bob,

the last runs I sent you weren't the worst, but that wasn't the point, rather why is ACP slewing to the same offset coordinates that it synched to? I would have expected it to slew to the original image coordinates, which it does on the second slew after a sync, but not always. Attached another night's run.

An excerpt below from my end of logging;

22:55:21 Ascom: Telescope._SlewToTargetAsync Ra: 13:52:31 Dec: 23:43:29 The image target
22:55:21 Enc 109.561 HaBias -1.738 sid_deg 218.319 Ha 10.677 RA 207.642
22:55:34 Slewed to Ra: 13:52:46 Dec: 23:43:39
22:55:34 Enc 110.058 HaBias -1.738 sid_deg 218.372 Ha 10.180 RA 208.193
22:57:10 Ascom: Telescope._SyncToCoordinates Ra: 13:51:52 Dec: 23:43:27 We're off, let's Sync
22:57:10 Bias: update RA:-1.97 DEC:1.0
22:57:10 Enc 109.660 HaBias -1.967 sid_deg 218.775 Ha 10.807 RA 207.967
22:57:11 Ascom: Telescope._SlewToTargetAsync Ra: 13:51:52 Dec: 23:43:27 Why did we ask for the sync center?
22:57:11 Enc 109.660 HaBias -1.967 sid_deg 218.779 Ha 10.807 RA 207.972
22:57:18 Slewed to Ra: 13:52:02 Dec: 23:43:37
22:57:18 Enc 109.668 HaBias -1.967 sid_deg 218.808 Ha 10.799 RA 208.009
23:01:06 Ascom: Telescope._SlewToTargetAsync Ra: 13:52:08 Dec: 23:34:44 Ok, back to the desired approx image target
23:01:06 Enc 108.732 HaBias -1.967 sid_deg 219.762 Ha 11.736 RA 208.026
23:01:14 Slewed to Ra: 13:52:18 Dec: 23:34:43
23:01:14 Enc 108.754 HaBias -1.967 sid_deg 219.794 Ha 11.714 RA 208.081

I remember the re-slew to desired target at being spot on the same RA and Dec, but perhaps when the pointing correction was switched off it change this? Or is the small variation due to the residual on my end of things not re-slewing to the sync perfectly? This was an unattended run, so I was not around to more carefully see what was going on.

I have to admit I am tired this morning and have to do the 90 km drive into work, so I'm not up to figuring this stuff out, despite an espresso.


Cheers & much appreciated.

For a test, I changed my ASCOM Telescope CanSync property to false and re-enabled pointing corrections and ran ACP last night. The run look good, no issues to report and there are now 9 points in the table. I'll let it run for many more nights and report back if correction improve, which I am certain they will.

Cheers

Excellent Andre! Thanks for letting us know.