SSAG & PHD odd behavior?
Posted 02 October 2012 - 11:31 PM
Previous attempts at autoguiding used a webcam type setup with PHD and controlled my CG5GT via serial port. PHD would calibrate, lock on, and guide for a short amount of time (a few minutes), then would seem to get tired and no longer send appropriate compensation controls to the mount. Thus the star would start drifting.
That's exactly what I'm seeing using the ST4 port. I see PHD go through its cal routine, and it locks, and it guides for a little bit and then the star starts to drift.
Do I have to take out the backlash compensation? Is there anything else I need to do (other than polar align) to get this to work successfully? Thanks.
Posted 03 October 2012 - 03:19 AM
If all else fails, you can get a voltmeter and check to make sure your St-4 port is sending commands and then trace it back to the mount.
Posted 03 October 2012 - 03:51 PM
Posted 03 October 2012 - 11:34 PM
(1) polar alignment - I once thought I could just guide my way out of polar alignment, but the more you're off the bigger the correction signal PHD has to send and the greater the odds of a big swing in your guiding graph
(2) Try preventing PHD from switching the DEC guiding -- if it flips from north to south backlash'll kill you
(3) Make sure the max pulse guide PHD can send to the mount is enough to keep you on track, as Mike suggested above. I think I went up to 1200 ms
(4) If you haven't already, try taking your DEC axis apart, and replace the *BLEEP* sticky original grease with a good white lithium grease and maybe give the shaft a good buff with emery cloth if you feel any roughness anywhere. Instructions for this can be found on www.astronomyboy.com.
After doing the above I was getting reliable two-to-three minute subs, at 5-min subs I was about 60-70% success rate, and once in a while I could try to sneak in a few 8-min subs. Others more skilled in the art may be getting better performance :-)
Hope this helps
Posted 04 October 2012 - 12:40 PM
It seems unlikely to be an issue with the software.
Polar alignment - I have not done a precision polar alignment using the drift method. I do a rough polar align, then a 2-star align plus a calibration star.
Prior to getting the SSAG I could take 20 second exposures without too much error. I am hoping that even with a non-precision alignment I can get 60 seconds or more.
Hmm...I have now removed backlash compensation. I'll see what happens and report back. Is the N/S DEC thing a setting?
3) I will take a look at increasing the pulse width. I suspect this will likely fix much of my issue.
4) Oh boy, tell me about it! I have cleaned all that glue out and replaced it with white lithium grease. I did run some emery cloth over some rough spots but no where near a pro job.
I'm hoping for clear skies tonight to try out the suggestions!
Posted 04 October 2012 - 08:29 PM
And finally, the CG5 has a polar alignment routine in the handset. After your 2-star align plus a calibration star, try the polar alignment routine -- it's pretty slick, although it puts off your pointing alignment. For this reason many people recommend doing the alignment routine a second time after the polar align. I'm usually in too much of a hurry to do that and I just use the 'precise goto' function instead -- discovering that function made my life *so* much easier.