On 12/11/2020 11:46 PM, Brian Valente wrote:
RA seems to me to show issues related to a bad PEC. you have a lot of back-and-forth
looking at your raw RA, i can't even make sense of the calculated raw periodic error with is another sign of bad PEC
image.png
Your included image looks perfectly understandable to me. It shows RA errors at three important frequencies.... worm, worm X2 and worm bearing. It also matches the frequency domain plot I get in PECPrep.
See my comments below.
my suggestion is next run please do a guidelog that includes a calibration run, and do not use PEC at all.
Please note that only a small part of that 100 minute run was with PEC on. For the bulk, PEC was off because I have always found PEC makes things marginally worse. The run began with PEC off. Somewhere near the middle of that run I trained the PEC, which leaves PEC on after the training ends. Including the training, it was on for a total of maybe 5-10 minutes at most and when it looked on the guiding graph like RA was the same or worse, I turned it off again. If you look at the entire run in the time domain, you will note that the RA looks different for a stretch in the middle of that run.
I had a look myself at that log in PECPrep and I see significant peaks in the frequency domain at the worm fundamental and second harmonic. The highest peak by far, though, is at 76.2 which corresponds to "worm bearing (ball passes outer race)". The bearing signal at 76.2 is double the worm fundamental signal signal at 239.4 and triple the worm 2nd harmonic signal at 118.7. See attached screen grab.
The worm fundamental (239.4) I understand. The second harmonic (118.7) would seem to indicate an possible alignment issue with the Oldham coupler? The worm bearing signal at 76.2 could indicate the worm block might be crooked and in need of alignment?
Note that for now, the RA axis on this mount is 100% as-received. I have not touched it but I am willing to do the same adjustments that helped the DEC axis if needed. When I was working through the DEC backlash issue I checked the RA on a terrestrial target and found the backlash was around 2000mS. Since backlash is not an issue in RA I just left it alone. But it would be easy to loosen the outer worm block cover screw and make sure the block was well aligned if that might be responsible for the large signal at 75s.
Today I am going to have a look at all the old PHD2 logs that are stored from past sessions and see if there is anything consistent in them.
when you calibrate, make sure it's near the intersection of the meridian and celestial equator
Yes, that is always how I calibrate.
I rotated the guide camera yesterday to match the orientation of the main camera so the next time out I will re-do the calibration. And unless it is a really good night I'll also get about 30 minutes unguided to see what that looks like.
I also discovered that the RA axis was not perfectly balanced. It was VERY close (only noticeable by how long the axis coasted after being pushed) but not perfect. The slight unbalance biased the axis to the east on the east side of the pier and to the west on the west side. slightly. I have since corrected that imbalance.
Paul
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Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com
