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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

--
Paul Goelz
Rochester Hills, MI? USA
pgoelz@...