Problems with Mount / Guiding

[Liudas B]

Hello everyone!

I am having problems with guiding my EQ6i PRO (renewed NEQ6?) mount.

Sharing the details and details:

• SVBONY SV106 50mm guide scope + ASI 120MM-S / Askar 65PHQ (native FL). Guiding system is on top of the APO, not in the finder bracket.

• Polar Alignment: for the time being, I am trying out everything in my balcony (can't see Polaris), so I polar align with NINA's TPPA - getting good (to my knowledge) results to 1-2arcmin's (even lower sometimes).

• RA axis is made a bit "east heavy" - barely affected more by gravity.

• DEC axis is made a bit "camera side heavy" - barely affected more by gravity.

• Using NINA for acquisition/control - PHD2 for guiding - GSS as mount control system (no backlash settings set). Everything is controlled using SV241 and miniPC.

I set up everything and out of the box, with first calibration PHD2 showed me about +6000ms DEC backlash. Mount tracking itself and even with guiding - it was pretty bad. Further more, it is my first solid GEQ mount so I didn't know what its normal operating sound should be - when slewing each axis, it had weird sound, like grinding/skipping or something like that. Wrote to the retailer and after dropping out the side factors, we came to conclusion that worm gears needs to be tunned up. And yesterday I carefully followed the AstroBaby's and Cuiv's (YT) worm gear tuning guide - and holy moly, the grinding sounds dissapeared! Did the tune up till it was close to binding, but not there yet - sounds are very smooth now, compared to out of the box situation.

But the DEC backlash is still there, PHD2 showing about 5800ms! And one more thing I noticed after the worm tuning, is that the counterweight is now a bit loose (click-clacking?). After all tunes it still shows problem with DEC axis slewing to South - it has a major delay.

And now a further problem is visible from the guiding logs - after specific time periods, DEC axis shoots up north side to 10RMS or so and doesn't go back to south side!


What am I not seeing or understanding - does it need further tune, how should I do it then? What to notice? I am a bit lost in this and require some guidance (not only my mount xd), thank you all in advance - let me know if you need any further information!

• Before RA+DEC Tune:

• After RA+DEC Tune:

• After the initial tune (by the sound it looked good) - so 2nd tune GA backlash graph still shows major problems with south slewing:

Attaching the guidelog from yesterday  .GuideLog_ 03.27

[Bruce Waddington]

You probably have a number of problems that you will need to work through one at a time.  It looks like your finder-scope guiding arrangement may be flopping around on its own as seen in this example:

The arrows point to places where you got an abrupt 10 arc-sec movement in both RA and Dec.  This occurred during the Guiding Assistant session so there was no guiding being done and the Dec axis motor wasn't even running.  Until you eliminate these kinds of problems, guiding is going to be all over the map.  The GA run also suggested that you try to improve the focus on the guide camera - have you done that?  Your log also shows repeated calibration attempts even though you got a 'good' calibration at 00:02.  Once you get a good result like that, keep using it, don't over-write it with a later calibration that is likely to have lower quality.  You mentioned in your narrative that you intentionally put the Dec axis slightly out of balance - why?  That doesn't accomplish anything, you need to keep the Dec axis in balance.  

Once you get this basic stuff sorted out, you can move on to dealing with whatever mechanical shortcomings you have in the mount, including Dec backlash or stiction.  A good way to make those measurements is to follow the procedure in the attached document.  To be completely thorough, you should extend the instructions to include a 15-20 minute guiding session on both sides of the pier.  By the way, working from a balcony is likely to introduce a bunch of problems that will be difficult to identify.  This is especially true if you are also working in an area with a lot of heat convection.  For that matter, some of these large guide star excursions we see in the log might be caused by having the gear bouncing around on a balcony.  Guiding is a precise business, best done on the ground with a solid base.

Bruce

[Liudas B]

Hello!

First of all, thank you Bruce, for all the tips and investigations in this matter, really appreciate it!

" It looks like your finder-scope guiding arrangement may be flopping around on its own as seen in this example" - I checked out all the connections and bolts, there is absolutely nothing loose. Maybe I could've made a vibration etc. near the mount to what have caused it?

" The GA run also suggested that you try to improve the focus on the guide camera - have you done that?" - I have a problem with that, as I try to focus it, it doesn't get better with the Star Profile. The lowest I can get is approximately HFD of 5, give or take. Maybe there are some important settings regarding that? Maybe I wacked off something!

" Your log also shows repeated calibration attempts even though you got a 'good' calibration at 00:02." As I understood, when you change anything with the mount, I should re-do the calibration? Or you should do it only per "PHD2 Best Practices" guide?

"You mentioned in your narrative that you intentionally put the Dec axis slightly out of balance - why?" - I thought that it is always better to do the axis slightly out of balance, because in perfect balance your mounted weight kind of "floats" within the gears. Am I wrong here? Should it be at perfect balance every time?

And yes, I understand that I will have difficulties in the balcony in any scenario, you are absolutely right here! For the time being, wanted to check how everything works and what problems I could face in the field - of course there will be a lot less of the problems, as you have mentioned the factors.

Now regarding further troubleshooting, I had some clear skies on saturday evening. Followed all your tips about balance, still couldn't get my star to lower than HFD of 5 (maybe I am missing something here?), and with the current DEC backlash of about 5000 - 6000ms - managed to get the guiding to about 1RMS and I could say that it was pretty stable. I will share the guide log in the evening, sadly forgot to upload it from PHD2!

Once again, I am very thankful for all the support you are giving me! I am truly learning a lot with problems like these and other caveats. With next clear skies I will try to do everything step by step with your shared PDF guide and other tips provided.

[Brian Valente]

Liudas

>>> With next clear skies I will try to do everything step by step with your shared PDF guide and other tips provided.

I suggest you focus on completing the baseline guidelog from the PDF and share it here. It will tell us a lot about the performance of your system, including without any guiding.

That is a good next step for you

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Liudas B]

Will do that Brian, thank you very much and appreciate it!