EQ6R-Pro RA guiding issues

[cfinn]

Hi all,

I'm having a few issues with guiding my EQ6R-Pro. Specifically, I am finding that guiding error in RA is 2-3 worse than in DEC and my overall guiding RMS is quite a bit larger than 1 arc-second. The results are varied through a guiding session, with stable periods and periods of large (2-3 arc-second peak-to-peak) oscillations in RA. I would expect to be regularly achieving < 1 arc-second guiding RMS with this mount based on other user reports and manufacturer's spec. It's worth noting however that this problem is virtually non-existent when I am guiding closer to the pole,  e.g. around Ursa Major, where I can achieve results as good as 0.5 arc second RMS quite easily and am consistently well below 1 arc-second. The problem emerges when I guide well away from the celestial pole. I talked through my issues with a few people on the StarGaZine Zoom call last night and am sharing here the full details and guide logs to source some more help in getting to the bottom of this problem.

A few details. On the mount I have an Esprit 120 and I am guiding with an Evoguide 50 and a ZWO ASI 120mm mini. I am attaching a photo of my setup and am fairly convinced I am following all the best practices with cable management, at least as far as is possible with this mount. Moving the scope into all feasible positions I experience no obvious cable snags. It's quite a heavy setup, getting on for 14kg I think, but this mount should be able to handle that. I have tried perfect balance (both axes) and balancing East heavy in RA and found very little difference in the results between them. In terms of guiding software, I am using KStars/Ekos and the built in guider. I have tried PhD2 as well and experience very similar results. I am using multi-star guiding with the Predictive PEC guiding algorithm with guiding exposure set to 1s, min-move set to 0.1 arc-seconds and aggressiveness parameters fairly middle of the road so I am correcting around half of the measured deviation. I am including a screenshot of my typical settings below. I have tried longer exposure times (up to 3s), and lower/higher aggressiveness parameters to no avail, so I am fairly convinced that my problems are not due to "chasing the seeing" or bad configuration, particularly since I see good results closer to the pole and bad results away from the pole on the same night with the same settings. In all configurations, if I am pointing more towards the celestial equator I see the same pattern of large RA oscillations that come and go in an apparently random way. You can see this in a screenshot I am providing from PhD2 log viewer. 

I am attaching two guide logs to help diagnose the problem. One is from a session on 23rd January, when I was imaging M81 and M82 (you can see the result here). Guiding on this session was good, and what I would expect from this mount. In this general area of the sky closer to the celestial pole, I am not experiencing any problems. The other log file is from last night, where I was imaging the Pleiades and it is quite erratic. This is quite typical when I am imaging closer to the celestial equator. You can ignore regular spikes in RA and Dec as this is where I was dithering.

Lastly, it was suggested to me on the Zoom call last night that I should take a look at the RA belt drive and see if there were any problems there. I am including a picture of this as well and there was nothing obviously wrong to me there. I don't feel any stiffness in the mount and everything moves quite freely. Certainly enough that I can deliberately balance and unbalance the mount at will.

I hope all of this detail will be useful in helping me to diagnose my issue and I would be extremely grateful for any help you can all give me.

Thank you,

Charles

guide_log-2021-01-23T20-31-58.txt guide_log-2021-02-28T19-05-28.txt

Edited March 1, 2021 by cfinn
Forgotten attachment

[david_taurus83]

That DSLR cable is giving me the heebie jeebies!

When the clutches are locked is there any play in the axis? Even the slightest when you try and pull on the counterweight bar? My AZEQ6 developed a bit of play after 6 or 7 months use. I had to dial it out using the Astrobaby guide and it was fine afterwards.

[cfinn]

10 minutes ago, david_taurus83 said:

That DSLR cable is giving me the heebie jeebies!

When the clutches are locked is there any play in the axis? Even the slightest when you try and pull on the counterweight bar? My AZEQ6 developed a bit of play after 6 or 7 months use. I had to dial it out using the Astrobaby guide and it was fine afterwards.

Thanks for your reply. And yes, that cable was a bit taught on this occasion. It could have had a bit more slack in it but pretty sure it's not an issue as it's plugged into the Pegasus PPBA on top of the scope.

I've had the mount since September and it had a bit of play in RA from new. Like you I dialled it out using the Astrobaby guide to the point where I can barely feel any backlash. Slewing the mount 360 degrees in both directions revealed no binding in the gears after that procedure so I stopped there. I could return to this and adjust some more but I am not sure there is much adjustment left in there before I get binding.

[cfinn]

I should also say, I have to use the counterweight extension to get balance in RA with two 5kg counterweights. I am aware that this is less than ideal and am thinking about getting an extra counterweight or two so I can balance with the weight further up the bar. Not sure if this is a possible cause or not.

[david_taurus83]

I know you say you've tried longer but 1 second exposures and a min move of 0.1 and the mount is going to try to react to every wobble of the guide star. Have you tried to run the guiding assistant in PHD?

[cfinn]

14 minutes ago, david_taurus83 said:

I know you say you've tried longer but 1 second exposures and a min move of 0.1 and the mount is going to try to react to every wobble of the guide star. Have you tried to run the guiding assistant in PHD?

Agree in general I should go for longer exposure and higher min move for exactly the reasons you suggest, though I do believe since I am using the new multi-star guiding I should theoretically be a little more robust to seeing. In any case, unfortunately this did not solve my problem and the same settings give me very good results nearer the pole.

I have run the guiding assistant in PhD. Attaching results here.

Edited March 1, 2021 by cfinn

[michael8554]

Hi Charles

Re your 28th Feb log:

For PHD2 it's recommended to Calibrate at Dec=0, your log shows Dec = 24.2 deg, maybe Ekos is different ?

Calibration guide speeds:  RA = 2.2 a-s/s, Dec = 1.9 a-s/s

Guide speeds are usually 8 a-s/s or more, perhaps Ekos is different ?

Despite the tiny guide speed, Calibration only took 6 steps. 12 is more normal for PHD2, but maybe that's normal for Ekos ?

PA is good, Dec requiring very few corrections, and correction of Dec Dithers is fast.

RA is choppy, which might be due to only 1 second exposures.

Correction of RA Dithers is within a couple of seconds.

Your Minimum Move is only 0.1 arcsecs, seems too low to me.

I'd look to the Guide Rates, Calibration, Min Move, and exposure, which might sort out the choppy RA.

Michael

 

 

[malc-c]

Thats a lot of gear on the mount.  Whilst it may be balanced, the CoG may be out.  There are some old but good videos on youtube from Astronomy Shed that show how to arrange the mass in a way that perfectly balances the set up

 

[cfinn]

36 minutes ago, malc-c said:

Thats a lot of gear on the mount.  Whilst it may be balanced, the CoG may be out.  There are some old but good videos on youtube from Astronomy Shed that show how to arrange the mass in a way that perfectly balances the set up

 

Yes, interesting. I had the problem described in this video where I could not achieve balance along a third axis and interestingly I found that adding the finder (which I don't use for imaging) fixed it. This confuses the hell out of me, because without it there doesn't look like there is anything off-centre that could cause an issue. I will probably revisit this and think about it some more.

[cfinn]

2 hours ago, michael8554 said:

Hi Charles

Re your 28th Feb log:

For PHD2 it's recommended to Calibrate at Dec=0, your log shows Dec = 24.2 deg, maybe Ekos is different ?

Calibration guide speeds:  RA = 2.2 a-s/s, Dec = 1.9 a-s/s

Guide speeds are usually 8 a-s/s or more, perhaps Ekos is different ?

Despite the tiny guide speed, Calibration only took 6 steps. 12 is more normal for PHD2, but maybe that's normal for Ekos ?

PA is good, Dec requiring very few corrections, and correction of Dec Dithers is fast.

RA is choppy, which might be due to only 1 second exposures.

Correction of RA Dithers is within a couple of seconds.

Your Minimum Move is only 0.1 arcsecs, seems too low to me.

I'd look to the Guide Rates, Calibration, Min Move, and exposure, which might sort out the choppy RA.

Michael

 

 

Thanks Michael. It might well be worth it to me to revisit some of these things. The calibration in particular I have not paid much attention to and I just let Ekos do its thing, but I will have a play and/or switch to PHD. I was vaguely aware that calibrating near/on the celestial equator was a good thing to do and that you should re-use this calibration elsewhere. By default Ekos will re-calibrate every time you switch to a new area of sky, but I do believe there is an option to override that.

[michael8554]

If Cal on Target is the norm for Ekos then stick with that.

A good Calibration is crucial for good guiding.

Michael

[cfinn]

Another guide log from last night. Min move increased to 0.4". Guiding exposures of 2 or 3 seconds just made things worse, so I had to stick with 1 second. Made great efforts to balance the mount properly on all 3 axes, before making RA a little east heavy. It's a real struggle to get guiding RMS < 1". At one point RA axis goes crazy and oscillates +/- 10"! Re-calibrated a couple of times and tried upping the number of iterations in Ekos. Dec looks strange to me - could be backlash? Opinions again would be very welcome. Performance is some way below what I was expecting from this mount, which is disappointing.

guide_log-2021-03-07T19-27-58.txt

[7170]

I would work on getting your PA better than 2.1 arc min. Then use use multi-star guiding (in the latest version of EKos) with an exposure of 3-5 seconds, and try 2x2 binning.

If the above doesn't improve things then go into indi control panel and EQMod tab and try a custom RA guide rate (slight lower than the default) and see what happens. Is RA still choppy or gradually getting worse over time without choppyness if you disable RA guiding. You maybe able to use a custom speed with RA guiding in one direction only for RA. 

Also try east or west heavy balance depending on the location in the sky you image.

If it were me I would definitely try is slowing down RA guiding using a custom speed and then guide in one direction only. If it still has issues I would suggest the mount hardware needs a tune up. 

Also looks like the photo is near the house, if you are pointing anywhere in that direction thermals from the roof etc are probably going to impact the guide star a lot.

[7170]

4 hours ago, cfinn said:

At one point RA axis goes crazy and oscillates +/- 10"!

Looks like you had dither on from the log? For testing I would turn it off.

[michael8554]

If Ekos is based on PHD2, then PA of 5arcmins or better should be easily guided out, and in fact Dec guiding is fine.

From the Log:

First two Cals were rubbish, with wildly different RA and Dec guide rates reported.

The final one Calibrated RA and Dec in 8 steps, but Dec took 24 steps to return !

Those 16 extra steps are Dec Backlash or Stiction.

As mentioned before, reported Guidespeeds seem very low  - Calibration guide speeds: RA = 1.6 a-s/s, Dec = 2.2 a-s/s

PHD2 expects 8 a-s/s or more, so is this normal for Ekos or not ?

Dec PA and guiding on the last long run is good, 0.49 arcsecs guide error.

RA was 0.89 with 2 sec exposure, and 0.81 with 1 second exposure, not hugely worse.

A sensible guide rate at 2 seconds might give the guiding a chance.

I saw the short spell of +/- 10arcsec oscillation, can't see any reason for that I'm afraid.

Analysis of these PHD2 "Clones" is difficult because so many important PHD2 features have been stripped out.

Michael

 

Edited March 8, 2021 by michael8554

[cfinn]

28 minutes ago, michael8554 said:

If Ekos is based on PHD2, then PA of 5arcmins or better should be easily guided out, and in fact Dec guiding is fine.

From the Log:

First two Cals were rubbish, with wildly different RA and Dec guide rates reported.

The final one Calibrated RA and Dec in 8 steps, but Dec took 24 steps to return !

Those 16 extra steps are Dec Backlash or Stiction.

As mentioned before, reported Guidespeeds seem very low  - Calibration guide speeds: RA = 1.6 a-s/s, Dec = 2.2 a-s/s

PHD2 expects 8 a-s/s or more, so is this normal for Ekos or not ?

Dec PA and guiding on the last long run is good, 0.49 arcsecs guide error.

RA was 0.89 with 2 sec exposure, and 0.81 with 1 second exposure, not hugely worse.

A sensible guide rate at 2 seconds might give the guiding a chance.

I saw the short spell of +/- 10arcsec oscillation, can't see any reason for that I'm afraid.

Analysis of these PHD2 "Clones" is difficult because so many important PHD2 features have been stripped out.

Michael

 

Thanks Michael, I appreciate you taking a look at these for me. To be honest, I don’t know how to change the calibration guide speed in Ekos, or what is normal here. There is a setting for the number of iterations and the pulse length, so maybe it’s the latter? Next time I think I’ll use PHD2 and do a proper run of testing. I was trying to image here, rather than specifically testing the guiding parameters. Sounds like I need to take a look at Declination backlash and stiction so I will do that.

Charles

[cfinn]

2 hours ago, 7170 said:

I would work on getting your PA better than 2.1 arc min. Then use use multi-star guiding (in the latest version of EKos) with an exposure of 3-5 seconds, and try 2x2 binning.

If the above doesn't improve things then go into indi control panel and EQMod tab and try a custom RA guide rate (slight lower than the default) and see what happens. Is RA still choppy or gradually getting worse over time without choppyness if you disable RA guiding. You maybe able to use a custom speed with RA guiding in one direction only for RA. 

Also try east or west heavy balance depending on the location in the sky you image.

If it were me I would definitely try is slowing down RA guiding using a custom speed and then guide in one direction only. If it still has issues I would suggest the mount hardware needs a tune up. 

Also looks like the photo is near the house, if you are pointing anywhere in that direction thermals from the roof etc are probably going to impact the guide star a lot.

Many thanks.

I’m using a QHY Polemaster for polar alignment and am reasonably satisfied I’m getting it as accurate as I can manage. As Michael mentioned, I’m not seeing many dec corrections, so assuming my PA is good enough. I’m also using multi star guiding already and 2x2 binning on the guide cam is not sensible for me as I’m using a 240mm FL guidescope.

I think your comments around guide speed and direction are interesting. I’ll give that a go.

Charles

[Schneebauelli]

If you could not fix the problem. Have a look at your belt and compare the tightness of the RA - Belt with the tightness of the DEC-Belt. They should be around the same and the belt should be stretcheable with a light touch by 1-2 mm. As from your guidelogs it is clearly visible that you have some high frequency patterns with a period of 13.6s in the first two logs and in the newer log it has a 21 second period which can not be guided out easily or be removed with PPEC. In all three logs those high frequency disturbances have magnitudes of at least 0.5 " and contribute to a lot of your total RA error. I would expect that the RA belt is a bit loose or does not fit perfectly. Try to adust it, do not overthighten it, and have again a look at the frequency analysis of the PHD-Log viewer and see if something changed for the better. I had a similar problem when i got my new EQ 6-R Pro and got rid of the highfrequency disturbances by slightly tightening the RA belt to the same level as the DEC -Belt.

When adusting loosen the 3 screws a bit that hold the RA motor in place then tighten the little Allen Screw between the two gears a little bit to increase the tightness of the belt. Before putting everything back together plug it in and check if everything works/sounds smoothly as before.

Cheers Schneebäuelli