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Guiding Drift, Balance and RMS - EQ6-R Pro

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#1 blueplanetphoto

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Posted 12 May 2021 - 01:36 PM

I've been at this for only a bit over a couple months now. But, I started out with a total RMS of 0.11, then began averaging 0.25, and now it's between 0.35 - 0.45, often beginning the session at around 0.25 but gets worse over the course of the session. You can see in the attached images, the total RMS at the beginning of the session was 0.27 and toward the end in the second image is 0.46 and the graph is more jagged. I'm certainly losing guiding precision as the night wears on. This seems to be the typical pattern of late; a more open graph at the start and a more closed, jagged graph near the end. I've wondered about stiction because the RA and DEC axes are fairly tight - it takes a significant counterweight movement to create an out-of-balance situation and there's a relatively wide range of counterweight placement where the balance seems fine (the zone is about 2-3 inches on the counterweight shaft). I have what looks to be a lot of wide RA and DEC movement on the PHD2 graph, but the RMS seems stable enough (typically between 0.25 - 0.35 total RMS). I polar align now using a Polemaster, but prior to that, total RMS was between 0.11 - 0.15. In the last couple weeks of imaging the same target (M101).  APT puts M101 directly on target, but  over the session, drifts "upward" and to the "left", which would be, I think, Southeast (working upside-down and reverse, attached photos), then seems to move straight up, or South. For me at 45 deg N, M101 is pretty much at the zenith, so the scope is pointed nearly straight up.

 

My mount is EQ6-R Pro and I'm using one counterweight with an Explore Scientific ED102 FCD100. The counterweight is positioned at around the middle of the counterweight shaft with the extension added - where the two fit together. Over this past couple months I've spent some time ensuring my cables are secure and don't pull or pinch or wrap around any knobs other bits. The tripod is dead level on footings/pavers I added to the backyard. I've examined my process now versus how I was setting up at the beginning and the things that have changed are: tightening down and securing cables and accessories (Pegasus Powerbox Advance) and adding the Polemaster for polar alignment. I've also completed one session of PEC training, but it doesn't seem to matter whether I have PEC enabled or not in the total RMS and RA/DEC corrections. I'm getting pretty decent polar alignment with the Polemaster versus what I think I was getting using the polar scope and PS Align iPhone app. But maybe that's not true. I've attached  a couple screenshots of the drift. The first image is about 25% through the session (after being dead center) and the second image is near the end of the session with M101 out of the central box by a noticeable distance. 

 

My PHD2 guiding graph looks like a mountain range reflected in a still pond even though the RMS seems reasonable, from what I know.

 

Any suggestions would be helpful. What can cause this drift? Is it balance? Stiction? I've read where others with the EQ6-R Pro have a more freely-moving RA and DEC axes whereas mine seem fairly "stiff". A combination? 

 

Thank you.

Attached Thumbnails

  • drift-11-1000.jpg
  • Drift-21-1000.jpg


#2 Between17

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Posted 12 May 2021 - 06:01 PM

Hi Mike,

 

I have an EQ6R Pro also, but have never used APT. I can make a couple comments that I hope are helpful for you to narrow things down.

 

It is odd that the target is drifting. One possibility might be that PHD2 has lost the guide star briefly at some point in your session, stopped guiding so the target drifted, then reacquired a guide star and continued on. You should be able to see this if you blink through your subs, or by reviewing your PHD2 guide log using the PHD2 Log View tool.

 

Also related to the drifting, how do the stars look? For 180s subs if there is continuous drift your stars may well be oblong shaped.

 

As for balance, I have a 4" refractor with a few accessories, it weighs around 25lbs. I need two weights for it on the EQ6R Pro, one is fully down the shaft the other about 3/4 of the way down. It sounds like you are using less weight. My mount also moves freely in both axis though. If you think you are having stiction in your mount you can reference the PHD2 documentation, there is an example in there of what stiction looks like to PHD2.

 

I have fooled around with PEC/PPEC also, but not consistently gained anything from it yet. I believe the best practices in PHD are to just leave PHD2 in the default guiding algorithms unless you really know what you are doing. Your DEC and RMS error seem pretty similar so I am not sure you would gain much by improving the RA guiding without improving the DEC error as well.

 

Another thing is are you getting a good calibration in PHD2 at the start of each session, and then running the Guiding Assistant to get your base parameters set including the DEC backlash comp?

 

I think in guiding that the error is normally referenced in arc sec, so your errors above would be 1.8" and 3.04", not 0.27 & 0.46 pixels. This makes it more meaningful to compare errors across different systems. Others may correct me on this. FWIW I have a 4" 106mm FL scope on my mount and normally get well under 1" RMS. But some nights not!



#3 Woodbridge_Dave

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Posted 12 May 2021 - 09:00 PM

Let’s start with basics.  In that graph your RMS is not 0.46, it’s 3.04.  It is likely you’ve been getting high RMS values all this time and what you thought was 0.11 was something else.   


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#4 michael8554

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Posted 13 May 2021 - 08:44 AM

As Dave said, you've been quoting pixel error, not arcsec error. But nevertheless we get the drift.

 

Have you been Calibrating at Dec = 0 ?

 

You seem to be driving RA and Dec hard, which is giving those sawtooth responses.

 

Have you run the PHD2 Guide Assistant, to get suitable Minimum Move settings for the session ?

 

Including Dec Backlash Compensation ?

 

With perfect PA, Dec shouldn't need guiding at all, that again points to MinMo being set too low, giving unnecessary corrections.


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#5 blueplanetphoto

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Posted 13 May 2021 - 11:26 AM

Let’s start with basics.  In that graph your RMS is not 0.46, it’s 3.04.  It is likely you’ve been getting high RMS values all this time and what you thought was 0.11 was something else.   

 

Thanks, Dave. I have misread the information in my self-teaching. That info helps. 


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#6 blueplanetphoto

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Posted 13 May 2021 - 12:46 PM

As Dave said, you've been quoting pixel error, not arcsec error. But nevertheless we get the drift.

 

Have you been Calibrating at Dec = 0 ?

 

You seem to be driving RA and Dec hard, which is giving those sawtooth responses.

 

Have you run the PHD2 Guide Assistant, to get suitable Minimum Move settings for the session ?

 

Including Dec Backlash Compensation ?

 

With perfect PA, Dec shouldn't need guiding at all, that again points to MinMo being set too low, giving unnecessary corrections.

Thanks, Michael. Yes, I've run the guide assistant several times and applied recommendations. For my location, that's usually been in the vicinity of Arcturus, not quite on the equator, but within +/-20 deg. I'll try to get closer next time.



#7 blueplanetphoto

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Posted 13 May 2021 - 01:32 PM

Hi Mike,

 

I have an EQ6R Pro also, but have never used APT. I can make a couple comments that I hope are helpful for you to narrow things down.

 

It is odd that the target is drifting. One possibility might be that PHD2 has lost the guide star briefly at some point in your session, stopped guiding so the target drifted, then reacquired a guide star and continued on. You should be able to see this if you blink through your subs, or by reviewing your PHD2 guide log using the PHD2 Log View tool.

 

Also related to the drifting, how do the stars look? For 180s subs if there is continuous drift your stars may well be oblong shaped.

 

As for balance, I have a 4" refractor with a few accessories, it weighs around 25lbs. I need two weights for it on the EQ6R Pro, one is fully down the shaft the other about 3/4 of the way down. It sounds like you are using less weight. My mount also moves freely in both axis though. If you think you are having stiction in your mount you can reference the PHD2 documentation, there is an example in there of what stiction looks like to PHD2.

 

I have fooled around with PEC/PPEC also, but not consistently gained anything from it yet. I believe the best practices in PHD are to just leave PHD2 in the default guiding algorithms unless you really know what you are doing. Your DEC and RMS error seem pretty similar so I am not sure you would gain much by improving the RA guiding without improving the DEC error as well.

 

Another thing is are you getting a good calibration in PHD2 at the start of each session, and then running the Guiding Assistant to get your base parameters set including the DEC backlash comp?

 

I think in guiding that the error is normally referenced in arc sec, so your errors above would be 1.8" and 3.04", not 0.27 & 0.46 pixels. This makes it more meaningful to compare errors across different systems. Others may correct me on this. FWIW I have a 4" 106mm FL scope on my mount and normally get well under 1" RMS. But some nights not!

Thanks, I'll look into that. It's odd with the drift that the stars are not distorted like one might expect (oblong), though there is a slight point at one direction which could be classified as "egg shaped" which, on another forum, I read might indicate the guide star is too far away from the target (and too far north or south of the target). I'll pay more attention to that tonight when I run some more guiding tests. I also need to check and adjust my guide scope/telescope alignment, though with the Polemaster it's not supposed to matter. I would like to make sure they are parallel. I've run the PHD2 guide assistant several times and applied recommendations. Tonight looks to be another practice/training night. I'll set up guiding from the beginning, checking guide scope orientation later today, start off the night with a new calibration, new guide assistant session. I'll try guiding with the Polemaster polar alignment, Sharpcap polar alignment, and manual alignment, and see if there is a significant difference. I'll look back at my earlier guide logs to check the error, if it was just as bad then as it is now. 

 

As for balance, my scope and accessories weighs in at 14.5 lbs, perhaps 2/3 lb of cables. I could try the second counterweight. Maybe the mount is not weighted enough. Worth a try before I get into the guiding sessions and I can do that this afternoon while I'm checking the guide scope alignment. 

 

I'm self-teaching, like many have, so any help, suggestions, clarifications, is welcome. I taught myself photography and it took a while to become competent, so I'm not expecting an APOD tomorrow.  



#8 Between17

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Posted 13 May 2021 - 05:49 PM

 "egg shaped" which, on another forum, I read might indicate the guide star is too far away from the target (and too far north or south of the target).

This could well be true, but I have not heard of it before.

 

I don't think you need to get too precise about the alignment of the guide scope and your main scope. As you mentioned I don't believe it matters. But that being said I have mine somewhat aligned!

 

I'm  at a similar latitude to you, I also have a good view of Arcturus from my yard but have found that getting below Arcturus and closer to the horizon helps with PHD2 calibration.

 

Post your PHD2 guide log, that would be helpful to figure out more.

 

Good luck!

Dan



#9 MikeECha

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Posted 14 May 2021 - 06:26 AM

 

 

"Any suggestions would be helpful. What can cause this drift? Is it balance? Stiction? I've read where others with the EQ6-R Pro have a more freely-moving RA and DEC axes whereas mine seem fairly "stiff". A combination.."

You should fix the mechanical problems first. No amount PHD, PEC or whatever mix of electronics and software can fix that.

 

If you feel stiffness on your axis without load on them, you need to start there. One because shafts exist to rotate freely and also because you do not know if you are actually balanced. Friction may keep the axis balanced in one position and then give out and leave the axis unbalanced just few degrees of rotation down. That will produce a PHD2 graph like the one you see.

 

To give you some reference: My mount out of the box, with the CW bar horizontally if I released the clutch and let go of the bar, the head would not rotate more than 10-15 degrees before a full stop. There is no way that a motor can tract at sub arc-sec precision that way. 

 

So my point/advise to you is get the friction out of your axes first, then balance and see how the PD2 graph looks now. I bet you will see your RMS to come down to about .9-.8 arcsec (not pixels) or better.

 

I hope this helps



#10 michael8554

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Posted 14 May 2021 - 10:18 AM

"Yes, I've run the guide assistant several times and applied recommendations. For my location, that's usually been in the vicinity of Arcturus, not quite on the equator"

 

GA is best run "On Target", not at Dec = 0.



#11 blueplanetphoto

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Posted 14 May 2021 - 01:21 PM

"Yes, I've run the guide assistant several times and applied recommendations. For my location, that's usually been in the vicinity of Arcturus, not quite on the equator"

 

GA is best run "On Target", not at Dec = 0.

Sorry, not clear in my response to two different questions. Guide assistant is run on target, calibration is near Dec=0, two separate operations. Next clear night I will calibrate closer to the equator. 



#12 blueplanetphoto

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Posted 14 May 2021 - 04:52 PM

You should fix the mechanical problems first. No amount PHD, PEC or whatever mix of electronics and software can fix that.

 

If you feel stiffness on your axis without load on them, you need to start there. One because shafts exist to rotate freely and also because you do not know if you are actually balanced. Friction may keep the axis balanced in one position and then give out and leave the axis unbalanced just few degrees of rotation down. That will produce a PHD2 graph like the one you see.

 

To give you some reference: My mount out of the box, with the CW bar horizontally if I released the clutch and let go of the bar, the head would not rotate more than 10-15 degrees before a full stop. There is no way that a motor can tract at sub arc-sec precision that way. 

 

So my point/advise to you is get the friction out of your axes first, then balance and see how the PD2 graph looks now. I bet you will see your RMS to come down to about .9-.8 arcsec (not pixels) or better.

 

I hope this helps

Thanks, I've thought from when I first received it that movements in the axes were stiffer than they should be, but I don't have another mount or experience to compare to, so I'm making some assumptions based on what I've read from others regarding the ease of movement of the two axes. I've manually tested RA and DEC movements without scope and counterweights, with axes unlocked and it seems that DEC is more difficult to move than RA. I have to exert more pressure on Dec to get it to rotate. I notice on the Dec axis it does stick slightly then release as I rotate it. The RA axis has a scraping/rubbing sound when the counterweight shaft is moved side-to-side when upward vertical, but not downward vertical or horizontal. I've made videos of the Dec movement and the sound of the RA scraping. I've uploaded them here:

 

Dec axis movement

https://youtu.be/d6pY8j8gdyY 

 

RA movement and rubbing noise (noise not heard during regular slewing)

https://youtu.be/H2uZPhwxnEA



#13 MikeECha

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Posted 14 May 2021 - 05:24 PM

Thanks, I've thought from when I first received it that movements in the axes were stiffer than they should be, but I don't have another mount or experience to compare to, so I'm making some assumptions based on what I've read from others regarding the ease of movement of the two axes. I've manually tested RA and DEC movements without scope and counterweights, with axes unlocked and it seems that DEC is more difficult to move than RA. I have to exert more pressure on Dec to get it to rotate. I notice on the Dec axis it does stick slightly then release as I rotate it. The RA axis has a scraping/rubbing sound when the counterweight shaft is moved side-to-side when upward vertical, but not downward vertical or horizontal. I've made videos of the Dec movement and the sound of the RA scraping. I've uploaded them here:

 

Dec axis movement

https://youtu.be/d6pY8j8gdyY 

 

RA movement and rubbing noise (noise not heard during regular slewing)

https://youtu.be/H2uZPhwxnEA

Yes I see the DEC is stock. When you spin it, it should turn freely 2-3 times. The noise from the RA I think is coming from the green scale. If you loosen the scale thumb screws does the noise go away?

 

From normal life experience you probably know that shafts and bearings exist to rotate without/minimal friction. Motors of all kinds should come to mind. You do not need any expert to confirm it. It is like the sun rises on the east every day. 

 

The fix for the DEC takes about two minutes. Here what I wrote in another post

 

"...The friction while balancing comes from the taper bearing retaining nuts that come way overtightened from the factory. It happened to me and many other in the forum. It is just a "genetic disease" that SW claim to be normal...The fix for DEC is very simple. You see that round piece where the CW shaft comes out of? That is also the retaining nut for the DEC bearing.

To do this for the DEC axis, first check how tight the DEC axis is. Remove everything from the scope including the CW. Release the DEC clutch and spin the saddle. If there is friction the saddle will no spin very much (as mine was). Now, loosen the three set screws inside the little holes around that round piece by the CW shaft and just loosen thee round piece by hand just a bit at a time while rotating the saddle side to side with the other hand. The repeat the spin. Do this until you find the maximum amount of tightening that still allows the saddle to spin freely a for a couple of turns. It will not turn as freely as normal motor shaft because the saddle is center off balanced.

 

That is it for DEC. RA is slightly more complicated but still doable once you know what to do and have the right tool you will need. The nut for the RA is behind the polar scope and you will have to remove it to do the job. "

 

You need a spanner wrench for the RA. But very easy too.



#14 blueplanetphoto

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Posted 14 May 2021 - 06:37 PM

Thank you, MikeEcha,

 

I'll look at that. The Dec definitely doesn't rotate freely.



#15 blueplanetphoto

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Posted 14 May 2021 - 06:52 PM

One other thing I just remembered. When pointing at the zenith, then slewing back to the home position, the scope starts its way back, moves about 3 inches then stops. After a couple seconds it continues to the home position. There was one time that it just stopped after the 3-inch move and I manually put it back into home position to break down for the night. I don't know if this is related to the other issue, but just remembered it.



#16 Between17

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Posted 14 May 2021 - 09:44 PM

I second MikeEcha's suggestion to work on the mechanical issues first. Also agree with his assertion that PHD2 will not fix those kinds of problems, but suggest that it can be helpful in their diagnosis.

 

My EQ6R-Pro also some kind of strange pause like yours in certain situations. I have noticed it mostly on meridian flips where it will start to move, pause just long enough to alarm me, then continue. But it has never actually failed to continue moving after the pause.



#17 tboss70

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Posted 14 May 2021 - 10:22 PM

I just watched your videos and checked my EQ6R Pro Dec and RA and mine appear to be similar to yours. The dec almost identical. The RA seems to move a little more freely than the DEC. That said, I've used mine with PHD2, no PEC, a 4 inch refractor and a 60mm guide scope and here were my results.

 

Attached Thumbnails

  • rms 1.PNG


#18 blueplanetphoto

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Posted 01 June 2021 - 09:41 AM

Yes I see the DEC is stock. When you spin it, it should turn freely 2-3 times. The noise from the RA I think is coming from the green scale. If you loosen the scale thumb screws does the noise go away?

 

From normal life experience you probably know that shafts and bearings exist to rotate without/minimal friction. Motors of all kinds should come to mind. You do not need any expert to confirm it. It is like the sun rises on the east every day. 

 

The fix for the DEC takes about two minutes. Here what I wrote in another post

 

"...The friction while balancing comes from the taper bearing retaining nuts that come way overtightened from the factory. It happened to me and many other in the forum. It is just a "genetic disease" that SW claim to be normal...The fix for DEC is very simple. You see that round piece where the CW shaft comes out of? That is also the retaining nut for the DEC bearing.

To do this for the DEC axis, first check how tight the DEC axis is. Remove everything from the scope including the CW. Release the DEC clutch and spin the saddle. If there is friction the saddle will no spin very much (as mine was). Now, loosen the three set screws inside the little holes around that round piece by the CW shaft and just loosen thee round piece by hand just a bit at a time while rotating the saddle side to side with the other hand. The repeat the spin. Do this until you find the maximum amount of tightening that still allows the saddle to spin freely a for a couple of turns. It will not turn as freely as normal motor shaft because the saddle is center off balanced.

 

That is it for DEC. RA is slightly more complicated but still doable once you know what to do and have the right tool you will need. The nut for the RA is behind the polar scope and you will have to remove it to do the job. "

 

You need a spanner wrench for the RA. But very easy too.

Finally had clear skies to test this out. I made the adjustment to DEC (still just guessing at the tightness or looseness) and guiding has improved to 1.2-ish. RA is still a bit wonky, so I will look at that next. Last night I added the second counterweight, also. I don't know if that helped, so I will try again tonight with just one and see if the results are different. I also went through my cables from scratch and rearranged them and took care of some possible cable movement, and made a makeshift bracket for my Powerbox Advance to keep it from shifting on the OTA. 

 

One thing I've also had an intermittent problem with is (which I'll put in another post, specifically) is PulseGuide command failure. In PHD2, I will get this error now and then. I notice that DEC remains relatively stable, but RA shoots off north, disappearing off the graph. I think this happens only when I'm on house AC power and the mount is plugged into a Pyramid PS9KX AC-DC converter. Tonight I will also go back to battery (Jackery 240) and see if that error pops up again. 




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