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PHD2 guiding calibration error

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#1 SStanford

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Posted 23 January 2021 - 03:12 PM

Hi All,

 

Lovely clear night tonight; first opportunity to use my ZWO ASI120mm which I recieved this week.

 

Connected the EQ3pro Synscan to my comuter, controlled by Stellarium, slewed to a star in the South (which then starts tracking), Set-up PHD2, got a good focus on the stars, calibration running smoothly until it "steps north".

 

PHD2 "steps east" (around x50), backlash (around x20) then "steps north" (around x60) before I get "Calibration failed" in the bottom left and the message: "Dec calibration failed: Star did not move enough".

 

At the backlash stage on PHD2 the mount starts clicking every so often, as it does for the whole "steps north" process too 😬.

 

I tried slewing to different parts of the sky but encountered the same failure three times.

 

I'm completely stumped with this one so any guidance would be hugely appreciated! I've attached a screencap of the interface below in case theres anything I've overlooked here.

 

Capture 3.PNG



#2 Tapio

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Posted 23 January 2021 - 03:20 PM

These mounts often have backlash problems.
It might need mechanical tweaking.
But in the meantime you could try setting backlash compensation IN PHD.
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#3 barbarosa

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Posted 23 January 2021 - 03:22 PM

Did you read the instructions re: calibration failure and check or do everything suggested?

 

There is a log file created and it may help if you attach it.


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#4 sbharrat

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Posted 23 January 2021 - 03:31 PM

I had same problem recently. For me, I was using EQMOD to control the mount. Someone pointed out that the default EQMOD setting for guide steps was 0.1 for RA and DEC. Once I changed that to 0.7 sideral rate, my calibration problem went away. 

 

PS: the guide log was helpful for people to help me out. Suggest you include that...


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#5 SStanford

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Posted 23 January 2021 - 05:19 PM

These mounts often have backlash problems.
It might need mechanical tweaking.
But in the meantime you could try setting backlash compensation IN PHD.

Thanks for this.

 

are you able to provide a guide for mechnically tweaking the EQ3? How do I go about setting backlash compensation in PHD?

 

Did you read the instructions re: calibration failure and check or do everything suggested?

 

There is a log file created and it may help if you attach it.

Thanks Barborosa.

 

This is a new one to me; I'll read and action accoridngly.

 

A copy of the log is below:

 

https://openphdguidi...2_logs_b2VW.zip

 

 

I had same problem recently. For me, I was using EQMOD to control the mount. Someone pointed out that the default EQMOD setting for guide steps was 0.1 for RA and DEC. Once I changed that to 0.7 sideral rate, my calibration problem went away. 

 

PS: the guide log was helpful for people to help me out. Suggest you include that...

Thats excellent, I'll gove this a shot tomorrow.

 

log is here:

 

https://openphdguidi...2_logs_b2VW.zip



#6 Tapio

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Posted 23 January 2021 - 06:23 PM

I'm sure someone who uses this mount can give you instructions/links how to tweak the mount if necessary.

 

Here's a link for PHD backlash compensation

https://openphdguidi...#Algorithms_Tab



#7 barbarosa

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Posted 23 January 2021 - 07:18 PM

Now that you have the logs, the best place to ask for help might just be the PHD forum. if you can't find the answer here.

 

Things from your logs-

 

"pixel size = 3.8 um" might be wrong. i think it should be 3.75.  Also "Pixel scale = 6.45 arc-sec/px" and , Binning = 1, Focal length = 120 mm" Is 120mm the correct focal length?



#8 AZ Maverick

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Posted 23 January 2021 - 07:19 PM

The main cause of the 'star did not move enough' error is because the 'ASCOM Pulse Guide Settings' in EQMOD are still set at the default rate of .1.

Make sure you change both the DEC and RA rates to at least .5 (I have mine set at .9).

 

 

Attached Thumbnails

  • GuideRate.jpg


#9 SStanford

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Posted 24 January 2021 - 08:09 AM

I've set RA & Dec rate to x0.80. Does it really matter if I were to put this up to x0.90? would guiding be more accurate at x0.50 for example?
 
"sideofpier" is set correctly to "Pointing ASCOM" as is Guiding "ASCOM pulse guiding".
 
I have also ensure that focal length and pixel size is accurate for the guide scope and cam in PHD2 (3.75 and 120mm (here)).
 
At next clear night I'll be focusing on a portion of the sky +/- 20deg from 0dec and near the meridian. I'll also be slewing north via EQMOD at slew rate 1 for 20 seconds before running calibration.
 
Should this not resolve the issue I'll be trying all the details outlined here and here. I'll post my results after.



#10 DelboyK

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Posted 24 January 2021 - 08:35 AM

I'm sure someone who uses this mount can give you instructions/links how to tweak the mount if necessary.

 

Here's a link for PHD backlash compensation

https://openphdguidi...#Algorithms_Tab

Here’s what I did...

 

The image below shows the Declination drive motor, I took the cover off & noticed the gear wheels were making contact but not 100% parallel with each other. I loosened the bolt circled in red then pushed the Declination drive motor into the gear wheel on the mount, made sure it was parallel and then held it like that while tightening up the bolt again. You can do the same for RA. & an extra bit of grease never hurt

 

I’m sure there’s more you can do but guiding is kinda working well, image also below

 

med_gallery_341644_15765_419600.jpeg
med_gallery_341644_15765_1019621.jpeg


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#11 SStanford

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Posted 24 January 2021 - 09:37 AM

Here’s what I did...

 

The image below shows the Declination drive motor, I took the cover off & noticed the gear wheels were making contact but not 100% parallel with each other. I loosened the bolt circled in red then pushed the Declination drive motor into the gear wheel on the mount, made sure it was parallel and then held it like that while tightening up the bolt again. You can do the same for RA. & an extra bit of grease never hurt

 

I’m sure there’s more you can do but guiding is kinda working well, image also below

Thats excellent, thanks @DelboyK.

 

I notice you're using an 80ED on the EQ3. I assume you're exceeding the 5kg recommended weight limit on the mount, how good are your exposure times?

 

I only ask as I have my eye on the 72ED for the EQ3 due mostly to the fact it's a lightweight scope.
 


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#12 DelboyK

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Posted 24 January 2021 - 10:15 AM

Thats excellent, thanks @DelboyK.

 

I notice you're using an 80ED on the EQ3. I assume you're exceeding the 5kg recommended weight limit on the mount, how good are your exposure times?

 

I only ask as I have my eye on the 72ED for the EQ3 due mostly to the fact it's a lightweight scope.
 

At the moment everything weighs 4.5kg, that includes the 80ED with a guide scope, ASI120mm guide cam & Canon 1000D. I am pushing it to be honest but I've spent a lot of time reading up & understanding things, getting good balancing, getting good polar alignment. I think I'm ok to stick with the EQ3 for now.

 

I've got reasonbly good guiding & good exposures, I tried out 180s guided exposure last night & the stars were all circular, no real elongated stars. Still to try out longer exposures but the next few months may be spent learning about guiding & set up conditions for imaging.

 

Google drive link for the 180s exposure 
 

I posted on this forum earlier today, about guiding & the EQ3 performance, has obvious Dec backlash issues but guiding appears ok-ish


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#13 SStanford

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Posted 25 January 2021 - 04:21 PM

Calibration successful! thanks for your help all. Brief opportunity before the clouds rolled over tonight.

 

With one issue resolved, two more pop up. All part of the fun.

 

1. I ran the guiding assistant tool and had two different outcomes. The second outcome was worse having tweaked PA via the Drift alignment tool (reducing recommeded exposure times from 2-4 seconds to 1-3 seconds , unacceptable!) It also recommended amending the RA and Dec min move, before I apply these changes has anyone had any experience with these amendements?

 

2. The drift alignment tool is very tricky to manage. I had c.40 mins to play with Azimuth adjustment; when I got anywhere near a stable Dec line in the graph, the slightest adjustment in the Azimuth would cause the graph to give a wild reading.  In fact, the lowest PA error I could get was 4.64' (38px). Any tips with this?



#14 barbarosa

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Posted 26 January 2021 - 05:25 AM

I've found that SharpCap polar alignment tool to be easy, fast and accurate. just the tool alone is worth the £10 for a 1 year license. I ignore the alignment numbers in PHD2.

 

The guiding assistant works pretty well. it helps to let it run longer than the minimum time so that you get one or more full revolutions of the worm.




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