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Perfect polar align and still oblong stars.

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29 replies to this topic

#26 Kevin_A

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Posted 18 June 2019 - 12:00 PM

I had a similar but not quite the same issue with my Star Adventurer until I took it apart and found out that it had 2 issues.

 

My polar alignment would be great then 15 minutes later it was off.... rinse and repeat.

 

1.) the worm gear mesh was slightly too tight (adjustable with hex key)

 

2.) the grease that was inside was too thick causing drag. I checked this when the clutch was loosened and rotation was dragging and wasn't as smooth as it should have been with a balanced payload. I de-greased some of the internals and applied a very very sparing amount of superlube strategically and it spins really easy now.

 

So the combination of a tight worm gear with internal stiction caused the polar alignment to constantly fall behind and off its mark.... repeatedly.



#27 Michael Covington

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Posted 18 June 2019 - 12:39 PM

How did a worm gear problem change the direction in which the polar axis was pointing?



#28 Kevin_A

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Posted 19 June 2019 - 06:47 AM

didn't change direction but my position was behind (slowed down from where it was supposed to be) when checking alignment with polar alignment software so i had to adjust and my stars were no longer oblong once i fixed this... can't say which was the bigger issue other than it would not be in the correct polar alignment position relative to the software location and the thick grease may have caused it to stick then move and almost creating double stars. All I know is when I fixed these 2 issues my stars were no longer oblong.... LIKE I SAID IN MY FIRST LINE OF TEXT.... similar but not the same.... cheers.



#29 Kevin_A

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Posted 19 June 2019 - 06:54 AM

Fyi... if a worm gear has too tight a mesh or parts have internal stiction.... it can cause very weird results from high and low spots on the worm. I design machines with gears and have every day for the last 15 years so its not new to me.



#30 Howie1

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Posted 20 June 2019 - 01:11 AM

Hope you find the issue amongst all the suggestions.

 

If you want to eliminate your polar scope and polar alignment to help narrow it down to one of the other possible issues, then once you've done your PA next time ... just "drift" with a star and see if it wanders over ten minutes or so. Or you can google and read up the method I use called DARV. I'm not saying to use it to actually polar align in your case. Just use it after doing your normal Polaris polar align to check that you really are spot on with your alignment. The image below is one of two done (one pointing low in the East and one pointing at 0 degree DEC up at the Meridian). Only takes 80 seconds to check each adjustment - AZ and ALT.

 

To do this on a star adventurer set 80 second exposure. For the first 10 seconds have the tracking rate button on normal tracking rate to "burn" a bright starting-point "dot". Then turn tracking off (one step turn clockwise of the tracking knob) and let the stars drift for 30 seconds. Then turn the tracking rate to 2x rate for 40 seconds. This will catch up and "drive-past" the stars a bit to enable you to judge better if you really are spot-on with your PA.

 

Photo below shows the end result when polar aligned (just remember you have to do it twice ... once for ALT and once for AZ). The image shows the star trails directly overlying each other almost perfectly intersecting the initial bright-starting-point "dot" ... so I am polar aligned in ALT in this case. If I wasn't then the two lines would form a "V" with the line no longer passing through the initial bright-starting-point "dot".

 

If you find you are indeed perfectly polar aligned from using your polar scope then you know it's something else going on.

 

DARV screenshot

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