7 replies to this topic

[Phillip_Locke]

Folks,

 

I finally had a chance to mount my 11" Edge SCT on the CEM70 last night.  I wanted to see if it will be realistic to image with a 0.7 reducer on the Edge.  I made sure everything was balanced and it looks like I have an issue with RA spikes that occur in intervals same as the worm period.  Additionally, I mount would sometimes make a bit of a sound when the mount would either start or stop slewing (different from the "normal" noises).  Slightly freaking out, I then mounted my Skywatcher Esprit 100 ED scope to the mount and ran a short guided session.  I was unable to see any of the spikes in this short period.  I routinely guide at around 0.6" RMS with the CEM 70 and the 100mm refractor.  I did tighten the belt on the RA axis last week since it was a bit loose.  I may have tightened it a bit much?  Not sure if an overtight belt could contribute to the RA spikes.  Note that the moon was nearly full and seeing was pretty back last night.

 

I understand that guiding the larger scope is more challenging, but am at a loss for the RA spikes.  

 

Please let me know if you have any experience with this and if you have any suggestions.  I've attached screenshots of the comparisons.

 

Thanks!!!

 

-Phil

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[DuncanM]

You probably have the worm/worm gear mesh too tight or too loose. IIRC, there is a procedure for adjusting it on the CEM70.

[GaryShaw]

Hi Phillip

At one point I had spikes similar to that although they were not quite as regular as yours seem to be. It was quite a while back and it went away without my intervention other than my rebalancing everything. At the time, I concluded it was due to some sort of resonance induced by the winds that evening. I’d suggest you post your log files to the PHD2 Forum where someone will surely have some helpful insights.

Gary

[Phillip_Locke]

Thanks for the help so far:  Here's the link to the guide log: https://openphdguidi...2_logs_dYq6.zip

 

It was a bit breezy and I had the huge aluminum dew shied on the scope at the time.

 

I'll post to the Phd2 forums as well

 

 

Folks,

 

I finally had a chance to mount my 11" Edge SCT on the CEM70 last night.  I wanted to see if it will be realistic to image with a 0.7 reducer on the Edge.  I made sure everything was balanced and it looks like I have an issue with RA spikes that occur in intervals same as the worm period.  Additionally, I mount would sometimes make a bit of a sound when the mount would either start or stop slewing (different from the "normal" noises).  Slightly freaking out, I then mounted my Skywatcher Esprit 100 ED scope to the mount and ran a short guided session.  I was unable to see any of the spikes in this short period.  I routinely guide at around 0.6" RMS with the CEM 70 and the 100mm refractor.  I did tighten the belt on the RA axis last week since it was a bit loose.  I may have tightened it a bit much?  Not sure if an overtight belt could contribute to the RA spikes.  Note that the moon was nearly full and seeing was pretty back last night.

 

I understand that guiding the larger scope is more challenging, but am at a loss for the RA spikes.  

 

Please let me know if you have any experience with this and if you have any suggestions.  I've attached screenshots of the comparisons.

 

Thanks!!!

 

-Phil

[Phillip_Locke]

Thanks for the help so far:  Here's the link to the guide log: https://openphdguidi...2_logs_dYq6.zip

 

It was a bit breezy and I had the huge aluminum dew shied on the scope at the time.

 

I'll post to the Phd2 forums as well

IOptron services is always very responsive; here's what they said:

 

Sorry to hear about the spikes. If the spikes repeat with the same period as the worm, it is like a debris or damage on the worm. You may clean the grease on the worm and see if any dent there. If no damage on the worm, regrease it and try again.

 

This instruction  for worm replacement can be used as a reference for worm cleaning.

https://www.ioptron....Replacement.pdf

[michael8554]

Hi Phillip

 

I agree with the iOptron assessment of grit in the worm.

 

Which just might have gone when you tested with the 100ED.

 

Worth trying again with the Edge !

 

I noticed from the GuideLog:

 

1. You Calibrated at Dec = 61.6 deg

 

You get best results at +/- 20 degrees of Dec = 0

 

2. Your first Cal had a warning   Last Cal Issue = Difference

 

But you guided despite.

 

3. The RA minimum Move is set to about 0.2 arcsecs, which seems very low to me..

 

Which means RA is reacting to the tiniest star twinkle.

 

Was that the Guide Assistant recommendation ?

[Phillip_Locke]

Thanks for the information.  Yes, I was rushing a bit with the guiding parameters.  Also, I used a 400mm f/5 guide scope and I had my 242mm/50mm Evoguide's parameters in PhD2.  

 

I think I'm going to take a crack at opening up the mount and checking/cleaning the worm and gear.

Hi Phillip

 

I agree with the iOptron assessment of grit in the worm.

 

Which just might have gone when you tested with the 100ED.

 

Worth trying again with the Edge !

 

I noticed from the GuideLog:

 

1. You Calibrated at Dec = 61.6 deg

 

You get best results at +/- 20 degrees of Dec = 0

 

2. Your first Cal had a warning   Last Cal Issue = Difference

 

But you guided despite.

 

3. The RA minimum Move is set to about 0.2 arcsecs, which seems very low to me..

 

Which means RA is reacting to the tiniest star twinkle.

 

Was that the Guide Assistant recommendation ?

[Phillip_Locke]

Folks,

 

I took the RA axis apart over the weekend.  I polished the worm to remove a few spots, cleaned and relubed the worm gear and worm, adjusted the worm bearing tension, and adjusted the RA belt tension.  Other than two washers that fit between the worm block and the attachment to the mount, it's really pretty easy.  Much, much easier than doing the same on other mounts I've worked on.  I slewed the mount at bit last evening but weather conditions we not good for guiding check.  I'll have it out tonight and will update - crossing my fingers!!

 

-Phil