Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Awful DEC backlash IOptron CEM25p

  • Please log in to reply
6 replies to this topic

#1 rocketjake5

rocketjake5

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 24 Sep 2020

Posted 13 June 2021 - 03:07 PM

Hello,
My ioptron mount has been giving me such pain. It guides great in RA, <.50 RMS. But the DEC axis is plagued with terrible backlash causing my stars to elongate. The guide graph in PHD2 has a saw tooth pattern just like some other users have reported. I have yet to identify the source of backlash. The mount is now sitting on my work bench in pieces as I am attempting to solve this for good. Does anyone have any experience with the Ioptron CEM25p and its notorious DEC backlash?

I have adjusted the tension on the belt drive so that it flexes no more that 3mm as recommended by iOptron. Still, DEC guides badly. The worm drive is rock solid in its housing and the pulley grub screw is tight. There is no play in the DEC when I rock the saddle by hand which tells me that the gears are meshed properly.
I am not sure what more information to include. Please help my poor mount :)

#2 rgsalinger

rgsalinger

    Cosmos

  • *****
  • Moderators
  • Posts: 8,800
  • Joined: 19 Feb 2007
  • Loc: Carlsbad Ca

Posted 13 June 2021 - 03:15 PM

The first thing that I would advise doing is to put an eyepiece in and using the hand controller see for sure that it's the mount and nothing else. Elongated stars can come from many different issues.  U

 

sing PHD's backlash calculator conflates all of them into one often useful number.

 

Your mount is belt driven and if the mesh is properly adjusted backlash is going to be negligible. Try a manual star test before doing anything else. 

 

It would be useful to post a picture of the system and a PHD guiding log. Maybe there's something that you are overlooking. 

 

Rgrds-Ross



#3 bips3453

bips3453

    Mariner 2

  • *****
  • Posts: 298
  • Joined: 05 Mar 2020
  • Loc: MN

Posted 13 June 2021 - 05:00 PM

Even if Dec backlash is there, it shouldn't matter with a good PA...

 

Edit: This may not be true in all cases, Thanks Michael! 


Edited by bips3453, 14 June 2021 - 06:48 AM.


#4 rocketjake5

rocketjake5

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 24 Sep 2020

Posted 13 June 2021 - 05:20 PM

The first thing that I would advise doing is to put an eyepiece in and using the hand controller see for sure that it's the mount and nothing else. Elongated stars can come from many different issues.  U

 

sing PHD's backlash calculator conflates all of them into one often useful number.

 

Your mount is belt driven and if the mesh is properly adjusted backlash is going to be negligible. Try a manual star test before doing anything else. 

 

It would be useful to post a picture of the system and a PHD guiding log. Maybe there's something that you are overlooking. 

 

Rgrds-Ross

I will post a snap of my guide graph if its clear soon. Maybe my settings in PHD are way off, but I know for sure that the DEC has backlash because I have performed the cross test is PHD. I just put the mount back together--will see if I did something right.



#5 jesco_t

jesco_t

    Vostok 1

  • -----
  • Posts: 129
  • Joined: 23 Jan 2020
  • Loc: Hamburg, Germany

Posted 14 June 2021 - 03:05 AM

Unidirectional guiding might help you if backlash is really the issue. If you guide only north or south (depending) this will avoid direction reversal and will hide the backlash. Your mount might still guide okay this way.

 

Jesco



#6 michael8554

michael8554

    Apollo

  • -----
  • Posts: 1,075
  • Joined: 19 Aug 2020
  • Loc: Wiltshire UK

Posted 14 June 2021 - 05:49 AM

Even if Dec backlash is there, it shouldn't matter with a good PA...

Good PA means Dec should only require infrequent corrections,

 

But if Dec balance is "perfect", the slightest wind or cable tug will send Dec wobbling between the extremes of the Backlash.


  • bips3453 likes this

#7 rocketjake5

rocketjake5

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 24 Sep 2020

Posted 14 June 2021 - 06:36 PM

Had a clear night. The DEC backlash is a lot better :)
My DEC was still oscillating while guiding, so I changed some settings in PHD. Doing that really improved my guiding and minimized the saw tooth pattern.


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics