BACKLASH ADJUSTMENTS

94 views
Skip to first unread message

Richard Brekne

unread,
Apr 19, 2022, 4:36:55 AM4/19/22
to open-phd...@googlegroups.com
Hi 
I am kinda stuck wondering how to proceed with whether I should tighten the dec backlash grubb screws or lossen them. I had them roughly tight without audible binding and guiding assistant backlash measurement failed immediatly..  100 north steps and not enough movement. So I loosened them to just barely no noticeble backlash and the clearing north backlash went ok in 12 steps but it could not establish a steady south movement and I got the attached graph. I should mention I got a good calibration just prior to this and guiding averaged at about 0.8 total rms with both ra and dec roughly the same. Scope was balanced slightly top heavy. 

Looking for a methodic way to proceed. 

Bests
Richard Brekne

20220419_000333.jpg

Brian Valente

unread,
Apr 19, 2022, 10:56:00 AM4/19/22
to Open PHD Guiding
Hi Richard

South movement is not required for a good calibration, and it sounds like you ended up with reasonable guiding. You might consider guiding in one direction in Dec

Regarding your question on proper adjustments, you didn't say anything about the mount model, but whatever adjustments you need to do are specific to your mount. I suggest you find a user group or talk to the manufacturer directly about how to go about removing the backlash

--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/1650357400518.6.16222%40webmail-backend-production-695b5476b4-q5kln.


--
Brian 



Brian Valente

Bruce Waddington

unread,
Apr 19, 2022, 11:18:41 AM4/19/22
to Open PHD Guiding
I agree with Brian, you should probably ask for mechanical help elsewhere.  However, the Guiding Assistant graph you attached doesn't indicate backlash at this point, it looks like you have a lot static resistance on the axis (stiction).  Sources of this include a gear mesh that is still too tight or gross imbalance of the OTA on the Dec axis.  Large Dec backlash doesn't prevent reasonable guiding, over-tightening and stiction usually does.

Good luck,
Bruce

Richard Brekne

unread,
Apr 19, 2022, 6:20:46 PM4/19/22
to open-phd...@googlegroups.com
Thanks ! It is a eq6r.  I get a good calibration and guiding between 0.5 and 0.7 but guiding assistant backlash measurement fails because I cant get enough consistent south movement. I'm still trying very tiny adjustments to the backlash grub screws but with guiding under 0.7 and down to 0.5 I wonder how critical it is to get rid of it..? 

Bests
Richard 


Den April 19, 2022 kl. 4:55 PM Central European Summer Time, skrev Brian Valente <bval...@gmail.com>:
Hi Richard

South movement is not required for a good calibration, and it sounds like you ended up with reasonable guiding. You might consider guiding in one direction in Dec

Regarding your question on proper adjustments, you didn't say anything about the mount model, but whatever adjustments you need to do are specific to your mount. I suggest you find a user group or talk to the manufacturer directly about how to go about removing the backlash

On Tue, Apr 19, 2022 at 1:36 AM Richard Brekne <ri...@pianostemmer.no> wrote:
Hi 
I am kinda stuck wondering how to proceed with whether I should tighten the dec backlash grubb screws or lossen them. I had them roughly tight without audible binding and guiding assistant backlash measurement failed immediatly..  100 north steps and not enough movement. So I loosened them to just barely no noticeble backlash and the clearing north backlash went ok in 12 steps but it could not establish a steady south movement and I got the attached graph. I should mention I got a good calibration just prior to this and guiding averaged at about 0.8 total rms with both ra and dec roughly the same. Scope was balanced slightly top heavy. 

Looking for a methodic way to proceed. 

Bests
Richard Brekne


--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.


--
Brian 



Brian Valente


--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.

Richard Brekne

unread,
Apr 19, 2022, 6:27:10 PM4/19/22
to open-phd...@googlegroups.com
Thanks. I am getting advice on adjusting the eq6r from relevant sources yes, balance and gear mesh are set by using an amp clamp meter so balace is not an issue, but I may still be a hair tight on gearmesh. The axis both move pretty freely so excessive stiction should not be a problem. 

If getting rid of south backlash is not a mandatory then I'll end up leaving it. Guiding is now between 0.5 and 0.7. 

Bests
Richard


Den April 19, 2022 kl. 5:18 PM Central European Summer Time, skrev Bruce Waddington <bw_m...@earthlink.net>:
I agree with Brian, you should probably ask for mechanical help elsewhere.  However, the Guiding Assistant graph you attached doesn't indicate backlash at this point, it looks like you have a lot static resistance on the axis (stiction).  Sources of this include a gear mesh that is still too tight or gross imbalance of the OTA on the Dec axis.  Large Dec backlash doesn't prevent reasonable guiding, over-tightening and stiction usually does.

Good luck,
Bruce

On Tuesday, April 19, 2022 at 7:56:00 AM UTC-7 bval...@gmail.com wrote:
Hi Richard

South movement is not required for a good calibration, and it sounds like you ended up with reasonable guiding. You might consider guiding in one direction in Dec

Regarding your question on proper adjustments, you didn't say anything about the mount model, but whatever adjustments you need to do are specific to your mount. I suggest you find a user group or talk to the manufacturer directly about how to go about removing the backlash


On Tue, Apr 19, 2022 at 1:36 AM Richard Brekne <ri...@pianostemmer.no> wrote:
Hi 
I am kinda stuck wondering how to proceed with whether I should tighten the dec backlash grubb screws or lossen them. I had them roughly tight without audible binding and guiding assistant backlash measurement failed immediatly..  100 north steps and not enough movement. So I loosened them to just barely no noticeble backlash and the clearing north backlash went ok in 12 steps but it could not establish a steady south movement and I got the attached graph. I should mention I got a good calibration just prior to this and guiding averaged at about 0.8 total rms with both ra and dec roughly the same. Scope was balanced slightly top heavy. 

Looking for a methodic way to proceed. 

Bests
Richard Brekne


--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.


--
Brian 



Brian Valente


--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.

Bruce Waddington

unread,
Apr 20, 2022, 4:02:55 PM4/20/22
to Open PHD Guiding
Your guiding and imaging results are all that really matter.  The undesirable Dec behavior may cause extended settling times during dithering or perhaps when the Dec guide direction changes, but you can decide if that warrants trying to make further hardware adjustments.

Good luck,
Bruce
Reply all
Reply to author
Forward
0 new messages