3 replies to this topic

[Yomamma]

I have been testing my guiding with a WD20 mount and have read that these mounts use a fairly robust robotics servo motor on the DEC and RA axis.  They are advertised to have little or no backlash.

 

I run PHD2 for guiding and after I calibrate I run guide assistant.  Polar alignments are always around 1 or less but I get all kinds of recommendations for backlash.

 

My rig is an Esprit 100 with OAG and ASI183 camera on the back.  No dangling wires or large objects hanging off the side. Total weight is around 23 pounds and I balance it on my island top with a 2 foot long piece of 2" PVC pipe. I set the rig's mounting plate on top of the pipe and roll it back and forth until I find the balance point then mark it.  When I put the scope on the mount I make sure the marked balance point is in the center of the DEC axis.

 

My gain is set to 70 and exposure time is .5 seconds with an ASI174mm mini guide camera.

 

I can run the same setup back to back and get backlash recommendations from 100ms to 1400ms...lol.

 

What I have done is just guide and then tweak the backlash parameters and watch the results.  I believe I currently use about 30ms of backlash which seems to be almost negligible..

 

My guiding was around .5 - .6  which I thought was not bad given the seeing was not good as I could tell my best FWHM scores for my camera in Sharpcap(measured in pixels) were in the low 4's and I can usually get in the low 3's with good seeing.  My FWHM scores in PHD2 were anywhere from 1.5 to 2.5 it was bouncing around a little.

 

Do any other WD20 users apply backlash compensation and if so how much.

[dswtan]

Dupe? Maybe sensible to post to the main thread here:
https://www.cloudyni...rpastron-wd-20/

 

Your previous:

https://www.cloudyni...on-for-guiding/

https://www.cloudyni...tuning-and-use/

 

FWIW, I just follow what the Guiding Assistant tells me. I've no idea what the BC value is at this point. The biggest transformation for me was moving to 0.5 sec exposures from 1 sec. I'm now reliably seeing ~0.4" or better, which is by far better than any of my (too many) other non-premium traditional mounts (Celestron, Losmandy, iOptron). Very happy!

 

I do now need to watch out that I have at least one half-decent guide star. The Whale/Hockey Stick has been particularly dim for guide stars. I needed to increase the SNR setting to max (200) to ensure PHD2 was not choosing too-dim guide stars. I'm on an OAG at 910mm f/l and ASI220MM Mini. I will swap with a 174 soon to try to help.

 

PS. Checked: my BC is enabled at 20, min 20, max 270. This is slightly different to my previous settings posted in my gallery. But again, I'm just going with the GA recommendations, habitually. Same with the Algorithms. But at this level of guiding performance, I'm not too interested in further tuning interrupting my imaging time. I'm not convinced the BC settings do much here on these mounts.
 

 

 

Edited by dswtan, 27 March 2025 - 01:00 PM.

[calypsob]

You can manually measure backlash on a focuser with a dial indicator by counting steps from a zero point. I wonder how this could be exercised on an eq axis

[rgsalinger]

Run a star cross test. That's the easiest way to see if there is significant backlash.