Dec backlash

[Padraig]

Hi

does anyone know what might cause this issue with dec. backlash?

 

south steps seem to stall ?

 

 

 

[Ali Alhawas]

Maybe a sticky grease ..

Does the Dec. axis move freely when you move it by hand ? Is there any stiffness in a specific part along around 360 degrees?

Did this symptom in Dec. backlash appeared recently ?

How was your balance ? 

[ollypenrice]

I don't pulse guide but I wonder if this is backlash? If so, running one-side-heavy (as you do in RA to reduce backlash,) doesn't work well because, towards the zenith, the imbalance approaches zero. The usual trick is to run slightly misaligned and guide in Dec in only one direction, the direction needed to correct the misalignment. You find this by trying both then swapping after the flip. It does work reasonably well.

Obviously, if this is caused by backlash then reducing that mechanically is the best bet.

Olly

[Padraig]

7 hours ago, Ali Alhawas said:

Maybe a sticky grease ..

Does the Dec. axis move freely when you move it by hand ? Is there any stiffness in a specific part along around 360 degrees?

Did this symptom in Dec. backlash appeared recently ?

How was your balance ? 

About 2/3 weeks ago I notice that there was some backlash both in ra and dec. this was while I was trying to improve my balance. 
I probably went a bit heavy handed with my adjustments. I backed off the ra meshing a bit , for as far as I know it’s not as critical. 
Then started to fine tune dec backlash which as far as I see on the graph and physically is very slight. 
I had tightened up the floating nut on the dec. and thought this might be the issue. But last night, I had a short window of opportunity to test again with it only very slightly pinch tight.
Following all the manuals for phd2 and Eqmod,  ( yes , actually reading them 😆 ) 

my PA hasn’t been better and happy with my guiding 0.5 -0.7 ish. 
The reason I started to tinker with meshing was to reduce my peak error …which was a bit wild ?

For the short time I had last night, for the most part was 1.0” and the best I’ve seen in target display.
just can’t put my finger on what’s causing this strange graph ? 

I’ll check out your suggestions and get back.
thanks.  

 

Edited December 16, 2021 by Padraig

[Padraig]

11 hours ago, ollypenrice said:

I don't pulse guide but I wonder if this is backlash? If so, running one-side-heavy (as you do in RA to reduce backlash,) doesn't work well because, towards the zenith, the imbalance approaches zero. The usual trick is to run slightly misaligned and guide in Dec in only one direction, the direction needed to correct the misalignment. You find this by trying both then swapping after the flip. It does work reasonably well.

Obviously, if this is caused by backlash then reducing that mechanically is the best bet.

Olly

It’s hard to know it is caused by backlash, I was very careful not to have binding. But tried to reduce as much as possible. The backlash was at around 1000mS but that was when my sidereal rate was set at 0.5 in eqmod. Since then I’ve moved it up 0.9 as recommended by one of the manuals. That’s when my backlash dropped back to ~500mS. Made sense to me, why have phd2 working so hard. Seems to preform better with the limited time I had of clear sky. 

Now unless I went too far with  adjusting …

The idea of slightly misaligned and guiding in one direction and then change after a flip sounds good, because I think read somewhere that can be automated into the sequence. 
 

like us all ,I need a few clear hours. 
 

[Padraig]

Follow up:

Finally,  got one hour of clear sky.

So I had a few things I want to try to help with this issue, first was to retighten the floating nut on dec. and check I hadn't introduce any adverse effects. Next, was to slightly increase backlash, ( not to many out there doing that these days 😁 ) but , no joy. Also checked, had I over tighten clutch, ( grasping as straws). I was starting to think there might be some internal mechanical issue, that would need a strip down to investigate. On that note, what would that involve ?

One final push,

Set up backlash again, but graph looked horrible on "guider assistant" …. gone too far. Backed off till I could slightly hear and feel a backlash while rocking declination. THEN , slightly pinched the "locking Allen keys"  head closest to the worm gear and then locking down the opposite two.

Bingo....as good as it gets.

Hope this of help to others, and thanks to Ali and ollie

PS: ollie, I'll be trying your suggestion in the future but I'm really hungry to gather some subs when this cloudy spell passes

Thanks again.

 

 

 

[Ali Alhawas]

Congrats ! Happy for you 🎉

By the way .. What is your mount model ? age ? 🙃

[Padraig]

As-eq6 pro 

I have it about 3/4 years now. 
Started with 6” Sct but got fed up with dewing up, so jumped over to 130 pds with asi294mc. Which I enjoy but small apo would have been nice. 
Still a lot to learn with so few nights. 
latest project is collimating with my new Concenter 2”. for the secondary mirror. 
I find it quite good for aligning with the focuser. 
I’ll do a star test, then mount Zwo EAF. ( Xmas gift ) or maybe just image since it’s been so long. ???