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Poor guiding and declination axis slipping on belt modded EQ5 Pro.

Sky-Watcher EQ5 Pro Open PHD Guiding Project PHD2 Unspecified/unknown company EQMod Guiding
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Craig Dixon avatar
Craig Dixon avatar
I've recently been given a Skywatcher EQ5 Pro mount that the previous owner has belt modded and I was trying this out on my second setup last night but my guiding was terrible. 
The mount just couldn't correct on the dec axis. here's what PHD2 looked like at the start of the session. I did initially have problems calibrating but when I changed the tracking speed to 0.5 in EQMod, it was able to calibrate. So looking at this screenshot, either there was an error in the calibration or there is something I need to look at in the mount. However, I'm not sure where to start. Has anyone had any issues like this before?

I've also checked the PHD2 log and can see a consistent drift of the dec axis. It looks like PHD2 is constantly trying to correct this but it just slips away again. Here's the full guide log:

PHD2_GuideLog_2024-08-16_201059.txt

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Tony Gondola avatar
Tony Gondola avatar
Have you checked for backlash on the Dec axis? Lock the clutch on the Dec axis and see if you have any play, you can feel it. I don't own that mount but there are videos on YouTube that show in detail how to make that adjustment.
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andrea tasselli avatar
andrea tasselli avatar
Check for slack in the belt connecting the motor to the Dec axis.
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Christian Großmann avatar
Christian Großmann avatar
I own the EQ5 unmodded and had a lot of trouble with backlash. I couldn't solve the issue for a long time. I have to increase the DEC backlash value in EQMOD (lowest slider ander the guide speed). I don't know how the value is in my case, but the slider is set to about 1/4th in my case. Your's is different, of course. The point is, that I was never able to get it right without this setting. Now it works like a charme. If you go too far with this slider, PHD2 is correcting in alternating directions all the time. You will see when you went too far.

But I would check the belt as well. The mods I've seen so far all uses quite short belts and tightening them might be tricky. Also check for loose screws on the parts as well. Setting up the worm gears as in those youtube videos is a good thing to do. It worked wonders on all of my 3 setups (all skywatcher EQs) and increased the guiding performance by at least 30% compared to the factory settings.

I won't say that this is the right solution for your case, but it's at least worth to look at.

CS
Christian
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Craig Dixon avatar
Craig Dixon avatar
IMG_7886.mov

thanks all. I’m guessing that this is a pretty huge amount of backlash
Christian Großmann avatar
Christian Großmann avatar
This is way too much. The axis should not be movable at all by hand. Either the wheel slips across the axis, so you have to tighten the grub screws (usually two of them) in it, or the worm wheel is far too much away from the matching wheel thats on the dec axis. Hopefully, the first thing is the case. Than its an easy fix. If the whole axis turns this way, you need to follow these youtube videos to fix this. Hopefully your worm wheel isn't damaged. But it should have no teeths at all with this amount of play. So I don't think this is the case…

It's crazy how this even can be. But I think its fixable.
Craig Dixon avatar
Craig Dixon avatar
I’ve managed gets the backlash sorted on this now so that’s much better. I’ve now discovered that the belt used is a little too small so I’m going to order a slightly smaller one. I’m grateful that the mount was given to me but it obviously does need a bit of work.

Thanks for the input everyone. my main mount is an EQ6-R Pro and I’ve never experienced any problems with that so ne’er had to adjust backlash. I’ve learned something new today.
Christian Großmann avatar
Christian Großmann avatar
Glad you did. It will be helpful at some point again…
Tony Gondola avatar
Tony Gondola avatar
Great, it's a useful skill in an time when so many people expect to fix everything with software!