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ZWO EAF doesn't return to correct position

ZWO EAF Focuser Troubleshooting Help Needed
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Keith Geissler avatar
Keith Geissler avatar
I am having an issue with my ZWO EAF on my Apertura Carbonstar RC6. The focuser doesn't return to the same position when moving. I noticed this in nina as my focus point keeps getting a lower step position than the time before.

To try and fix, I open the ZWO EAF driver, moved the focuser all the way and set the position to zero. Then moved to my normal focus position, which is about position 11000. that is at the 1" spot on my actual focuser. I then moved the focuser via the driver to 13000 and back to the original 11000. However, it doesn't return to the same spot. It is always about 200-300 focuser steps short. So I need to use the driver and move a the focuser in about 200-300 steps to get back to the correct position.

I have tried calculating backlash and putting that number in the driver with no success (i got the same result). I tried several backlash numbers between 100-255 and got the same result. Can you help? is my eaf defective?
Richard avatar
Richard avatar
Definitely start with watching the below tutorial by Patriot Astro and remember to set backlash compensation to Overshoot and not Absolute. You only need to put backlash compensation in one direction (ie IN or OUT) and not both, so adjust one and keep the other set to 0.

https://youtu.be/lHrfaR7A0L0
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Brian Puhl avatar
Brian Puhl avatar
Your EAF is slipping.  

The grub screws on the collet are likely not tight enough. If that doesn't work, check to make sure the friction is tight enough on your focuser.
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Keith Geissler avatar
Keith Geissler avatar
Brian Puhl:
Your EAF is slipping.  

The grub screws on the collet are likely not tight enough. If that doesn't work, check to make sure the friction is tight enough on your focuser.

I have the grub screws as tight as i can get them and the friction knob is also quite tight.  I also took the EAF off to make sure I could turn the focuser manually.  That worked and I reattached the focuser.  It is always about 200-300 steps off on the return.
Rick Krejci avatar
Rick Krejci avatar
Maybe there is some slipping of the connection between your scope and EAF.     I wouldn't mess with the backlash setting in the EAF driver (in the EAF equipment "gear" setting) if that's where you are putting those numbers in.   Leave that one at 0 (or at least no more than 30-40) and just use Nina's Overshoot compensation method and use like 300-400 on one direction only.
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Keith Geissler avatar
Keith Geissler avatar
Rick Krejci:
Maybe there is some slipping of the connection between your scope and EAF.     I wouldn't mess with the backlash setting in the EAF driver (in the EAF equipment "gear" setting) if that's where you are putting those numbers in.   Leave that one at 0 (or at least no more than 30-40) and just use Nina's Overshoot compensation method and use like 300-400 on one direction only.

Is there anyway to test the overshoot setting without doing an autofocus?
Rick Krejci avatar
Rick Krejci avatar
Keith Geissler:
Rick Krejci:
Maybe there is some slipping of the connection between your scope and EAF.     I wouldn't mess with the backlash setting in the EAF driver (in the EAF equipment "gear" setting) if that's where you are putting those numbers in.   Leave that one at 0 (or at least no more than 30-40) and just use Nina's Overshoot compensation method and use like 300-400 on one direction only.

Is there anyway to test the overshoot setting without doing an autofocus?

I just needs to be a number way above (like double or more) what you think the backlash is.   It doesn't matter as long as it washes out the backlash.   Just don't have it fight the driver "gear" backlash setting which is why I suggest setting that to 0.   

I generally figure out my approximate backlash by observing the fine focus know when I reverse direction (with no backlash compensation set anywhere).   Once the knob starts moving, that's about your backlash.   Then overshoot by a lot more than that (at least double, I do 3-4x) and you're good.

You can try backing down on it during a session until you see the curve look wonky (flat on one side), but it's easier just to leave it a large value if it works.
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Keith Geissler avatar
Keith Geissler avatar
I think I may have found the issue. Right around the focus point of my focuser. I noticed it would stick as it tried to rack in. I found the snag and it seems to be working now.  I will test more when I can auto focus a few times
Brian Puhl avatar
Brian Puhl avatar
Sounds like a winner to me.            If it was a backlash issue, you'd simply miss focus point, but the focus point shouldn't be shifting like you were seeing.    Do you think the snag was it skipping a tooth maybe?
Keith Geissler avatar
Keith Geissler avatar
Brian Puhl:
Sounds like a winner to me.            If it was a backlash issue, you'd simply miss focus point, but the focus point shouldn't be shifting like you were seeing.    Do you think the snag was it skipping a tooth maybe?

not sure what it was.  I removed the eaf, and manually turned the focus knob and it still stuck.  I removed the focuser from the scope and it worked fine. I put it back on and it still appears to work.  Go figure.