Advice for my setup and mount (EQM-35) - Forums

Topic starter

Dec 2, 2024 · Edited: Dec 2, 2024

As you all probably know, the EQM-35 has notorious DEC issues. I've run into similar problems, mainly when I dither or a cable snag occurs (I'm still working to fix the latter).

As long as I perfect the polar alignment, DEC seems to have no issues. This makes sense since the mount doesn't need to correct much in the DEC if PA is perfect. However, when I dither, the mount takes forever to settle (30-90s) due to considerable backlash and possibly stiction. I've already tried to adjust the backlash but to no avail.

My next steps to try and continue dithering but also mitigate this issue is to

1) Increase the max settle time to 2 minutes just in case it takes that long. I'll also leave the min settle time to around 10.
2) Dither every 4-5 frames.

I've tried dither in RA, but I always get walking noise. My typical exposures are around 120s.

Does this sound good, or does anyone have any other advice?

Thank you in advance.

Well Written Engaging

David Russell

Dec 2, 2024

Trevor I also shoot 2 minute exposure and used to dither every 4 or 5 frames.
\
I noticed that when I changed the dither interval to every 8 frames I could see no negative results in the stacked results.

I shoot lots of subs, sometime 350 or 400 and I THINK the more subs you shoot, the less frequently you need to dither.

experts will advise if I am correct about this, but if I am then perhaps you dont need to dither as often as you are now.

Christian Großmann

Dec 2, 2024

I don't know what software you use. I have an EQ5 Pro and it also has issues with the DEC axis. In the guiding graphs I could see, that it took up to minutes until the mount was able to get the guiding star back to where it was. The backlash was huge and no matter what I tried, I couldn't make it better. But then I set the minimum pulse width in EQMOD to a higher value. Mine is now at around 700ms, which is huge. But it did the job. The mount works well this way and for the equipment I use on it (usually a 350mm Quatruplet APO with an ASI183), it is more than enough.

I had to fiddle a bit with the pulse width. If you set it too high, your mount will keep correcting every pulse in a different direction. If you set it too low, the mount is not able to do a proper correction at all. But if you hit the right spot, it'll be fine. I assume, setting up the gear spacing from the motor to the worm axis will never work as needed unless you have a belt driven solution. The EQ5 is not an high end mount and the EQ35 is neither. It might be very similar to the EQ5. Both are in the same price range.

I don't know, if this is the solution for you, but for me, the difference was night and day.

While imaging broadband, I typically dither every 3 frames because you get so much data. Here I don't see any difference to images I made where I dithered every single frame. With narrow band, you get much less images and you might want to diher every frame. I usually took 20 minute subs and although it's obviously not perfect, a short period of error during guiding has not a huge impact on the final sub, because the signal is already very faint.

CS

Christian

Helpful

Flavio Cicero

Dec 2, 2024

Hi Trevor,

I also have an EQM-35 which I have somewhat tuned myself, and run a Quattro 150 on it (so around 7-8kg total), and get around 0.9" guiding.
If you're having issues with backlash, there are some gears that you can tune yourself by tightening and loosening screws around the gears (hidden by the black boxes). I tuned mine to the point where I can no longer physically feel the backlash when I move my mount head manually, but before it starts grinding.

It's a relatively low risk tweak and can be undone pretty easily if you mess up. Fwiw I can achieve 5+ minute exposures, and dither every 5 frames. Using PEC in phd2 also helps with minimising other backlash effects. I'm not sure what telescope you're using, but stiction only becomes an issue with very heavy payloads (I've run an 8" Newtonian on mine before and had some stiction issues at specific angles). If you have cable snag, that's not really a problem with the mount, but with your cable management.

Flavio

Helpful Respectful Engaging Supportive

Joe Linington

Dec 2, 2024

Full Belt Mod. There is a home brew belt mod that uses 3D printed parts, one replacement motor and the original electronics or the full OnStep treatment that replaces the control box with a much more advanced one and both motors with more accurate and larger ones.

Carefully adjusted the backlash in the worm gear/ring gear isn't usually any worse than any other mount (there are always exceptionally bad ones out there), I have seen guiding as low as 0.6 arcseconds. The main problem, especially in DEC, is the motor is held on with a single bolt and can never stay well aligned with the reduction gears between the motor and the worm gear. This is where the majority of the backlash develops. Fresh off the bench my EQM can sustain better than 1 arcsecond guiding, it slowly deteriorates over a month or so to about 1.2 arcseconds. But move it once and just nudge the DEC motor and all bets are off, suddenly it's a chore to keep it guiding below 1.6 or worse.

I haven't done a belt mod because I have 2 other mounts now that perform much better and much, much more reliably. It's on my list but I keep debating selling the EQM or modding it. I also hate the saddle.

Helpful Insightful Engaging

Trevor

Topic starter

Dec 2, 2024

Flavio Cicero:
Hi Trevor,

I also have an EQM-35 which I have somewhat tuned myself, and run a Quattro 150 on it (so around 7-8kg total), and get around 0.9" guiding.
If you're having issues with backlash, there are some gears that you can tune yourself by tightening and loosening screws around the gears (hidden by the black boxes). I tuned mine to the point where I can no longer physically feel the backlash when I move my mount head manually, but before it starts grinding.

It's a relatively low risk tweak and can be undone pretty easily if you mess up. Fwiw I can achieve 5+ minute exposures, and dither every 5 frames. Using PEC in phd2 also helps with minimising other backlash effects. I'm not sure what telescope you're using, but stiction only becomes an issue with very heavy payloads (I've run an 8" Newtonian on mine before and had some stiction issues at specific angles). If you have cable snag, that's not really a problem with the mount, but with your cable management.

Flavio

I have also tuned it by adjusting the worm gear, but I still get issues with DEC backlash when dithering.

My guiding last week with only RA dither was around 0.7-0.8", but I suspect it to be higher with DEC dithering. I suppose the only real thing I can do is what I said in my post and increase settle time/dither more than every frame.

Trevor

Topic starter

Dec 2, 2024

Christian Großmann:
I don't know what software you use. I have an EQ5 Pro and it also has issues with the DEC axis. In the guiding graphs I could see, that it took up to minutes until the mount was able to get the guiding star back to where it was. The backlash was huge and no matter what I tried, I couldn't make it better. But then I set the minimum pulse width in EQMOD to a higher value. Mine is now at around 700ms, which is huge. But it did the job. The mount works well this way and for the equipment I use on it (usually a 350mm Quatruplet APO with an ASI183), it is more than enough.

I had to fiddle a bit with the pulse width. If you set it too high, your mount will keep correcting every pulse in a different direction. If you set it too low, the mount is not able to do a proper correction at all. But if you hit the right spot, it'll be fine. I assume, setting up the gear spacing from the motor to the worm axis will never work as needed unless you have a belt driven solution. The EQ5 is not an high end mount and the EQ35 is neither. It might be very similar to the EQ5. Both are in the same price range.

I don't know, if this is the solution for you, but for me, the difference was night and day.

While imaging broadband, I typically dither every 3 frames because you get so much data. Here I don't see any difference to images I made where I dithered every single frame. With narrow band, you get much less images and you might want to diher every frame. I usually took 20 minute subs and although it's obviously not perfect, a short period of error during guiding has not a huge impact on the final sub, because the signal is already very faint.

CS

Christian

I'll look into this.

However, if I can get it working with a longer settle time and dithering more than every frame, I'll leave it as is.

Well Written

Trevor

Topic starter

Dec 2, 2024

Joe Linington:
Full Belt Mod. There is a home brew belt mod that uses 3D printed parts, one replacement motor and the original electronics or the full OnStep treatment that replaces the control box with a much more advanced one and both motors with more accurate and larger ones.

Carefully adjusted the backlash in the worm gear/ring gear isn't usually any worse than any other mount (there are always exceptionally bad ones out there), I have seen guiding as low as 0.6 arcseconds. The main problem, especially in DEC, is the motor is held on with a single bolt and can never stay well aligned with the reduction gears between the motor and the worm gear. This is where the majority of the backlash develops. Fresh off the bench my EQM can sustain better than 1 arcsecond guiding, it slowly deteriorates over a month or so to about 1.2 arcseconds. But move it once and just nudge the DEC motor and all bets are off, suddenly it's a chore to keep it guiding below 1.6 or worse.

I haven't done a belt mod because I have 2 other mounts now that perform much better and much, much more reliably. It's on my list but I keep debating selling the EQM or modding it. I also hate the saddle.

I'll look into this. Thanks!

Trevor

Topic starter

Dec 2, 2024

David Russell:
Trevor I also shoot 2 minute exposure and used to dither every 4 or 5 frames.
\
I noticed that when I changed the dither interval to every 8 frames I could see no negative results in the stacked results.

I shoot lots of subs, sometime 350 or 400 and I THINK the more subs you shoot, the less frequently you need to dither.

experts will advise if I am correct about this, but if I am then perhaps you dont need to dither as often as you are now.

I usually plan to go for over 100, but I also want to start doing bigger projects, so the number you specified sounds about what I want to shoot for.

The mount itself guides perfectly (as long as I get good PA and minimal DEC adjustments are required); it's just when a big adjustment occurs (dithering) that it has issues. I'm hoping this will solve my problem.

On my first attempt with this mount, I dithered every frame and accepted the long settle times. I lost about half my imaging session, but the final image turned out really good noise-wise (M33 on my profile).

TiffsAndAstro

Dec 2, 2024

David Russell:
Trevor I also shoot 2 minute exposure and used to dither every 4 or 5 frames.
\
I noticed that when I changed the dither interval to every 8 frames I could see no negative results in the stacked results.

I shoot lots of subs, sometime 350 or 400 and I THINK the more subs you shoot, the less frequently you need to dither.

experts will advise if I am correct about this, but if I am then perhaps you dont need to dither as often as you are now.

I have a GTi and it often seems to take a little while to settle (not every time...) I dithered every 5 frames at 120sec subs.
So I pushed it to every 7 frames at 180sec as a test.
Still no walking noise....

Bass, how low can you go? (Before walking noise etc reappears)