EQ6R pro DEC Backlash Sky-Watcher EQ6-R · Tyking · ... · 12 · 674 · 0

I had some DEC backlash issues with my mount recently, PHD2's Guidegraphs became horrid. So i tried adjusting the backlash, watched a few tutorials and started adjusting, after loosening the bolt on the lower part and tightening the one on the top (To engage the worm gear a bit more) tightened up the other 4 screws and started slewing to check for any binding, while slewing a weird sound kept repeating (Heard in the audio file). I have no idea what is causing it, maybe its slight binding? eq6r DEC slew.mp3

It's hard to tell without seeing the PHD2 logs. But I'd start on the guiding side before messing with the hardware. 

A couple things to consider/reverify:
1. Polar Alignment 
2. Recalibrate PHD2 profile 
3. Run Guiding Assistant at least 8 minutes (to capture complete worm cycle on the EQ6). What are the results/recommendations
4. Ensure guide rates are are the same in PHD2 and EQmod or whatever you're utilizing.
5. Ensure mount USB connection is at the correct baud rate. For ASCOM/EQMod, it likes 115000.

I'd also upload the PHD2 log over to their forum as there's lots of fellow AP astronomers that would be willing to diagnose your log.

Hi,
You most probably went too far and you have a gear binding. This has to be avoided absolutely as it is not good for guiding, for the motors, for the gears, for nothing.
When one tunes the backlash of and EQ6R, you move the worm gear closer or farther to the corresponding bronze gear (there are a lot of ressources on the web explaining and demonstrating as https://www.astro-baby.com/astrobaby/help/rebuilding-the-skywatcher-eq6orion-atlas-mount/eq6-worm-alignment/). As the worm gear, nor the bronze gear are not perfect geometrically (not a perfect cylinder) neither mechanically (axis not exactly at the center), if you move one too close to the other it might happens that on a 360 rotation, the very small play becomes a binding, smooth or stiff and this has to be avoided. So as shown in a lot of videos on this subject (for example, https://www.youtube.com/watch?v=1-jAGnAiuE0&t=12s), each time you do a little adjustment, you tight everything and you run a 180° (at least) rotation of the corresponding axis RA or DEC to check if there is no binding at all (either by listening to a strange noise or using an ammeter). For my EQ6R, I had to balance between reducing backlash and avoid binding and at the end some backlash remains. Some mechanical experts are running the exercice to correct the worm gear and the bronze gear near to perfection but this is another story.
EQ6R are very robust and capable mount but you need to tune them properly to get the best they can achieve.
Hope this helps,
Frédéric

Hi,
Do you have an ammeter, that you can place in-line with the power supply?
At fastest slew, it should be around 1.0 amps.  If it is much higher (1.2 amps or more), that could indicate binding.
Also, did you clean up the gears and swap in "real" grease? (as opposed to what seems like glue, in the original condition).
I like marine lithium (not the clear stuff). Jet lube is good.  Others can comment.

I did this backlash tuning a few weeks ago and had this exact sound. It is defenitely gear binding. All you need to do is to loosen it a bit again, as already mentioned above

Solved this problem on a DM session, thank you all for your input


I too, had this issue up until May of this year. Periodic spikes after an over-correction that resulted in having the DEC hold at 1-2" for minutes on end while guiding.


For future reference, anyone else experiencing DEC or RA backlash that doesn't tune out with grub screws alone, take these steps:

1. Half-turn on the 4 body hex screws of the axis to loosen them

2. Loosen the DEC grub push-pull screws until they are set to be flush with the housing.

3. Align the teeth to a desired position.

4. Tighten the north facing screw, make sure there is no mechanical play in the drivetrain.

5. Tighten the 4 body hex screws slightly, enough to not move the housing under slew, but not enough to not allow the grubs to push or pull it.

6. Slew the axis 180 degrees both directions, while tightening the North grub until slight binding is heard.

7. Tighten the opposing screw to reduce pressure, until slight binding becomes mute. Please ensure that you do not have to tighten this screw all the way down, as you will use this screw in the future to adjust for temperatures depending on the season.

8. Fully tighten the 4 body hexes.

9. Finally, you are going to have to be out with the scope for this step, as you need a reference for backlash and reaction time. 

9a. If you do not have a hand controller, I would use Manual Guide mode in PHD2 to manually slew the axis in small increments, or the SynScan app, Nina, etc.

10. While centered on a bright star, with a fast framerate, slew the axis back and forth at 1x speed, while tightening or loosening the grub screws to fine-tune adjust the backlash. Response time should be instantaneous or as close as possible.

10a. Some mounts have more advanced issues that require different criteria be met to solve, so as long as you can get it as close to zero as possible on your mount without having to open it up, it should be fine.

Hope this helps those who need it in the future,

V.

It's funny, I too have this issue with one of my EQ6s.    It's almost random at times.  It's so rare these days that I don't even bother chasing it anymore.  I feel like the gears have broken in enough to make things run better.     I like your adjustment method tho.   I typically found when this issue happens, I would simply loosen the 4 body screws, hoping to relieve any pressure, then retighten them. It would usually be good for a few nights till the temperature swings.   I'll have to give your method a shot next time I get frustrated.

Oskari Nikkinen:
By the way you should slew a full rotation of the whole DEC axis, there are high and low spots in the gears and its possible you will bind at one of those high spots while most of the time you are fine. The tricky part is finding that high spot and adjusting backlash so that you can clear it.

Agree and the trick is you cannot slew at high speed to check this as it will blow through any slight bindings.  I've settled on an in-line ampmeter and slew at rate 6 watching the meter.  Any areas with binding show as an increase in current.  It's slow.  It's boring.  But it's very effective.  https://www.amazon.com/gp/product/B07Y89632T/

*Yep, this is the right way to do it. I use a clamp multimeter around the positive cable to this and slew at various slow speeds over the high spot. I also use this method to find the best balance for both axis.

Very small differences in balance are easy to see in the increased amps whereas trying to feel them by hand would be close to impossible.