SkyWatcher EQ3-2 + PHD2

[Grumman]

Hello all,

I have a SkyWatcher EQ3-2 GoTo mount connected to PHD2 via EQMOD and is giving me a wired declination backlash error on the Guiding Assistant.

Is this a hardware issue (i.e. gear meshing on the mount etc.) or can it be rectified via software?

I have performed the Backlash Clearing Calibration as suggested but did not improve the situation....

Any help would be much appreciated!

 

Regards,

Thanasis

[wornish]

Your polar alignment error ( > 10 arc-minutes)  is very large and that is certainly not helping.   

[RolandKol]

I do not think you have any problems with the mount. Mine NEQ6 backslash graph looks similar.

Invest time into Polar Alignment with prior balancing as 22arc-min PA error is very large. You can do better even without seeing Polaris

Also, give PHD2 a try to pick a star automatically (ALT+S), it looks like you chose a very dim one.

If you do see Polaris, the simple SharpCap polar alignment tool will give you a very nice start for a Drift Alignment Procedure in PHD2.

[Stub Mandrel]

I was able to improve the DEC backlash on my NEQ3-2, but it included regreasing it and adding thrust bearings...

I give no attention to PHD2's PA calculation.

[michael8554]

PHD2 Backlash Comp won't cope with a 23.5 second backlash !!

Worth looking at the Dec worm adjustments.

Even then, get your PA down to about 5 arcmins with the PHD2 Drift Align, and balance so that the dec motor is always pushing away from that slight dec drift, hopefully not having to reverse. Set Min Mo slighly higher.

[Grumman]

Thanks for the helpful replies, I appreciate it! 

I will try to get a better polar alignment next time and try to do this again.

[Grumman]

Hello,

 

I managed to do a good polar alignment and also re-done the calibration.

There is small improvement but there are still 16 seconds of backlash!

Another issue I am experiencing is that for some reason (possibly backlash) the DEC axis suddenly does erratic moves and it goes off the charts literally!

There is no dithering involved or anything, it just suddenly as it is tracking steadily, it just jumps!

I have attached some screenshots as well.

 

Any ideas?

[michael8554]

Did you balance dec to be heavy in one direction?

It appears to be "floating", so is free to move in either direction, so as soon as it has finally corrected one excursion it falls the other way, due to the looseness of the dec drive.

If you increase Min Mo, and with heavy balance, your good PA should allow dec to  freewheel without the need for any, or very few, corrections :->

Another thing, what guide rate are you using? Increasing to 80 or 90% and recalibrating will give Dec a higher ratio, equals faster movements, equals quicker correction !

Your star SNR is yellow, indicating borderline quality ?

Michael

[Grumman]

9 hours ago, michael8554 said:

Did you balance dec to be heavy in one direction?

It appears to be "floating", so is free to move in either direction, so as soon as it has finally corrected one excursion it falls the other way, due to the looseness of the dec drive.

If you increase Min Mo, and with heavy balance, your good PA should allow dec to  freewheel without the need for any, or very few, corrections ?

Another thing, what guide rate are you using? Increasing to 80 or 90% and recalibrating will give Dec a higher ratio, equals faster movements, equals quicker correction !

Your star SNR is yellow, indicating borderline quality ?

Michael

Thanks for the reply Michael !

 

Yes, I did balance DEC to be heavy in one direction.

The guide rates and generally all my EQASCOM settings are identical to this guide.

https://github.com/OpenPHDGuiding/phd2/wiki/EQASCOM-Settings

In regards of the star, i did change the camera settings and got Green SNR on the star but it had the same behavior.

Another thing is that when all the clutches are tight, it seems that the DEC has a small "play" of around 1-2mm -  I think this might be the issue...

 

Regards,

Thanasis

[Stub Mandrel]

1 hour ago, Grumman said:

Another thing is that when all the clutches are tight, it seems that the DEC has a small "play" of around 1-2mm -  I think this might be the issue...

That's probably it, and is likely to be backlash in the gear train or at the worm wheel.

[Grumman]

Thank you Neil!

To be honest, it did not affect any of my 120sec subs nor my 300sec subs I took;  all seem to be fine to be honest...

https://www.skyandtelescope.com/online-gallery/orion-nebula-m42-taken-from-my-light-polluted-front-yard/

I was just curious on why the spikes are there and now I know!

Thank you!

[michael8554]

That EQASCOM guide is spot on, just your dec gear mesh to sort then.

But if you're happy with what you have, not much more to suggest.

Michael

[Stub Mandrel]

How could I forget this thread?