PHD2 Guiding Problem

[ItsEricJones]

My guiding used to be flawless but after a month of no clear nights I come back and its tracking like this. Don't really understand why, any suggestions/tips?

[symmetal]

It looks like your polar alignment is significantly off by the rapid rise in Dec error (the rising red line) and a significant amount of Dec backlash too. The Dec corrections are having no effect as they are just driving the mount over the backlash gap. Eventually the teeth engage and the large corrections drive the Dec back in but overshoot as the corrections will lag behind the actual error by the exposure time. The Dec corrections reverse again but just drive it back over the backlash gap again so has no correction effect. Before it's taken up the backlash the polar error Dec drift has again made the Dec error positive. The corrections again reverse over the backlash gap until the teeth eventually re-engage. The cycle then repeats.

Your best options are to reduce the Dec backlash gap if possible by adjusting the mount (you don't say what mount you have) and to get a closer polar alignment to start with. 

Alan

[alacant]

Hi. Not enough data to give an accurate diagnosis -it looks as if it's about to settle- but the DEC aggression at such a low value is never gonna correct that amount of backlash. Did you run the guiding assistant (GA) to arrive at those figures? If so, remember that conditions may vary -a lot- between sessions.

I wouldn't start adjusting anything until you have run the GA again -for at least 10 minutes- and accepted its values.

HTH

[FaDG]

While it's best to have a much smaller backlash, it's not always possibile, nor advisable sometimes (depending on mount manufacturing) to fully dial it out. A different approach could be to induce a very small PA error, so that you have a LOW dec drift only in one direction, then setting a  low Dec threshold (not to show a big sawtooth) and gentle Dec aggressiveness (to avoid overshooting). 

This should do the trick. 

Fabio

[FaDG]

BTW, you don't mention what setup you use... What mount is it? 

[ItsEricJones]

On 23/02/2019 at 03:11, FaDG said:

BTW, you don't mention what setup you use... What mount is it? 

Thank you for your response! This is a Celestron AVX mount, the guiding camera I am using is a zwo asi 120mm with a 60mm guide scope. I am still having problems with the guiding as the rms is around a 3 or 4.

[FaDG]

Yes 3-4 is a lot. 

With a 60mm + ASI120MM my HEQ5 runs at 0.5arcsec on each axis on nights of good seeing. 

Have you tried to increase aggressiveness around 60-70 and induce a small dec drift, let's say 1 arcsec every 5 - 10 seconds? 

[alacant]

4 hours ago, ItsEricJones said:

I am still having problems

Hi. What did the guiding assistant recommend?

Cheers

 

[michael8554]

Guidescope focus could be improved, HFD 4 would be better.

You can see in your graphs that there are no Dec corrections until Dec has wandered off for about 10 secs !

So that suggests speed up exposure to say 1.5 seconds,  reduce MinMo, increase Aggr, until you get a faster response, but not so much it overshoots.

Faster exposure will have repercussions on RA of course, tweek accordingly.

Also have you tried  Alan and Fabio's suggestions to improve dec :

Perfect PA so dec correction mostly not needed,  balance to take up the slack.

Slight PA offset, balance so Dec moves in the direction of offset, and guide in one direction to correct that small drift.

 What were the results ?

It has been very windy recently. 

Michael