Guiding problems

[Guest]

I bet this is not the first time this question has been asked.

I'm just starting with guiding using PHD2. The mount is HEQ5. Dec is quite good but RA is very erratic and I think the problem is with the mount. Dec is very stable with few guiding pulses needed. RA is not too bad for a few cycles then there'll be a big step in one direction. PHD2 corrects it but then there'll be a big step again after a few seconds. It almost looks like there is backlash in RA or stiction maybe. I've adjusted the weights so it should be driving all the time in RA.

I was expecting DEC to be the problem but it's RA. Previously I've done tests over an hour to see how much drift I get without guiding. I take pictures over an hour, say every 5 minutes. Then I Plate solve each picture and plot the RA and DEC values against time. There is some drift in DEC but RA is practically spot on. So it seems that in gross movement RA is ok but there is a kind of random walk superimposed. 

What kind of problems in the mount might cause this?

Cheers

Steve

 

[michael8554]

Hi Steve

Continuing RA error in same direction could be Periodic Error.

Post a GuideLog that has a Cal and some decent length guiding.

Or you can run PGD2 Guide Assistant for a worm cycle, which turns off guiding and plots where RA and Dec are heading.

That will show the amount of PE and the PA error.

Michael

[Guest]

The PE cycle is about 10 minutes on my mount but the variations seemed faster than that but anyway I'll give it a go.

Steve

 

[wimvb]

9 minutes ago, woodblock said:

The PE cycle is about 10 minutes on my mount but the variations seemed faster than that but anyway I'll give it a go.

Steve

 

You can have stiction/backlash/binding in the gear box. Even belts which don't have proper tension, can cause guiding problems (in case you have a belt modded mount).

[Clarkey]

As Wim says it could be stiction or binding. On my HEQ5 there was a very fine line on the worm gear float between removing backlash and getting binding. Even a quarter turn on the adjusting screw can make all the difference.

[Seelive]

If you're not using an OAG also consider differential movement between the imaging and guide scopes?

[wimvb]

If you need help with specific problems, and not just general tips, you really need to provide us with a guide log. I can also recommend phd log viewer.

https://openphdguiding.org/phd2-log-viewer/