The strangest guiding problem ever seen

[jimao22]

Hi

Last night I encountered a problem I cannot find the origin. I am using an EQ6 mount/belt drive/EQMOD, using for guiding an OAG TS 9mm combined wityh a QHY5II-L mono (a very good combination).

The guiding graph is attached bellow. It seems like the both axis were linked in the motion, so I had an error motion like a diagonal. I tried to fix this by recaliibrating the guiding, by slewing over the meridian back and forth, reducing the exposure time for guider from 4 to 2 seconds, but nothing.

Have anyone any idea about what is happens?

[wuthton]

If your mount is pointing somewhere close to North and the motors are driving both axes, it must be software.

Have you somehow flipped your camera feed, it looks like phd is correcting in the same direction as the error.

[Thalestris24]

Hi

I can't say what's causing that and I've no experience with oag's... However, it looks like something fundamental going wrong. Maybe you could try running with guiding off and see how the mount behaves and what the logs say. Presumably it's been behaving ok previously - has anything changed?

Hth

Louise

[ollypenrice]

My first brief encounter with PHD2 saw it guiding in the wrong direction - ie sending corrections in the same direction as the error. As stated above, you seem to be getting this. I normally guide in Astro Art where you can click to invert x and y to rectify this situation.I expect you can do likewise in PHD2 but I haven't looked into this yet.

Olly

[JohnC64]

I've had this, when setting up and calibrating phd on one target and then slewing to another section of sky and starting guiding again.  The trick i found was to always tick the 'force calibration' box in the Brain when moving to a new target.

HTH John

Edit:.  Just reread the OP and you did recalibrate.  Not this then

[jimao22]

Normally, the first graph should look like a shoot target, with random points around the center, a Gaussian distribution.

What I have is extremely strange, because as you see, we have a straight line, right trough the center of the graph, 45 degree slope. I cannot imagine what phenomena could generate this... 

[Thalestris24]

Normally, the first graph should look like a shoot target, with random points around the center, a Gaussian distribution.

What I have is extremely strange, because as you see, we have a straight line, right trough the center of the graph, 45 degree slope. I cannot imagine what phenomena could generate this... 

Hi again

So has it worked ok previously? If so, then something must have changed / gone wrong since. Are you using PHD2? If so, this doesn't require re-calibration between different parts of the sky though you need to ender the DEC value you do the initial calibration at. What do the logs show?

Um, I take it your guide scope is aligned with the imaging scope (and hence the mount)? http://stargazerslounge.com/topic/217417-aligning-the-finder-to-the-scope-axisimportant-or-not/

You could try switching off DEC guiding and see what happens then.

Does the mount slew normally in appropriate directions using eqmod?

Is your serial mount control cable ok i.e. no damaged, plugged in properly etc.

Can't think of anything else right now!

Louise

[Davey-T]

As Louise suggests, run it with guiding disabled to see which direction it goes in unguided.

Dave

[jimao22]

I'll try to answer to all your questions in order to find out what is happens:

-  am using PHD2, yes

- The mount worked great before, I had an FWHM of 1.9 to some Ha exposures presented here

- last night no trace of error (and no changes to anything mean while)

- the mount behave like this before, occasionally (very rare, that's true)

In my opinion should be soft or electrical problem. Mechanical I don't think we have any connection between both axis to consider this hypotheses.

[Thalestris24]

Hi

Ah, I didn't realise it was an intermittent problem. In that case you'll have to try and do some diagnostics when it occurs.

Good luck!

Louise