My DEC is running away from me

[Obi Wan Ken00bi]

Hi SGL!

Can you help me solve this mystery? After 45 minutes of ok guiding within 1,5 archseconds, the DEC kept running away. I tried:

• reconnecting the cables 
• restarted PHD 2.0 software
• changed some of the Dec related settings like aggresiveness and max duration in PHD
• realigned the mount (started from scratch) and realigned the target
• changed the balancing on the scope

But the problem kept occuring. Do any of you recognise this strange behaviour?

 

Also a video here:

 

Can you help?

[newbie alert]

Clutches done up tight?

[Thalestris24]

You didn't mention PA? Either your PA is off or you're unbalanced - Have you balanced your scope in RA, DEC and vertically? What happens when you run unguided e.g. using the guiding assistant?

Louise

[Obi Wan Ken00bi]

1 hour ago, newbie alert said:

Clutches done up tight?

Good question. I believe so, but I will check next time out! 

[Obi Wan Ken00bi]

1 hour ago, Thalestris24 said:

You didn't mention PA? Either your PA is off or you're unbalanced - Have you balanced your scope in RA, DEC and vertically? What happens when you run unguided e.g. using the guiding assistant?

Louise

What is balancing vertically? Is this placing the tube vertically and seeing if it falls downward to a side? 

Also I've never run guiding assistant.... so much to learn! I presume here you can chdck your unguided performance? 

 

 

[spillage]

Looks like a PA issues as your DEC is showing nearly 4" error.

[Obi Wan Ken00bi]

PA was fairly good I believe, but I could have had it very wrong (like even the wrong star in there)

I did manage to grab my first Veil nebula image before things went haywire, but PHD was working overtime.

 

Thanks for the tips so far

[spillage]

How do you setup your PA?

[Thalestris24]

27 minutes ago, Obi Wan Ken00bi said:

What is balancing vertically? Is this placing the tube vertically and seeing if it falls downward to a side? 

Also I've never run guiding assistant.... so much to learn! I presume here you can chdck your unguided performance? 

 

 

Yeah. I was thinking - had you maybe just done a meridian flip?

[Davey-T]

Looks like the mount is ignoring the PHD corrections.

May be excessive backlash.

To see if it's balance or slipping clutch try gently helping it in the right direction with your hand, one finger should do.

Dave

[michael8554]

1. Why is Dec heading off so quickly ? Is your PA that bad? You could run Guiding Assistant before imaging, this will report your PA, as well as best settings for that night's seeing.

2. PHD2 is issuing longer and longer corrections but the mount isn't moving. This could be the mount trying to overcome stiction, but I think if it was that the last big correction would have unstuck the dec and sent the mount hurtling over to the other side of the axis. Instead it goes nicely back to the axis. So PHD2 is just taking up backlash that has become apparent in that scope orientation. Then the poor PA immediately sends Dec off on a trip again. Loose Az adjustment?

Michael 

[Obi Wan Ken00bi]

12 hours ago, Thalestris24 said:

Yeah. I was thinking - had you maybe just done a meridian flip?

That's the funny thing, the mount was going over it's meridian, so after I saw this behavior, I resend the mount to the target and it did do a meridian flip. The issue persisted though.

[Obi Wan Ken00bi]

10 hours ago, michael8554 said:

1. Why is Dec heading off so quickly ? Is your PA that bad? You could run Guiding Assistant before imaging, this will report your PA, as well as best settings for that night's seeing.

2. PHD2 is issuing longer and longer corrections but the mount isn't moving. This could be the mount trying to overcome stiction, but I think if it was that the last big correction would have unstuck the dec and sent the mount hurtling over to the other side of the axis. Instead it goes nicely back to the axis. So PHD2 is just taking up backlash that has become apparent in that scope orientation. Then the poor PA immediately sends Dec off on a trip again. Loose Az adjustment?

Michael 

My PA was pretty good I think (I use the build in Polar scope on the EQ6). Thank you all for all the tips. 

To sum up, next time I will:

• Make sure the scope is balanced not just in RA and Dec, but also vertically
• Make sure the adjustment levers on the RA and Dec are tightened rock solid
• Make sure a proper PA is achieved and:
• Run Guiding Assitant before guiding to check PA and the balance of the whole setup

Shout if I miss anything

[spillage]

I would only use the polar scope that comes with the mount for a rough polar alignment.  Either use phd to sort our your PA (finish it with the drift align routine) or give sharpcap a go. I think sharpcap is £10 a year and has a polar alignment routine that is similar to the qhy polemaster.

[Anthonyexmouth]

+1 for sharpcap. Polar scope gets you in the right area for visual/goto use but not a patch on sharpcap or drift alignment for AP

[Thalestris24]

1 hour ago, Obi Wan Ken00bi said:

That's the funny thing, the mount was going over it's meridian, so after I saw this behavior, I resend the mount to the target and it did do a meridian flip. The issue persisted though.

I think you have to be careful and aware of what's going on near the Meridian. I have to say I've never done a Meridian flip whilst imaging as I'm constrained to only image to the East. However, there are Meridian DEC settings in PHD2 to be aware of and also mount limit settings in Eqmod. I'll leave you to research those for yourself. You can just Google them

Louise

[Shibby]

On 15/08/2018 at 10:35, Obi Wan Ken00bi said:

Shout if I miss anything

Definitely try clearing your calibration data in PHD after you've set up.

Also, check you haven't accidentally reduced your mount's guide rate - it looks like the commands can't keep up with the alignment error or aren't getting through at all.

[Obi Wan Ken00bi]

1 hour ago, Shibby said:

Definitely try clearing your calibration data in PHD after you've set up.

Also, check you haven't accidentally reduced your mount's guide rate - it looks like the commands can't keep up with the alignment error or aren't getting through at all.

How would one reduce the mounts guide rate? (Is that in the Synscan controller itself? I don't think I've changed things there......)

[Obi Wan Ken00bi]

Thanks for all your tips and tricks. I’ve implemented the changes, although SharpCap couldn’t resolve the polar field (need a smaller guidescope I think). This guidecurve is way better  

[Davey-T]

Looking a lot better now, a bit more fettling and you can probably get the outlying target hits closer to the centre of the bulls eye.

Dave

[Obi Wan Ken00bi]

So the weird thing is, after the meridian flip it did the same thing again! Even after restarting PHD2 and clearing calibration data. I ended up just imaging on the western side of meridian and preventing the flip. My PA was spot in.

Next time I’ll just image in one side or disable dec guiding

 

anyway, I still managed to get these shots  

[Davey-T]

Looks like the dec pulses aren't getting through or they can't override the backlash.

Did you try giving it a helping hand to override any backlash ?

Dave

[Thalestris24]

3" isn't much! Does it settle down in time? If it does, it's probably just backlash. FWIW my guiding is only ever around +/-4" at best. Did you adjust the eqmod/phd2 dec settings as I mentioned previously? Other than that, it could be a balance issue or cone error

Louise

[Obi Wan Ken00bi]

5 hours ago, Davey-T said:

Looks like the dec pulses aren't getting through or they can't override the backlash.

Did you try giving it a helping hand to override any backlash ?

Dave

No I didn’t do that. Will try next time. I just got a bit frustrated and went back to the other side of the meridian haha. 

Louise: I deleted the calibration data after the flip so I don’t ticking the reverse meridian box makes sense? I won’t delete the calibration data next time and change the PhD settings. I’m not using EQMod (yet). 

 

Ill try the last tricks (cone error video is interesting btw!) and report back on the next clear sky!

[Thalestris24]

phd2 after meridian flip

eqmod and mount limits 

Louise