Guiding problem

[deanok]

Hi all, ok so this is probably another one of those ‘im having problems guiding’ threads but this one is somewhat strange and must have a very simple answer, it’s just that I’m missing it. I’m hoping someone has encountered the same issue. Let me set the scene.....

I have an eq6 Mount that I bought second hand over a year ago that has has the dark frame belt mod. I run it with apt and PHD2 via eqmod and ascom. I have two scopes on there, an Altair Astro 110mm and Altair 70 mm both with canon eos’... for guiding I have an Altair 50 mm guide scope with a qhy5ll camera. All this has been running sweet as a nut for the last 12 months, literally point, platesolve, choose an object, guide and away..... all evening, every time no issue.

however

over the last week or so it has developed the obsession that every now and then when guiding the ra axis decides to drop like a stone off the graph. PHD2 does bring it back and it continues to guide happily again until it decides to do it again, every 10-15 mins at the moment. Although phd never looses the star ....It is driving me crazy trying to figure out the problem as every second exposure is ruined because  of it.

firstly I checked the usual suspects, balance, cable snags, loose hardware etc etc. No change

then thought it may be a belt/mount issue so I pinged the phd log to dark frame who ensured me that the time scale between ra throwing a wobbly isn’t because of the drive train as the timing doesn’t match.

i have tried the guiding assistant in PHD2 to seei if it has any suggestions and applied the recommendations but still same problem.

 

it is driving me insane ......

 

I will post the phd log for this evening tomorrow ( it is midnight as I type this and to be honest I’ve fallen out with the observatory so best to tackle it in the morning )

any ideas or advice would be very gratefully received 

many thanks

 

Dean

Edited April 19, 2020 by deanok

[MarkAR]

Could it be a clutch slipping?

[deanok]

1 minute ago, MarkAR said:

Could it be a clutch slipping?

Thanks for reply, I have tried locking them as tight as possible and at different pressures ( if you get what I mean ) all the way from literally as tight as poss to almost not on at all . A friend of mine suggested this early on so it was one of the first things I tested .... sadly no difference 

[deanok]

PHD2_DebugLog_2020-04-19_163820.txt

PHD2_GuideLog_2020-04-19_163820.txt

[deanok]

As promised here are a couple of guide logs from last evening..... and a picture of guide graph with ra problem obvious ..

[almcl]

Must start this with a non-expert disclaimer, but a look at your guide and debug logs shows that approximately every 816 seconds your mount stops moving in RA.

Here's a trace of your 34 minute session with the the guiding corrections removed:

and here's the frequency analysis:

Looking at the 109" excursion event at 22.58.53, PHD2 issues 3 maximum length corrections over a 9 second period before the mount starts to move west again.

I think you have a mechanical problem of some sort there in the drive train of the RA axis but not sure what it might be. There's also the possibility that the sidereal rate in the mount is wrong, but I am way beyond my knowledge level at this point.  I am not sure if the gurus at PHD2 site could help as this is clearly not a PHD2 problem, but it might be worth uploading the guide and debug logs (using PHD2's inbuilt uploader) to see if they can suggest a cause/cure?

 

[deanok]

Many thanks for your reply you explained it extremely well.

i have been in contact with dark frame today and decided to send the mount to them for a check up and rectify if needed .... 

I will post what they find on this thread when I know more

 

many thanks

[newbie alert]

What was your guiding looking like before it started to play up, as that looks quite erratic.. Are you well balanced have you run the guiding assistant? It looks like you're over correcting ( giving the see-saw effect) but I see you're doing 3 sec loops.. is there any play in the RA axis? 

[deanok]

The guiding was running smooth as silk last week no matter where I pointed it then the ra problem started so I started to play about with settings.... then ran the assistant and applied the suggested changes and it never really  got better after that... I am convinced it’s a mechanical problem now so it’s being shipped off tomorrow, I’ll post the results when I know more.

[Starflyer]

My guess would be a loose grub screw on either the motor or worm pulley. The pulleys have two grub screws, one tightens against a flat, if there's any looseness the pulley rocks against this flat and gives the symptoms you're seeing.

These shouldn't work loose themselves if tightened correctly when originally assembled or 'tuned'.

 

 

[deanok]

Ok so got my mount back from dark frame optics yesterday ..... after three months !!!! 
apparantly it’s had the full works and is spot on now ..... but I’ve read a bit about them since sending my mount and I’ve got my fingers seriously crossed in hope.

awaiting next clear night so I can polar align and run some guide tests.... watch this space.

[blinky]

have you looked for timeout errors in EQmod?  im having a similar issue, when looking in EQMod i can see it complaining of timeouts

[deanok]

7 minutes ago, blinky said:

have you looked for timeout errors in EQmod?  im having a similar issue, when looking in EQMod i can see it complaining of timeouts

No, not even considered that yet.... hoping to get it back up and running in next few nights to check if the problem has been fixed, if not I’ll be fuming..... and back at square one

[deanok]

Ok so just as closure to this thread..... I got mount back up and running again and it’s guiding perfectly now, no issues.

was a knackered/worn  bearing apparently.

dark frame did a great job, the mount is smoother than ever...... it did however take three months And I didn’t get the photos or test results documentation I was promised... I did get 12 months guarantee, but to be perfectly honest I’m just glad to have it back in working order with no issues so hat off to dark frame for that.

[newbie alert]

14 hours ago, deanok said:

Ok so just as closure to this thread..... I got mount back up and running again and it’s guiding perfectly now, no issues.

was a knackered/worn  bearing apparently.

dark frame did a great job, the mount is smoother than ever...... it did however take three months And I didn’t get the photos or test results documentation I was promised... I did get 12 months guarantee, but to be perfectly honest I’m just glad to have it back in working order with no issues so hat off to dark frame for that.

The worm bearings should of been changed on its tune up, bear in mind what we ask if from a mount speed point of view is nothing like what the spec of the bearing is rated at..