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Andyb90

PHD2 Guiding - Very Spikey Graph - Help!

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1 hour ago, Uranium235 said:

No prob, I've just cobbled together the required files in anticipation. What camera is it? (QHY5?)

Qhy5II

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Hi Andy

I'd run without guiding and see how things behave. Make sure there is no flex especially between the guide scope and the imaging scope.

Louise

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Yes I'll check with guiding turned off and run the guiding assistant for longer too.

Also here is a picture of how my 9 x 50 finder guider is attached to the tube rings my 80 ED sits in.

I'm wondering if its solid enough to avoid flex or if there is something I should change.

I thread the cables from the QHY5 through the 2 pieces of elastic that are on the top dovetail bar to try and keep them from moving or dragging.

56c8f6b26f256_finderguidescope.thumb.jpg

Andy.

Edited by Andyb90

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That should be fine. Just wondering what focal length you entered for the guide scope in PHD2? It uses that to calculate the arc secs in the graph. How are stars coming out in images?

 

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I entered the focal length as 180mm, but just read this thread where it also mentions 162mm.

To be honest I spent the whole session trying to work out what was happening with the graph, so I didn't take any test subs. I assumed I'd got no chance with the graph being so spikey.

I'll ensure to do a few subs next session though, even if I can't get any improvement in the graph.

 

Andy.

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I just had a look at your log file.

The first thing that struck me is that your HFD on the calibration run was 4.37px at a scale of 6.42 arcsec/px. Otherwise it looks like a good calibration. I'm no expert on what is a good HFD but 28 arcsec for a guide star sounds big.

And on the final run HFD was 2.67 px which is better but still over 17 arc-seconds.

I ignored the middle runs as there were too many alterations being made to the settings.

The second observation is that you didn't input a declination for the cal run. Not a problem if the guide runs are at roughly the same declination. But also, the calibration has the RA rate roughly half the Dec rate which suggest you calibrated halfway or thereabouts to the celestial equator. But PHD thinks you were at the equator. If you then start guiding near the equator, PHD will not give enough RA correction.

The third observation is that there is no drift alignment run so we don't know how good your PA is.The problem at 21:26 looks like backlash being cleared before the mount responded.

Unfortunately it doesn't go much after that to see if things got better with the backlash cleared

The big RA spike at 21:10 came when you were changing settings so may be nothing. 

For now I'd say turn on the star profile display View > Display Star Profile and see how it looks next time. Post a screen shot of the star profile you use.

Also, enter Dec when you calibrate. 

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48 minutes ago, Andyb90 said:

I entered the focal length as 180mm, but just read this thread where it also mentions 162mm.

To be honest I spent the whole session trying to work out what was happening with the graph, so I didn't take any test subs. I assumed I'd got no chance with the graph being so spikey.

I'll ensure to do a few subs next session though, even if I can't get any improvement in the graph.

 

Andy.

I put 170mm for mine - the approx. measured distance from the objective plane to the sensor plane but 180 shouldn't cause any excessive mismatch for the graph. +1 for displaying the star profile. One source of problems with the heq5 can be the collar around the counterweight bar which can be too tight and sticky. I tried ST4 guiding with a qhy5l-ii and a Star Adventurer but it didn't seem to work very well at all. Then I realised that the ST4 port was disabled because I had the camera set to 12-bit mode. Didn't get any warnings...

 

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I see your post on the PHD forum, Bruce is very knowledgable, he has given you some good suggestions, I hope they help to solve your guiding problems.

Ray

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Yes it was a very informative response. Not good news, but at least I have an idea what I'm up against.

Here is the link to my open PHD post for anyone who may have similar issues:

https://groups.google.com/forum/m/#!topic/open-phd-guiding/4Vwuzbn8reo

I'll make the suggested changes for PHD2, test guiding Dec etc to see if I can get any slight improvement. I guess this will be little at best.

I'll post a separate thread in the mount discussion section for help on the specific mechanical issues as I'm not sure exactly what action to take. I'll do some research.

Must say I'm a bit disappointed it appears my HEQ5 is unguidable. The mount is only 6 months old. I thought about tuning and possibly the belt mod when the mount was older but wasn't expecting to need it now. Maybe my expectations were too high.

Andy.

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12 hours ago, Andyb90 said:

 

 Hi Andy

Are you sure you're guiding at all? I think it unlikely it's a mount problem - more likely an ST4/ST4 cable problem. Can you setup pulse guiding - it's better in a number of respects and will, at least, allow you to check things out

Louise

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I think commands were getting to the mount judging by the noise it was making, but I can setup pulse guiding as I have EQ ASCOM on my laptop and an EQ Direct cable.

Will give it a go.

I was wondering whether there might be some kind of vibration making the guide star appear to move. Although I can't think what it might be. I don't stay near the mount as I control things from a tablet in the house. Will double check to ensure all connections and screws are tight.

Andy.

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I guess lots of things can make a guide star appear to move - flex, atmosphere, clouds, thermals, cables pulling etc. If it comes to it you could maybe run the heq5 with just the guide scope on it.

Louise

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I've also got an st80 which I could try as a guide scope again . I went for the finder guider for reduced weight, but I'd still be within the mounts capacity using the st80.

This time though I'll be more patient making changes and make them in smaller increments. I think I got a bit carried away in PHD and tried to make alterations too quickly.

Andy.

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I wouldn't change anything mechanical just yet as it will just cloud the waters. You need to go back to scratch and get the basics right first. 

  • Reset PHD2 to its default settings
  • Connect your camera and mount
  • Slew to a bright star near the celestial equator and near the meridian - either just west of it or not too close on the east. You don't want a meridian flip while you sort things out.
  • Check the star display and make sure the star is in focus and not saturated (flat top profile). Take a screen shot of the profile.
  • Do a calibration run. If you don't have comms between PHD2 and the mount, enter the declination within a few degrees.
  • Check the calibration.
  • If the calibration is good, turn off guiding pulses and do an unguided run for about 30 minutes on the same star to get 3 cycles of the worm drive. This will show you several things: how good your polar alignment is, how much periodic error you have, any other mechanical issues.

You need the data to troubleshoot your problems.

 

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I been looking at this post trying to get my head round it. I still useing a Heq5 as it come out the box and not done any thing to it in over five years and I runing 12.5 kg and still run

PHD up to 20 mins each subs on a good night ,  its good to see you geting lost of help and hope you find out why its not work well. Sorry That I can help as I do not know how to put it right. you can try next time out by just pushing on bits just to see if everything is lock down .

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Will go back to basics as suggested. Tomorrow night looks like it will be clear for me so I will do some more testing then and post the results.

Also I was thinking should the QHY5 guide camera by orientated (rotated) in a particular way or does this not matter?

Andy.

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If your orientation is set in a way that your calibration shows your movement in north, as north and your calibration shows east as east.

and you angle of rotation is either zero or 180degs or close enough. Then it makes it easier to diagnose what's going on, other than that it makes no difference. I can't remember if the qhy5 has a square sensor or not, my qhy 5-Lii is oblong.

Ray

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The sky was clear last night :icon_biggrin: so I was able  to do some more testing. I reset the PHD settings and calibrated on a star near the meridian and DEC zero. Here is the start profile:

Capturestar23.JPG.381666ed7789cf9dc40c68

And the calibration results:

Capture23cal.JPG.7b8113e519da890cef3a4cf

I've also attached the PHD2 guide log with 30 minutes of guiding disabled (section 6) of the log.

PHD2_GuideLog_2016-02-23_222842.txt

Both RA and DEC seem to be very spikey.

Andy.

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That's a much better star profile and a fair calibration. The drift to the east on the decllination leg is a bit of a worry, maybe its a bit of backlash that wasn't cleared. Others may have a better idea.

The guide log shows the periodic error on the blue line and it looks to be about 40" p-p which is on the high side. Checking it out in PecPrep the offending frequency is 380 seconds which is caused by the transfer gear. You could try improving the meshing of that gear.

You have 50" of declination drift in half an hour - my back of envelope calculation says your Polar alignment error is around 6.3 arc-minutes which is more than you'd want for imaging. We tend to aim for 1 arc-minute. You probably need to drift align.

Since you aren't guiding, the spikiness (the high frequency stuff - not the periodic error) is down to seeing and vibrations. It looks pretty normal to me. If I put in a high pass filter in PecPrep its around 1 arc-second RMS. Not that you can do anything about it

 

 

Edited by kens

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Thanks for the feedback. Is the transfer gear the worm gear or are they different?

I've looked at a guide for adjusting the RA worm engagement.

I've also seen there is a belt drive modification for the HEQ5 mount. Could that help to improve backlash?

Andy.

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I've taken the motor cover off the mount and had a look at the gears.

I can rock the RA worm gear back and forth slightly within the teeth of the connecting  gear (idle gear I think). It is only a slight movement though.

The Dec worm gear is looser. I can easily rock it back and forth within the teeth of the connecting gear.

Is the purpose of the worm adjustment to reduce this play? Does it move the worm gear closer to the connecting (idle) gear?

Also I can see the teeth of the gears are quiet grimey. I did a quick dab with a cotton bud and it's grey in colour. So I'm assuming it would be a good idea to give them a clean and re-grease.

Andy.

 

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11 minutes ago, Andyb90 said:

I've taken the motor cover off the mount and had a look at the gears.

I can rock the RA worm gear back and forth slightly within the teeth of the connecting  gear (idle gear I think). It is only a slight movement though.

The Dec worm gear is looser. I can easily rock it back and forth within the teeth of the connecting gear.

Is the purpose of the worm adjustment to reduce this play? Does it move the worm gear closer to the connecting (idle) gear?

Also I can see the teeth of the gears are quiet grimey. I did a quick dab with a cotton bud and it's grey in colour. So I'm assuming it would be a good idea to give them a clean and re-grease.

Andy.

 

Hi

That's just the motor gear - which can be adjusted or replaced with a belt mod. For the worm gear it's best to follow Astrobaby's guide step by step.

Louise

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The transfer gear is the idler that comes between the motor gear and the worm.  This is where most of your periodic error is coming from and unfortunately cannot be cancelled with periodic Error Correction although it can be guided out. But it would be good to reduce it as much as you can along with any other "looseness".

To be pedantic, the worm is the screw shaped gear and the worm gear (or worm wheel) is the gear that is driven by the worm.

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I've ordered the Rowan belt kit, so that should be with me very soon.

I think I misunderstood the worm engagement adjustment, but having seen more images of the dec axis I now understand what you mean by the worm wheel and worm.

I also just read an article on an EQ6 tune up which highlights the below advantage for the belt drive. I hadn't considered it before but it sounds good.

"The best thing about the belt conversion is that you can now adjust worm to ring engagement without creating binding in your motor pinion/transfer gear train and tension the belt without affecting worm engagement."

Also I've read other posts where the following has been done to improve guiding:

  • Replacement of bearings
  • Upgrade of saddle
  • Upgrade of tripod

Any opinions or experience for the above 3 options would be appreciated.

Andy.

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