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Hi guys.

At the begining of the year I got myself a eq3 pro. The mount was quite stiff on both axes and very hard to balance so I loosened it up a bit to make balancing easier. Since I first tried it I noticed my stars aren't really the right shape when guiding with lacerta mgen so I thought of testing it with phd2. It doesn't even track as it should because I get star trails on 10sec exposures with my ts65 quad, 420mm focal lengh. I don't know much about phd2 because I've been using my lacerta standalone autoguider so far and I just started using and get familiar with phd2. For phd2 Im using a qhy5 on a 9x50 finder-guider.

Last week I setup the mount and got everything ready for a test. I conected the mount and giudecam, calibrated on a star near the meridian and equator, I ran the guiding assistant, applied the recommendations and started guiding. I didn't know if it was good or bad so I asked for a few opinions. I have been told that I might have a problem with the mount and this might be the reason why the graph looks the way it does and the RA is bouncing up and down like that.

This is how the graph looks like20180406_011929.thumb.jpg.3f87c09bd40c003dbbc4c2a6de39a252.jpg

And this is the log for last weeks guiding

PHD2_GuideLog_2018-04-06_000410.txt

I have also been suggested to run the guiding with the guiding output disabled to see the tracking error in the mount and last night I managed to do just that.

The same as last week, I setup the mount, connected everything to phd2, calibrated on a star near the meridian and equator and after that I disabled the guiding output and let it run for about 40min. I think there is definitely a problem with the mout. You can't see it in the photos but the scale was set to 8.

IMG-20180414-WA0045.thumb.jpeg.116763d5867d6ec3c6f9838d3f9a098a.jpegIMG-20180414-WA0048.thumb.jpeg.09ee96f1f544fc8746de38c4dcd9f1f0.jpeg

And this is the guiding log for the ladt night's test with the guiding output disabled.

PHD2_GuideLog_2018-04-14_193919.txt

Could somebody please tell me what the problem might be and how it can be fixed?

I'm thinking of sending the mount to Rother Valley Optics for a full strip and regrease but I would really like to know what the problem might be.

Emil

 

 

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Woah... you say it' stiff in both axis but DEC don' look too bad..hows your balance in RA?

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These peaks are unusual (every aprox. 20 sec). 

(the graph was stretched in PHD2 Log viewer)

As the guide output was disabled on DEC is only the seeing (and RA imperfections) and normal drift (12" in 45 min is a good polar align)

Guide.png

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4 minutes ago, newbie alert said:

Woah... you say it' stiff in both axis but DEC don' look too bad..hows your balance in RA?

I've balanded it as good as I could considering it still is a bit stiff. I have 2 counterweights on the counterweight bar and I'm keeping one in place and the second one is being moved up and down the bar. I put the mount horizontal on the RA axis and slid the counterweight down the bar until the mount started to move. I marked the point on the bar where the the counterweight was when the mount started moving. Then I put the mount horizontal on the RA axis again and pushed the counterweight up the bar until again the mount started to move. Again, I marked the point where the counterweight was when I pushed it up the bar and the mount started to move. I measured the center between thise 2 points and I presume that is the point where the counterweight shoul be to have it balnced.

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4 minutes ago, esrevinU said:

These peaks are unusual (every aprox. 20 sec). 

(the graph was stretched in PHD2 Log viewer)

As the guide output was disabled on DEC is only the seeing (and RA imperfections) and normal drift (12" in 45 min is a good polar align)

Guide.png

I polaralign with a polemaster and redo it again with sharpcap.

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Your situation is very much like mine was with my AVX mount... you have an obvious periodic error every 20 seconds or so which is likely to be caused by an off-centre motor pinion or some other gear.

Two possible solutions... one is to lower the PHD2 camera exposure time from 2 secs down to 0.5 sec... this means PHD2 will correct more frequently and keep the periodic error in check.

Otherwise you can have a go at replacing the motor pinion... see my thread on this: 

 

Also worth mentioning is your guiding kit is identical to mine... a 162mm GS with a QHY5 camera with 5.2um pixels which gives a very low resolution of 6.6"/px which is not ideal. Either a GS with a longer FL and/or a camera with smaller (e.g. 3um) pixels will increase the resolution.

But it's the wobbly RA error that needs attention first.

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4 minutes ago, ChrisEll said:

Your situation is very much like mine was with my AVX mount... you have an obvious periodic error every 20 seconds or so which is likely to be caused by an off-centre motor pinion or some other gear.

Two possible solutions... one is to lower the PHD2 camera exposure time from 2 secs down to 0.5 sec... this means PHD2 will correct more frequently and keep the periodic error in check.

Otherwise you can have a go at replacing the motor pinion... see my thread on this: 

 

Also worth mentioning is your guiding kit is identical to mine... a 162mm GS with a QHY5 camera with 5.2um pixels which gives a very low resolution of 6.6"/px which is not ideal. Either a GS with a longer FL and/or a camera with smaller (e.g. 3um) pixels will increase the resolution.

But it's the wobbly RA error that needs attention first.

I wonder if the RA and DEC motors are the same so I can change them with one aother.

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1 minute ago, emyliano2000 said:

I wonder if the RA and DEC motors are the same so I can change them with one aother.

That would be an easy thing to try first. Try spinning the motors with the gearboxes off to see if it's the culprit.

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2 minutes ago, ChrisEll said:

 

I would never be able to do what you did there.

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3 minutes ago, emyliano2000 said:

I would never be able to do what you did there.

Well, I would take it step by step and try to identify the problem first. Assuming your mount is out of warranty there are lots of guides to help to open up your mount and take a look.

Otherwise try lowering the exp time in PHD2 and see if that helps.

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My EQ3 pro synscan had exactly the same 19-20second periodic error.   The only way I found to flatten it out was to use 0.5s guide exposures.  I also found that a little bit of polar mis-alignment helped the Dec guiding by forcing a little drift and so allowing uni-directional guiding in Dec.  On the scatter graph, PHD2 could then get most hits inside the 2" circle and a decent concentration in the 1" circle.

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14 minutes ago, mikey2000 said:

I also found that a little bit of polar mis-alignment helped the Dec guiding by forcing a little drift and so allowing uni-directional guiding in Dec. 

Yes, this is the way to go with budget GOTO mounts. Don't spend time fretting over Dec backlash, just guide in one direction.

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This is supposed to be my portable mount and I'm planing to use it with my lacerta standalone autoguider so I'm not gonna be using a laptop. Lacerta is different than phd2 and I need to sort out the problem because I don't know if what I'm doing in phd2 to sort out the problem can apply to the lacerta mgen.

Lacerta uses a Sony ICX279AL-E sensor with the following specs:

Screenshot_20180415-152117.thumb.png.84ac115cbc9bc46580453bd68aa9e482.png

and the qhy5 specifications are as follows:

Screenshot_20180415-151859.thumb.png.1110de381e23c7304f18d4a296d55998.png

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Posted (edited)

Would it pe a solution to PEC train the mount in the synscan (V4) for the time when the mount is fully portable (out in the field) and in eqmod for the time when I'm using it at home? If so, should the PEC training  be made while guiding?

Edited by emyliano2000

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Some interesting info here, and yes, I think pec training would be helpful.

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23 minutes ago, knobby said:

 

Some interesting info here, and yes, I think pec training would be helpful.

Considering the mount will never be in the same position, would the PEC training have to be done before each session?

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17 hours ago, emyliano2000 said:

This is supposed to be my portable mount and I'm planing to use it with my lacerta standalone autoguider so I'm not gonna be using a laptop. Lacerta is different than phd2 and I need to sort out the problem because I don't know if what I'm doing in phd2 to sort out the problem can apply to the lacerta mgen.

The Lacerta looks an interesting device and the sales blurb does say "Refresh rate and shutter speed (independently adjustable between 0.1 and 4 sec manually or automatically)" so it looks you may be able to tame the RA error with this device. You can d/l the manuals so you can check.

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17 hours ago, emyliano2000 said:

Would it pe a solution to PEC train the mount in the synscan (V4) for the time when the mount is fully portable (out in the field) and in eqmod for the time when I'm using it at home? If so, should the PEC training  be made while guiding?

PEC won't remove the high frequency PE you have.

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Posted (edited)

it could be that you're too well balanced, so that it's rocking in the backlash on the RA axis ?

Try deliberately unbalancing it by moving the weights so that it's east-heavy - that way the RA motor will always be pushing and maybe will eliminate your rocking.

Dec guiding error of 0.56" is very good, suggesting your polar align is good as well.  In that case, no need to only guide the Dec on one axis (I live in fear that if I do that, then PHD will never get the guidestar back after a dither in the wrong direction).

Edited by glowingturnip

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4 hours ago, glowingturnip said:

it could be that you're too well balanced, so that it's rocking in the backlash on the RA axis ?

Try deliberately unbalancing it by moving the weights so that it's east-heavy - that way the RA motor will always be pushing and maybe will eliminate your rocking.

Dec guiding error of 0.56" is very good, suggesting your polar align is good as well.  In that case, no need to only guide the Dec on one axis (I live in fear that if I do that, then PHD will never get the guidestar back after a dither in the wrong direction).

I did have it east heavy in the first test session but didn't do it in the second one when I disabled the guiding output.

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Posted (edited)

I had a look at the RA motor and it looks fine, I tweaked it a bit, adjusted the backlash again and happy days. All is fine. I was guiding last night with 1.6" RMS error.

Happy days!!!

Edited by emyliano2000
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