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Posted (edited)

Hi All, wondered if you could help me make sense of this ... new HEQ5 - belt modded by FLO, all feels good, minuscule backlash but strange guiding.

Admittedly first time using it but baffled.

Failed calibration see image below and guiding seemed to be Ra and Dec following each other.

Stars look ok ish (@ 1500 mm )

Needle galaxy is poor as only about 10 mins each in RGB

note - it was hazy and did keep losing star in OAG

 

Thanks for looking

PHD2_DebugLog_2020-05-19_221608.txt

 

image.png.8067a6c54eddd2b05236aedce662d008.png

image.thumb.png.4bf14acd8906515ff27ddd4fb2477fd2.png

PSX_20200520_110421.jpg

Edited by knobby

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From the phd site

Orthogonality error - the camera axes are normally computed independently even though they should be perpendicular.  The angle calculations do not require great precision, but if they are signfiicantly non-orthogonal, you should repeat the calibration.  If you see repetitive alerts of this type and the axes are significantly non-orthogonal, you'll need to identify the problem and fix it.  Common causes are bad polar alignment, large declination backlash, or large periodic error in RA.  Any of these problems can cause the guide star to move significantly on one axis while PHD2 is trying to measure its motion on the other axis. If you suspect these problems, go ahead and accept the calibration, then run the Guiding Assistant to measure your polar alignment error, declination backlash, and RA tracking error.  In other cases, the mount may not be moving at all, and the measured displacements of the star are just caused by seeing effects.  This sort of problem should be obvious in the calibration graph at the left of the dialog.  If the axis error is relatively small and you are convinced the hardware is working properly, you can avoid further alerts of this type by setting the option to 'Assume Dec orthogonal to RA' in the 'Guiding' tab of the Advanced Setup dialog. But you should do this only if the error is fairly small - otherwise, you are simply ignoring a serious problem.  

https://openphdguiding.org/man-dev/Trouble_shooting.htm

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Thanks @wimvb I guess I'll have to have a dabble again next clear night. Just weird though.

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Hi knobby

You've posted the Debug Log, please post the Guide Log.

But I'd hazard a guess you're ST4 guiding with a faulty cable.

Michael

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Posted (edited)

Thanks knobby

Looks like there's a lot of Dec Backlash - 17 steps, one every 2.5 secs.

This may be all that's causing the poor Calibration.

Before Calibrating, you need to nudge the mount north until you see the star move,  to clear the backlash.

Your PA appears good, so Dec didn't need correcting.

So luckily the RA moves that are being repeated in Dec weren't enough to mess up your guiding too much   🙂

So orient your guidescope so that E-W moves are roughly horizontal across the screen when pointing south at Dec 0.

Then try the  PHD2 Manual Guide in the Tools menu, with a large Step Size, say 5000.

Move west enough button presses to see significant movement - is it only west, or is it moving north or south too ?

Then try North moves, are they vertical moves up or down the screen, or is there east or west movement too ?

If interaction seen, check out your cables, or perhaps try to simplify things by trying ST4 (only as a test, ASCOM is the way to guide)

After you have RA and Dec no longer interacting and have a good Calibration, run the PHD2 Guide Assistant to get the right Minimum Move settings.

It's all in these Best Practices from the PHD2 Developers:

https://openphdguiding.org/phd2-best-practices/

Michael

 

Edited by michael8554
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Thanks Michael, it's a brand new mount, cant feel any backlash (slight on Ra) I'm wondering if the fact that It kept losing the guide star might be the culprit. Another night of explaining to Mrs Knobby that 'no I haven't taken any pictures' just dabbling !

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Perhaps a long duration star loss during Cal could be the cause, PHD2 pauses Cal until the star comes back.

Backlash - we're talking microns of movement here, too small to feel, so if you can feel backlash it's miles out !

Brand new ? Send it back with the guidelogs.

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The backlash I can feel is in Ra though ?

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RA not such a problem as always driving in the same direction but not ideal.

Michael

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Thanks for the help with this, I'm just trying to sus if it's me and my garden (surrounded by houses up to about 45 degrees so fairly poor seeing or a problem with my shiney new belt modded mount. Tried again last night for about 90 mins in total including pa. Mount / scope was pretty much perfectly balanced but very slightly east heavy. Using an OAG / C8 reduced to 1500 mm ,managed to calibrate albeit poorly but the RA guiding was inconsistent and still showing high backlash although dec guiding was very good.

I,m slightly underwhelmed as my £250 Az-Gti guides just as well if not better.

Could it be my location ?

Next step for me will be to try finder guider to discount the OAG as it keeps losing stars even at 3 seconds

Logs attached and thanks again.

PHD2_GuideLog_2020-05-24_215740.txt

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2 hours ago, knobby said:

I'm just trying to sus if it's me and my garden

Where do you set up your mount? If it's on a lawn or other soft surface, put a brick or something underneath each leg of your tripod. I used three fence post anchors in the soil, and left them there. 

https://www.ebay.co.uk/itm/Zinc-Plated-U-Type-Post-Fence-Foot-Anchors-Packs-/262736097733

Mine were L-type, with the vertical part removed. 

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Posted (edited)

Hi knobby

You were guiding on poor Calibrations, you must get Cal right before you think about guiding.

I don't think you followed the instruction to nudge north to clear your large Dec Backlash before Calibrating, so PHD2 did poor Calibrations.

You seem to be in denial over the Dec Backlash ?

I'm only going by the Log results - perhaps FLO should comment ?

You did a Guide Assistant run, but didn't accept the recommendations !!

Minimum Moves and Backlash Comp for instance.

So your PA was good, so Dec wouldn't need much guiding, if any at all.

But you stuck with a tiny Min Move setting, so Dec was continually reacting to every tiny twitch in Seeing.

Same with RA Min you could get RA down to Dec figure if the nount wasn't reacting to every twitch in the star.

Don't even think about a wobbly Finder Guider to guide at 1400mm.

Michael

Edited by michael8554
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Posted (edited)

Thanks again, it was a very rushed session inbetween  clouds, I guess I'm not being fair on the mount but just want to see it guide accurately before I've had it too long for @FLOto be able to accept it back as faulty. I was sure I pressed the accept guide assistant suggestions but clearly too rushed 😅

Edit - set up on concrete paved patio.

Edited by knobby

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Hi Knobby

Remember that with a belt mod you want very good balancing, no East heavy!

Louise

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37 minutes ago, Thalestris24 said:

Hi Knobby

Remember that with a belt mod you want very good balancing, no East heavy!

Louise

Cheers Louise, it was just a teeny weeny bit east heavy as ironically, there is a small amount of backlash in Ra.

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New HEQ5 with belts? You should have an almost perfect L shape on calibration.

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Posted (edited)

So, again thanks to all for input, had another crack last night ... balanced as well as possible in dec and ra, got PA to sub 1 arc min in sharpcap, chose a star near dec 0 to calibrate on and calibration was horrid again. Tried the nudge North suggested by @michael8554 which helped and then passed calibration (badly though) I've run motors round and round for ages incase something was 'bedding in' but still only guides at 1+ in ra and 0.6 ish in dec.

Attached guide logs again and will copy @FLO in by email.

Annoyingly it guides at 0.7 and 0.5 for a few minutes occasionally then has a fit randomly up to 2 ish in ra.

Cables scrunchied to side of mount head, no wind, no dew shield - C8 edge 0.7 reducer and OAG.

Really don't want to send it back 😞 pretty gutted.

edit - forgot to say, ran guide assistant and accepted suggestions.

PHD2_GuideLog_2020-05-25_140529.txt

Edited by knobby
Added info

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Any thoughts on this suggestion ?

I would go back and experiment with varying the min/max moves in PHD.

Try using an RA Duration value of 150 - that equates to a max move of approx 1.25" at a guide rate 0f 0.5x.

Also increase the Calibration step size. I sample at 0.61" and find a value of 450ms gives a good calibration.

At the end of the day I think you need to spend more time experimenting with the guide settings and trying to get a god calibration as imaging at 0.52" requires very accurate guiding if you hope to get round stars.

If you get nowhere then of course you can return the mount but I think it unlikely that you will get good reliable guiding at your plate scale without some experimentation.

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I'd say you're getting there Knobby.

The last run was RA 0.75arcsecs, Dec  0.44arcsecs.

Dec was hardly getting guided at all - good.

RA was overshooting a bit, try reducing RA Aggression until you see RA smoothing out, to get RA down to match Dec .

The need to nudge north before Calibration isn't my idea, it's an essential requirement from the PHD2 Developers.

If you don't do that you won't get a good Cal, and your Cals are still poor.

Cal Step Size is correct, 12 to 13 steps on RA, but I would try upping the Guide Speed even more, to the max, and see how it helps Dec.

You accepted the Guide Assistant Min Moves this time and that made a big difference.

Focus is still poor.

There's been suggestions to get balance spot on with belt drive, but there is still worm backlash to contend with, so that doesn't compute for me.

Almost there.

Michael

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Actually I've changed my mind.

Although the Dec Calibration is awful, because your PA is good, Dec is chugging along just fine with almost no guiding necessary.

So belay the Guide Rate change, but try the RA Aggression changes.

And Focus.

Michael

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22 hours ago, knobby said:

Cheers Louise, it was just a teeny weeny bit east heavy as ironically, there is a small amount of backlash in Ra.

Hi again Knobby

You shouldn't have any backlash with a belt mod - unless the belt tension is maladjusted, or you are out of balance, or have cable drag or similar. Double check that the mount still balances ok vertically. In my experience, even with a small scope the belt mod is sensitive to small amounts of imbalance. You mentioned somewhere above that you keep losing the guide star - is that because the mount is drifting away from it rather than, say, poor sky transparency? The Guiding Assistant should show how your mount+scope is behaving independent of guiding and sky conditions. What figures does it return in respect of RA and DEC behaviour? Are you sure your PA is spot on - you need good PA to get a good calibration, and sometimes you need to do several iterations.

If everything checks out otherwise then the simplest explanation will be the belt tension being off. I did my own belt mod (a few years ago now) and had to make several adjustments before I got it right. It's been excellent since 🙂 

Hope you can sort it - it's so good when it's up and running!

Louise

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32 minutes ago, Thalestris24 said:

Hi again Knobby

You shouldn't have any backlash with a belt mod - unless the belt tension is maladjusted, or you are out of balance, or have cable drag or similar. Double check that the mount still balances ok vertically. In my experience, even with a small scope the belt mod is sensitive to small amounts of imbalance. You mentioned somewhere above that you keep losing the guide star - is that because the mount is drifting away from it rather than, say, poor sky transparency? The Guiding Assistant should show how your mount+scope is behaving independent of guiding and sky conditions. What figures does it return in respect of RA and DEC behaviour? Are you sure your PA is spot on - you need good PA to get a good calibration, and sometimes you need to do several iterations.

If everything checks out otherwise then the simplest explanation will be the belt tension being off. I did my own belt mod (a few years ago now) and had to make several adjustments before I got it right. It's been excellent since 🙂 

Hope you can sort it - it's so good when it's up and running!

Louise

Guide star was poor transparency and movement when calibrating

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3 hours ago, Thalestris24 said:

You shouldn't have any backlash with a belt mod

Hi Louise

I can see that the belt mod removes harmonics due to the spur gears, and runs quieter, but I don't understand how it can remove the fundamental, the worm and worm-gear backlash ?

Michael

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3 minutes ago, michael8554 said:

Hi Louise

I can see that the belt mod removes harmonics due to the spur gears, and runs quieter, but I don't understand how it can remove the fundamental, the worm and worm-gear backlash ?

Michael

Agreed, it still has a worm drive so some backlash will still be there. Quite a lot by the looks of mine 🙂 

But seriously, I'm feeling seriously down about this, looks like another night of piddling around trying to get it to calibrate / guide.

Thanks all for your support.

image.png.b00ad2cf2a51537c437427c648826428.png

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