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My RA axis stopped working last night

Sky-Watcher HEQ5 PRO Open PHD Guiding Project PHD2 Equatorial Mount Guiding Troubleshooting
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Andy Wray avatar
Andy Wray avatar
Just in case this happens to anyone else:

For a long time my guiding in the RA axis has been a bit iffy and I was getting regular corrections in both directions. 

Last night even my tracking started to fail in the RA axis.  Also, my gotos seemed to be missing the mark by quite a bit.

I was up until 3am trying to troubleshoot it as follows:

* Tried PHD2 guiding assistant in multiple parts of the sky
* Cleared the ASCOM sync points and re-platesolved around the sky
* Re-did the RA axis backlash (not so easy in the dark)
* Re-balanced the scope
* Multiple re-starts and working with the handset to see what was/wasn't working
* Tightened everything up (clutches, tripod etc.)
* Adjusted worm gear end floats

Nothing worked!  I actually thought I'd somehow stripped the gears on my RA axis.

In the end it turned out that one of the grub screws on one of the RA axis belt drive gears had worked loose.  Obvious in hindsight.  It should have been obvious to me as the motors were wherring merrily and happily away (i.e. no crunching, gear binding sounds) and yet the scope was going nowwhere.
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siberx avatar
siberx avatar
Might be a good idea to add some loctite to the grub screw so it doesn't back out in the future.
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Andy Wray avatar
Andy Wray avatar
Might be a good idea to add some loctite to the grub screw so it doesn't back out in the future.

Not a bad idea.  When I opened the cover to the gears it was just sitting there (had worked all the way out) saying to me "look at me, aren't I clever?  I am the culprit".
Michael Cullen avatar
Michael Cullen avatar
Mine did the same thing.  I ended up getting the Rowan belt mod and it's been working great ever since.
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Andy Wray avatar
Andy Wray avatar
Michael Cullen:
Mine did the same thing.  I ended up getting the Rowan belt mod and it's been working great ever since.

I have the Rowan belt mod.  I clearly didn't tighten the grub screws quite enough when I did the mod and it's been slowly working loose over the past year without me knowing.  I guess I'd assumed that because I was getting sub-0.7 arc secs guiding everything was fine in there.  Let's hope this fixes some of the weird star shapes I've been seeing recently.
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Gary JONES avatar
Gary JONES avatar
I had the Rowan belt mod installed yesterday - keen to try it out when the weather clears.

Michael and Andy - how much improved was your tracking after installing the mod ?

Gary
Linus avatar
Linus avatar
Haha, this brings me back. Exactly the same thing happened to me and I was pulling my hairs out until I realized that the rowan belt kit doesn't perfectly line up with the motor drive shaft and I hadn't tightened the grubscrew on the "flat" area. Funny how such a small thing can make you feel so stupid.
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Andy Wray avatar
Andy Wray avatar
Gary JONES:
I had the Rowan belt mod installed yesterday - keen to try it out when the weather clears.

Michael and Andy - how much improved was your tracking after installing the mod ?

Gary

If I'm honest, the Rowan belt mod didn't really improve my tracking that much when I was using a separate guide scope.  The thing I noticed most of all was how quiet and smooth the mount was afterwards.  The thing that really improved my tracking (from about 1.5 arc secs to about 0.7 arc secs) was moving to an OAG.
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Andy Wray avatar
Andy Wray avatar
FWIW:  this is probably the moment last night when my RA grub screw eventually decided it had had enough.  I'll post later what I'm hoping will be a much better guiding graph (sub 0.5 arc secs?):


[Update] Having fixed the grub screw and had a couple of hours tonight guiding, the results are that: my best guiding has been 0.4 arc secs RMS and my worst 0.55 arc secs RMS.  This is not too shabby for an HEQ 5 Pro in a Bortle 5 zone    I'm actually quite glad it failed last night.

Here is just one 5 minute Ha Sub (no flats or darks applied) of the bubble nebula with the new guiding (I can't wait until I get a full SHO image of this):
Gary JONES avatar
Gary JONES avatar
Hi Andy,
Thanks for your quick reply …

Yes, it's certainly much nicer to have a quiet mount rather than one that makes that horrible grinding sound - not surprising really when you look at the size of the gears and the manufacturing quality.

Interesting to capture the moment when the grub screw fell out smile

Clear skies,

Gary
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Andy Wray avatar
Andy Wray avatar
and here is a typical guiding session from tonight with the grub screw back in place   Very happy with it considering I am on the limits of the mount's payload capacity.  0.45 arc secs RMS guiding is just right for my image scale of 0.865 arc secs per pixel.
Gary JONES avatar
Gary JONES avatar
Hi Andy,
That  guiding looks great - particularly with Aggr set to 100% ... I certainly wouldn't complain about that result on my system

Out of the box I got 2-3" using a ASIAir Pro (which I understand uses PHD internally), before the Rowan mod and with no adjustments. Aggr is probably too high, I'm sure I can get a better result with some fine-tuning.


Now I've done the Rowan mod, I'll do another session when the weather clears and post my results
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