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RA and DEC runaway


Phillyo

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Good morning all,

For the last few sessions out my guiding has been terrible. Around 3-4" RMS, where previously it had been around 0.7" approx. So, I calibrated last night then ran the guiding assistant. During calibration the orthogonality error was quite high and then during the guiding assistant everything was going ok with a PA error around 3 arc-min, when all of a sudden both RA and DEC just dropped off. I stopped it running as it was never coming back. I checked the mount for any cable snags but nothing was dragging or catching. I was pointing east around maybe 40 degrees? 

I have the logs from PHD2 but they're at home (I'm at work) so I'll upload them later on, but in the mean time I'm just wondering if anyone has any ideas?

The DEC calibration looked really strange too, the logs will show what I mean.

Thanks,

Phil.

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1 hour ago, Peter Drew said:

RA and DEC runaways are often the result of poor contact causing power loss.  The easiest and cheapest solution hopefully is to examine and clean the contacts.    🙂

I assume you mean powerloss to the mount itself? Or to the guider/mini pc controlling the software etc?

Thank you.

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I've taken the connector off and given it a bit of a clean, I've changed a few power leads around too so fingers crossed it'll help. I've also done a quick mount tune up to remove some of the stiction in RA and DEC.

For info, the guide logs including the calibration and the strange graph report are both here: https://openphdguiding.org/logs/dl/PHD2_logs_DyLG.zip

I would ignore the last two guiding logs as I was just messing around there, but you can see from the other log the RA and DEC running away after a minute or so of the guiding assistant.

Phil.

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7 hours ago, Phillyo said:

EQ6R Pro mount.

Your backlash results look good, but your graph on the left looks a bit strange for sure!

You could use the word strange... This was caused by a loose Dec worm housing in a cem 60... It was impossible to guide on one side of the pier would run away with itself.i spent far too long trying to fix the fault within phd, when the issue was a mechanical one

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3 hours ago, newbie alert said:

You could use the word strange... This was caused by a loose Dec worm housing in a cem 60... It was impossible to guide on one side of the pier would run away with itself.i spent far too long trying to fix the fault within phd, when the issue was a mechanical one

I've given the mount a little 'tune up', to hopefully help things. I've removed some stiction and tightened the DEC backlash a smidge so we'll see. I'll not be able to test anything for a week or two now as I'm away on holiday but hopefully once I get back I can spend bit more time trying to get to the bottom of this.

Phil

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2 hours ago, newbie alert said:

Did you remove the stiction from the locking ring under the come bearing ( can't think of the right terminology, it's been a long day!)

Taper bearing... Just popped into my head...!!

I removed some stiction from somewhere lol. I followed a youtube video for doing RA and DEC. Just loosen some grub screws near the counterweight shaft for the DEC and a similar thing but remove the polar scope for the RA. Took me about 15 min tops :)

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Hi Phil

Looking at the PHD2 Log:

1)  The key to Good Guiding is a Good Calibration.

So trying to guide with issues  Last Cal Issue = Orthogonality  can be a waste of time.

You might have got a good Cal by clearing Dec Backlash first.

2) The sudden dive of RA and Dec in the GA run.

PHD2 was reporting the star position to be moving (without any guide commands of course) as shown in the graph, and the guide star wasn't lost (yellow trace):

 

8thSept.JPG.1efdd5ed13bf11d41fad2d89a17e5943.JPG

 

This can only be due to external influences - a cable snag, the guidescope or camera rotating, Sidereal tracking stopping etc.

Focus was reported to be poor.

Michael

 

Edited by michael8554
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Thanks Micheal. 

There was definitely no cable snagging or camera rotation. I'm wondering if I've somehow managed to damage the power cable whilst moving the mount outside which is maybe causing issues with the RA tracking rate. 

I'll buy another cable to fault diagnose that first. Thank you. 

Phil 

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  • 3 weeks later...

Just an update, I ended up going whole hog and getting a Pegasus Pocket Powerbox Advance, along with a 12v ac to dc converter and the EQ6-r Pro cable so now everything goes through that. Guiding is perfect, I'm getting around 0.5" RMS and I could probably get better with a more accurate align and fiddle with some settings, but tbh it's more than good enough. So thank you, it seems it was the cable/power.

 

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