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PHD "cyclical" Dec errors

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#1 snoraste

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Posted 09 December 2019 - 08:41 PM

I've been using my NEQ6 with PHD2, and a couple of nights ago I see a graph that clearly shows a short-frequency, cyclical dec error. I have recently re-lubed the Dec axes, and (attempted) to fine tune it again as per astro-baby. Anyone had similar experience?

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#2 snoraste

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Posted 09 December 2019 - 08:51 PM

jpeg:

guiding.jpg



#3 Gipht

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Posted 09 December 2019 - 10:32 PM

My graph looks somewhat like this when there are strong variable winds.  I have an 8" reflector, so it reacts to gusts.



#4 whwang

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Posted 10 December 2019 - 01:20 AM

In addition to winds like what Gipht mentioned, another possibility is excessively large Dec backlash.



#5 mxpwr

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Posted 10 December 2019 - 01:40 AM

Peak to peak of more than -1.5" to 1.5" seems quite excessive.

#6 dayglow

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Posted 10 December 2019 - 02:58 AM

The graph has the look of backlash to me also.

Have you tried running the PHD2 Guiding Assistant tool ?  It tests for and reports DEC backlash.

-- David F.



#7 snoraste

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Posted 10 December 2019 - 07:25 AM

I did run the guiding assistant. the backlash was about 780ms which I then accounted for in PHD. It was not a particularly windy day, so I don't think it's the wind (I was using my SV105T which is fairly compact) and I checked all the cables to make sure there are no snags. It seems more like gear slippage, no? I did try to tighten up the contact between the Dec motor and the gear. Maybe that? The thing is that the error is happening in far less than a full cycle of the Dec motor/gears. Feels like there's something loose. 



#8 ELDavis

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Posted 10 December 2019 - 08:48 AM

I would think if this was from wind you would see similar large excursions in RA. Perhaps your Dec clutch isn't fully tightened, or your balance is off.



#9 fmeschia

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Posted 10 December 2019 - 04:15 PM

The graph shows a definite time correlation between RA and Dec drifts. To me, this point to a general mount “disturbance”, which could be due to wind or cable drag.

Francesco



#10 snoraste

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Posted 10 December 2019 - 04:36 PM

I did notice the correlation also, especially on my longer guide time. But the disturbances in RA is far less than DEC, so something disturbing DEC more than RA? I will double check the snags. 



#11 guyroch

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Posted 10 December 2019 - 05:34 PM

If you in guide in RA only as a test, does it show disturbances in RA still?  If not the disturbances are introduced by the DEC axis...might give you a place to start looking.  

 

Good luck.

 

Guylain



#12 snoraste

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Posted 11 December 2019 - 08:46 PM

good point -  I'll test it when I get some clear skies




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