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frugal

PHD2 Drift Align - trend line doesn't change

63 posts in this topic

It is a clear night at last. I do have to go to work in the morning, but I have a couple of hours to try to crack this PHD issue. So I point at the Southern sky just by the Celestial equator:

58ffc7b512b39_Capture01calibrationstar.thumb.PNG.c409b993aeaa977437a9f3cf8b49efae.PNG

I run the Calibration on this star and I get a fun new error that I have not had before:

58ffc7b676272_Capture02CalibrationError.PNG.641e97cffefd513735a097fea7a2def3.PNG

hmmmm....

I am currently running the guiding assistant to see if that helps.

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what are your dec and ra rates in eqmod? I think off the top of my head they should be 0.5 to 1.0.

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2 hours ago, spillage said:

what are your dec and ra rates in eqmod? I think off the top of my head they should be 0.5 to 1.0.

They are both 0.5

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Shouldn't worry too much about that one, it won't stop guiding working.

Try to avoid crossing the Meridian while in the process of calibrating and sorting stuff.

Dave.

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I made that I was on the West side of the Meridian, so I had 11 and a half hours to get the calibration sortedūüėČ

The PHD docs just state that the discrepancy between RA and Dec rates indicates a problem, but gives no clues as to what kind of problem it might be. The Dec rate at 7.4 is pretty close to the rate it should be for 0.5 guide rate, so I am assuming that the problem lies in RA.

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If you look closely at the calibration graph you can see that the eastbound leg overshoots by a long way and also that the first few readings on the westbound leg are very close together before they spread out to a more normal, even spacing. Tht accounts for why it takes 18 steps for RA and only 13 for Dec. My guess is that you had slewed the scope eastwards to the calibration position which introduced backlash into the RA axis. So it took a while to get moving westwards. Either that or the worm was binding or you had stiction or an imbalance that caused a lag at the start of the westbound leg.

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So if I nudge the scope a little West before I start the calibration and the problem goes away then it is probably backlash. If I still have the problem then it is more likely to be balance or binding?

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4 minutes ago, frugal said:

So if I nudge the scope a little West before I start the calibration and the problem goes away then it is probably backlash. If I still have the problem then it is more likely to be balance or binding?

I had exactly the same fault show in PHD2 on my AZ EQ6, which was when I finally decided to tackle what I considered to be pretty excessive backlash from the factory.  Spent about 3 or 4 hours carefully tuning, adjusting and lubricating the worm wheels until there was minimal backlash but no binding (be sure to check warm and cold) and the problem went away for me, although it could have been unrelated it has not happened again since.

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Just now, RayD said:

I had exactly the same fault show in PHD2 on my AZ EQ6, which was when I finally decided to tackle what I considered to be pretty excessive backlash from the factory.  Spent about 3 or 4 hours carefully tuning, adjusting and lubricating the worm wheels until there was minimal backlash but no binding (be sure to check warm and cold) and the problem went away for me, although it could have been unrelated it has not happened again since.

I have not worked up the courage to tear apart £1,400 worth of mount yet. I have read the stripdown document and it scares me somewhat. I am the sort of person who always ends up with a couple of screws left over after that kind of operation.

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9 minutes ago, frugal said:

I have not worked up the courage to tear apart £1,400 worth of mount yet. I have read the stripdown document and it scares me somewhat. I am the sort of person who always ends up with a couple of screws left over after that kind of operation.

Hi

I would check balance first and in all three axes (RA, DEC and vertical). Get it perfect then adjust the counterbalance weight to make the mount slightly east heavy.

Louise

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1 minute ago, frugal said:

I have not worked up the courage to tear apart £1,400 worth of mount yet. I have read the stripdown document and it scares me somewhat. I am the sort of person who always ends up with a couple of screws left over after that kind of operation.

You don't actually have to do the full strip to reduce the backlash, it's pretty simple and only a few allen headed bolts.  Although if you're not confident it is best left as it is.

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44 minutes ago, frugal said:

I have not worked up the courage to tear apart £1,400 worth of mount yet. I have read the stripdown document and it scares me somewhat. I am the sort of person who always ends up with a couple of screws left over after that kind of operation.

I believe these are know to the trade as weeee bolts.

Thats the noise you must make as you throw them over your shoulder. 

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Hi frugal,

Balance the scope as Louise suggests and get  imaging !

Michael

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