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Can an LXD75 run a teensy bit slow (or fast)?

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#1 MtnGoat

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Posted 20 April 2009 - 11:03 AM

I've been trying to figure out the source of a slight drift over time in my images.

I've got the polar nailed (pier mounted) and get the 'less than 5'' messages each time I do an alignment. This is supported by the fact that I get very little if any DEC drift over any period of time.

However I am getting RA drift, which to me seems to indicate a slight speed issue with the RA drive.

It is possible I need to dial the RA drive speed up or down a percent or two? (haven't analyzed if it appears fast or slow yet, I just know I have RA drift).

Is this something I would deal with using the 'tracking rate' field in Autostar, or by changing the gear ratio a tiny bit?

#2 JAT Observatory

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Posted 20 April 2009 - 11:41 AM

There is a menu item that allows you to set the % of sidereal tracking speed. You need to change the % number to increase or decrease the tracking speed.

#3 jgraham

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Posted 20 April 2009 - 11:48 AM

Also, make sure the drive rate is set to sidereal and not lunar.

#4 MtnGoat

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Posted 20 April 2009 - 12:12 PM

thanks for the tips so far. I'll make sure I check what my drive rate is set to.

am I crazy in thinking that the rate could need a tiny bit of tweaking? I mean...it's all digital timing with very accurate clocks and known gear ratios..how could this be?

#5 sang33ta

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Posted 20 April 2009 - 01:34 PM

Make sure your weight is balanced in both axis if it's out it'll drag or pull.

#6 gordianknot

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Posted 20 April 2009 - 02:17 PM

I agree about checking balance. My first guess is that something is slipping.

#7 MtnGoat

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Posted 20 April 2009 - 02:56 PM

yes, checked the balance. if anything, it's a bit too balanced! I was going for the slightly E heavy approach, but backed off on it when I started noticing this.

#8 Skywatchr

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Posted 21 April 2009 - 08:54 AM

The tracking rate can be affected by a small amount of extra friction somewhere slowing it down some. Could be the lube on the worm isn't spread out enough, or a bearing is dragging (polar bearing too tight), or something rubbing that shouldn't be. Being heavy on the East will slow it down a little unless it's only about an ounce or so. Just enough to take out any flex.

Jeff






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