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Atlas question - RA off by 45 degrees?

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#1 Alwaysusa

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Posted 12 August 2010 - 02:06 PM

Hey all,

Another night working with my new Atlas mount and I noticed something troubling.

I set everything up correctly (learned from my previous mistakes with Benny Hill).

Last night I set everything up correctly, polar aligned accurately, then went for a 3 star alignment. For the first star I chose (Vega), the scope went to the wrong RA, by about 45 degrees. I centered Vega then went for the second star, which was again a good ways off. The same happened with the third star, which I centered. The alignment failed with an error message that told me the RA was off by 45 degrees (I am paraphrasing, I hope someone recognizes the error message).

Turn off the mount, reset to home position, try again.

The same result.

Turn off the mount, reset to home position, try again.

Repeat x4.

On the eighth attempt, it aligned correctly. No data was entered ANY differently, and I used exactly the same stars each time.

The ONLY thing I did differently on the last attempt was to manually move the setting circles (just the circles, not the axis) to RA 0 and Dec 0 when I put the scope back into the home position before it started the 3 star align.

Does the mount 'read' the setting circles or are they purely manual? I had assumed they were manual and there just for me to use after polar alignment, but as nothing else changed I'm out of ideas as to why the slews were off every single time. It's the only variable that changed between success and failure.

Once aligned, it was perfect all night, but it was pretty frustrating.

I did a factory reset after the third attempt, but it didn't help. I did not do a factory reset before the successful attempt (other than turning the mount on and off, which I did after ever attempt).

So I'm stumped. I'm hoping someone has had a similar experience.

#2 rmollise

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Posted 12 August 2010 - 04:20 PM

No. The mount doesn't know pea-turkey about teh setting circles.

#3 Alwaysusa

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Posted 12 August 2010 - 07:05 PM

Yes, that's what I assumed. Well damn. I have no idea what's up with the mount then.

#4 Garry

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Posted 13 August 2010 - 12:22 AM

Having "set everything up correctly " and all data entered
exactly the same and on the 8th time success, the RA clutch
could be slipping. What do you have on the mount load wise?
Is it balanced well or is the mount stiff and hard to balance because of that? Is the red power led constant or
does it pulsate when slewing RA?

The clutch pads sometimes have grease on their contact surface with the worm drum that can cause slippage even when cinched tight.

You did the set up 8 times so that your moving and clamping
could have thinned the grease to the point that your 8th clamping force was enough to hold the RA.

Hope your solution is as easy as this: Clutch Adjustment

Garry

#5 vinnie

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Posted 13 August 2010 - 01:50 AM

1. Forget anything to do with the RA setting circle. It has no relevance to an alignment.

2. Are you sure that the stars you used for alignment were in fact the stars that were intended?

3. By attempt #8 you might have been looking at different stars but thinking they were the same?

4. FWIW the park position is at Dec 90° not Dec 0° and the park position has no relevance to RA

#6 rmollise

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Posted 13 August 2010 - 07:15 AM

Yes, that's what I assumed. Well damn. I have no idea what's up with the mount then.


I'd look at my setup procedure. That you have home at 0-degrees instead of 90-degrees says you do not quite have it down yet.

#7 Alwaysusa

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Posted 13 August 2010 - 02:55 PM

Well the degrees are arbitrary as the setting circles are manual. I just set them to 0 hoping it might make a difference. As noted though, the setting circle position does not affect the goto.

Once polar aligned, my home position is supposed to be counterweight bar straight down, and RA clutch to the left, directly above the on/off switch. At least this is what worked for me before, and eventually the other night (it's also the position shown in the manual).

I can see how being a slightly incorrect in this home position may cause the first star to be a little off, but the margin was very large each time until the 8th try, when it hit Vega dead on.

I guess it is possible I was looking at the wrong stars, though I specifically chose Vega first as it's one of the first stars out, and Ceph as Cassiopeia is unmistakeable, even late at night.

The most confusing thing is that if I didn't change anything between attempts, why would the final alignment work? The only variable that change was the settings circles, so effectively nothing changed.

One other thing to note is that when I turn the mount on and off, the time zone is always at +8 hours, so I have to change it to -8 hours (I am in California). I would think that the time zone would stay in memory, as does the lat/long but apparently not?

The other thing is that the LAT scale is SO far off. I have to set mine to 29 degrees instead of 34.

So either I'm making some fundamental error in my set up (yes, this is likely I know) or there are just issues with the mount.

Can a store check the polar alignment and gotos during the day? I'm trying to figure out the best way to do a sanity check before the next star party I can attend, which is now not until September.

#8 David Rosenthal

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Posted 13 August 2010 - 03:27 PM

1. Do you level the tripod before starting the GoTo alignment?
2. Have you checked the collimation of the Polar Alignment Scope

#9 Alwaysusa

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Posted 13 August 2010 - 03:52 PM

1) I do, yes. I use a torpedo level now as someone suggested the bubble level on the mount may not be accurate.

2) I have adjusted the PAS for cone error, so the center of the PAS stays on a given focal point when rotated. Is that what you mean?

#10 rmollise

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Posted 13 August 2010 - 04:29 PM

1. Do you level the tripod before starting the GoTo alignment?
2. Have you checked the collimation of the Polar Alignment Scope


Neither of these things will cause such egregious problems. What will? Assuming the mount is properly placed in home position, centering the wrong alignment stars.

#11 AJinYYC

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Posted 13 August 2010 - 04:40 PM

"One other thing to note is that when I turn the mount on and off, the time zone is always at +8 hours, so I have to change it to -8 hours (I am in California). I would think that the time zone would stay in memory, as does the lat/long but apparently not?

next time you try to align. when you input your time zone...go with me on this, when you change the + to a - use the right hand arrow key to do this... not the left one... bottom right of the keypad. once i did that... it stayed in memory and my alignment worked... seems there is a bug in the software version.. you are using v 3.24 i'm guessing?

Now when i start up, it is -0700 instead of reverting back to +0700 like it used to.
I read this on another forum---- and so far it has seemed to make the difference, but that being said ive only been able to do a dry run alignment...during the day with stellerium as a guide, (bad weather) but instead of going to the opposite side of the sky as arcturus and getting the "RA is 45 degrees off" message, it said the alignment worked....

Let me know if it made any difference for you... and ill post as well when i get a chance to do a full alignment at night.

cheers,
AJ

#12 David Pavlich

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Posted 13 August 2010 - 09:20 PM

Here's one other tip that might help. When it's still twilight have everything set up and ready to go. The brightest star in the west is Arcturus at about 50° above the horizon and in the east is Vega about 70° above the horizon. Watch for these two stars to appear as they will be the first stars of the evening. When you see them, don't forget their positions. Watch for the Big Dipper to appear. Dubhe is the upper most star in the bowl and lined up with Merak, it points to Polaris. You will use Arcturus and Dubhe in the west for your initial 2 star alignment and immediately slew to Vega in the east for you eastern star. This is what I do at outreach events so that I can get aligned as quickly as possible. Gotta' keep the viewers happy. :grin:

This will eliminate the wrong stars as the problem. Good luck!

David

#13 soreneck

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Posted 13 August 2010 - 09:47 PM

As an EQ6 owner (same as Atlas), I can attest to occasional strange issues similar to this one (general pointing orientation being *way* off). Drove me crazy for a while.

Turned out to be caused by the handset, which would occasionally forget what time zone it was in (despite the fact that it would retain the correct location and other settings).

Fixed this with an update to the latest available firmware, hasn't happened since.

Cheers,
Adam

#14 rmollise

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Posted 14 August 2010 - 08:10 AM

As an EQ6 owner (same as Atlas), I can attest to occasional strange issues similar to this one (general pointing orientation being *way* off). Drove me crazy for a while.

Turned out to be caused by the handset, which would occasionally forget what time zone it was in (despite the fact that it would retain the correct location and other settings).

Fixed this with an update to the latest available firmware, hasn't happened since.

Cheers,
Adam


Yep...good catch...update to 3.27 and these problems should be banished.

#15 AJinYYC

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Posted 14 August 2010 - 05:37 PM

so why has nobody figured outhow to update the handcontroller on a mac??!? im stuck with v3.24 until i can figure this out..

#16 Alwaysusa

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Posted 15 August 2010 - 05:02 PM

I am also on the Mac and will find a way to update the controller as I am indeed using a slightly outdated version of the software (3.24).

Thank you all for the help. I'm going out this week so I should be able to test the set up again. I'll try that tip AJ - thanks for the heads up.

- Adam

#17 bluedandelion

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Posted 18 August 2010 - 12:31 AM

so why has nobody figured outhow to update the handcontroller on a mac??!? im stuck with v3.24 until i can figure this out..


I am a Linux user primarily (using it right now), but I have learned that some battles are not worth fighting. Life is too short for that. So for all purposes related to imaging and observing I use Windows - I have dual boot on all machines at home. One solution would be to borrow a laptop from an acquaintance or install some version of windows via bootcamp to upgrade the hand controller. I have not tried bootcamp myself - you will have to experiment.

Ajay






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