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Atlas EQ-G PE Data and Questions

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#1 hoa101

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Posted 27 April 2013 - 11:43 PM

I have a new Atlas mount that I took for a spin tonight, but I noticed a couple things that are a little strange.

First, the RA axis turns freely when the counterweights are to the East, but there is a decent bit of stiffness/binding when on the opposite side. It is actually stiff enough that the head will stay in the 90-degree position (counterweight bar parallel to the ground) with the clutch disengaged - but only on the one side.

Second, here is my PE harmonics. What is the 5th worm harmonic and why is the magnitude of the error so huge (about 6 arc-second)? Any information is appreciated, because I am not having much luck with google.

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#2 hoa101

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Posted 28 April 2013 - 08:35 AM

And here is the periodic error graph. Whatever is causing this 5th Harmonic error is just killing the tracking capability. Each one of the "mini-peaks" corresponds to this frequency.

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#3 rmollise

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Posted 28 April 2013 - 12:04 PM

25 seconds peak to peak is killing you? Are you trying to work unguided? If so, forget it. This is a fine mount that works incredibly well for GUIDED imaging. ;)

#4 hoa101

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Posted 28 April 2013 - 12:16 PM

No, the overall peak-to-peak error is not at all the problem. I am referring to the short 95 second period that I mentioned in the post. The speed at which the error varies in this period means by auto-guider is not able to perform well at all.

If I has seen this in other HEQ6 data online, I would write it off to not being a top-of-the-line mount. But this is not a problem I have not been able to find anywhere. It is reminiscent of the infamous CGEM 8/3 error that makes imaging with those mounts impossible sometimes.

According to the EQMOD project:

"...if a significant signal appears with a period of 300s we might also see harmonics at 150s (2nd harmonic), 100s (3rd harmonic), 75s (4th harmonic) etc. We would usually expect the signal magnitude to diminish with with successive harmonic. If you find that odd harmonics are particularly prominent this might indicate that the associated mechanical part is being restricted in its movement."

In other words, I do not understand why the 5th worm harmonic would have almost the highest response of any frequency. That makes no sense at all.

#5 hoa101

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Posted 28 April 2013 - 12:53 PM

This should make is clearer. The top graph is more similar to the error plots I've found online. This excludes the 5th harmonic. The lower two show what happens when you include it, and the isolated period respectively. It should be pretty clear why my guiding is not working too well.

If anyone knows if this can be adjusted, please let me know. I am going to hopefully speak to the vendor this week about it.

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#6 zerro1

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Posted 28 April 2013 - 01:34 PM

but there is a decent bit of stiffness/binding when on the opposite side. It is actually stiff enough that the head will stay in the 90-degree position (counterweight bar parallel to the ground) with the clutch disengaged - but only on the one side.


if you have binding or stiffness, how accurate is the PE graph going to be? Solve the binding/stiffness issue, then look at the PE. I have an Atlas that I replaced "All" bearings in it because the previous owner had completely packed hard the bearings with "white lithium". I went through all the adjustments and still wasn't very pleased. I sent it off to Ed Thomas... Needless to say but I will; there is now NO binding or stiffness anywhere in that mount.

The Atlas is still a mass produces mount with the flaws of low QC when compared to the high end, hand built mounts. Assembly is per procedure, not as a single entity! My guess on the binding is that either something is adjusted too tight or that the internal spacers are incorrect.

If I could afford a higher end mount, I would have gone that route. I could even spend the money on the upgraded aftertmarket gear that is supposed to reduce PE in these mounts and I'd still be under by a lot of what it would cost to go to the high end mounts. A lot of people that get the Atlas basically look inside the box, close it back up and send it to off to get hypertuned. Atlas mounts are sensitive to ballance, I ballance mine so that if I crack the RA clutch loose, it gently falls to the home position.

#7 hoa101

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Posted 28 April 2013 - 01:56 PM

I guess my question is whether I am being too picky -

Is it reasonable to expect that, for example, the RA axis is free from binding out of the box? Or does everyone chalk that up to "mass produced mount" and take it apart?

At what point do we have warranty work done? I don't expect sine-wave PE on an Atlas, but my issues seem a little beyond what we should allow for a brand new mount...

#8 rmollise

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Posted 28 April 2013 - 02:56 PM

No, the overall peak-to-peak error is not at all the problem. I am referring to.


OK, I just don't see it in your PE graph. But I do see that you mention significant stiffness in one orientation of the RA axis. You need to do something about that before you worry about PE, I would say. If you cannot balance the mount in RA, something is wrong--if you've got a scope on the mount. Not moving without a scope or counterweight is normal.

#9 hoa101

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Posted 28 April 2013 - 03:08 PM

I meant without scope - just counterweight bar deployed. It's not really that bad, just strange that there is friction on one side but not the other.

The main issue is the error with 96 sec period. Another thing I noticed... there is no peak in my PE data at the fundamental worm period. Just the transfer gear and the 5th worm harmonic. I wonder why that would be.

#10 Raginar

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Posted 28 April 2013 - 04:57 PM

I think that's what he's saying, you need to have weight on it to get an accurate measurement.

#11 hoa101

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Posted 28 April 2013 - 05:10 PM

Ah, I may have been confusing people. I obviously took PE data with my guide scope and whatnot hooked up. But the friction is especially noticeable with no weight on the mount at all. With the scope on there, it is noticeable in that you cannot balance it well when facing one direction. Had to flip it the other way.

Anyway, I think I may just take the advice above and have it hypertuned. I think the graphs are a bit ugly but with some tweaking it might be acceptable for imaging.






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