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Equipment Discussions >> Mounts

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sdh
member


Reged: 10/13/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Gregk]
      #3764708 - 04/23/10 10:38 PM

I have the same mount and have seen this problem and a wide variety of other issues. My tracking / autoguiding success has been hit and miss.

I have a few inputs for you. First, recognize that this mount has no ball bearings in the DEC axis like it does in the RA axis. Second, one of the parameters you can look at in the PHD log is how large the pulse is that is being sent to the mount. I suspect that this number is growing, and growing, and eventually when the mount is 'ready' to move it jerks in that direction. You can determine if this theory is true by looking at the PHD logs for the DEC corrections being sent. So, my theory is, the mount is sticking (consistent with your observation of stiff DEC axis), PHD corrections are growing, and growing until they hit a large number and then it jumps too far. In my case, I limited my PHD DEC corrections to 1000 and rebuilt the DEC axis. I believe limiting the PHD corrections fixed this particular problem.

Also, I cannot tell you that I have perfected my ASGT tracking / autoguiding. I still struggle with this mount and have very inconsistent results. Sometimes perfect, sometimes a mess. Good luck.


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Gregk
Carpal Tunnel
*****

Reged: 11/19/06

Loc: San Tan Valley, Az,
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: sdh]
      #3764892 - 04/24/10 01:04 AM

"I have a few inputs for you. First, recognize that this mount has no ball bearings in the DEC axis like it does in the RA axis."

Mine does! I just had it apart They are small but see link.

My mount seems to stick more when it is cold and lower in latitude.

One thing I noticed is that the end play nut on my RA worm bearing had no grease where it made contact with the outer edge of the bearing surface and created allot of drag Now it is much smoother after adding some synthetic grease

Bearings here for DEC and RA

Edited by Gregk (04/24/10 01:10 AM)


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sdh
member


Reged: 10/13/06

Re: Another CG5-GT "spikes during guiding"-thread... new [Re: Gregk]
      #3764924 - 04/24/10 01:53 AM

Actually, that is not the ball bearings I was referring to. The ones shown in the link are the ones on the worm, yes there are ball bearings there. What I meant was that there are no ball bearings on the DEC axis shaft like there are on RA. Since the shaft is just the shaft dragging on collars that it is inserted in, it is a prime candidate for stiction. When I last had mine apart I used very fine sand paper to try and smooth out these interfaces, but they were pretty rough originally. I should have been more clear about what I meant originally. Thanks for helping me clarify this.

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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: sdh]
      #3765312 - 04/24/10 10:55 AM

Well, unfortunately, I won't be doing any updates any time soon. It appears that the motherboard of my laptop has died on me yesterday. No laptop, no autoguiding. I was going to have dinner, so I closed the lid of my laptop so that it would go into hibernation, and when I wanted to resume, it never came back on again. Every bit of info I've found on the internet seems to indicate my mobo is toast.

As for the CG5 / teflon situation, I did some testing with a relative of mine, who is a retired mechanic, and I might not even buy any teflon. If you take out the plastic washers that surround the aluminum worm gear, the movement is much smoother than with washers. All of the metal surfaces that come into contact with the aluminum worm gear are really smooth. On top of that, the surface areas of the dec shaft and dec housing that come into contact with the aluminum worm gear are much smaller than the surfaces created by the introduction of the plastic washers, creating far less friction than the washers. If I move the dec axis without the plastic washers and use an ever so small amount of Super Lube on the top and bottom of the aluminum worm gear, there seems to be hardly any static friction, unlike when I use the two big plastic washers.

Unfortunately, because of the laptop situation, I cannot test anything yet, so I'm postponing the purchase of teflon for now, because it may well be unnecessary.

Will keep you guys posted.


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vlad10
member


Reged: 04/20/06

Loc: Alicante (Spain)
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3767532 - 04/25/10 02:57 PM Attachment (65 downloads)

I too, should join the "spikers" club with this mount. Really, you would think that with so many of us around, somebody in Celestron would take note and do something about it? As it stands, I would really consider not buying another mount from them - ever.
My graph is so similar to yours DHB001. Does this attachment look similar to you?

I currently have no solution for this and just about feel like pulling my hair out. Or throwing the mount off the terrace. Whichever comes handier at the moment.I cannot believe that 600$ later and autoguiding with this mount is a matter of luck!
For the record I use the 8" reflector, guiding with a converted finderscope and qhy5, imaging with dsi ii. Weight is to a minimum possible, still under 10kg

Edited by vlad10 (04/25/10 02:57 PM)


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: vlad10]
      #3767681 - 04/25/10 04:16 PM Attachment (64 downloads)

Yes Vlad, unfortunately, that graph looks awfully familiar.

As I mentioned before, unfortunately my laptop is now dead, and I cannot proceed to do any more testing at the moment, but I feel really optimistic about leaving the plastic washers that surround the aluminum worm gear out altogether. I've got a pretty strong feeling that they're responsible for the spikes, which imho is static friction.

Provided that the load bearing surfaces in the dec housing and dec axis (see the pictures below and in the following post) are sufficiently smooth, I think that when you use a little bit of grease, chances are the spikes will subside, if not completely disappear.

As you can see, I've got my dec axis fully disassembled at the moment, and while testing by hand, I could really feel a difference between using washers or not. With a washer between the dec axis and the aluminum worm gear, if you move the axis tiny amounts by hand to replicate guide corrections (while applying firm downward pressure on the axis in order to replicate scope load), the motion is jerky. Doesn't matter if I use grease or not (as a matter of fact, grease makes it worse, because the washer will stick to the aluminum worm gear).

On the other hand, if you don't use a washer, and you apply the tiniest amount of grease on the top of the aluminum worm gear, the motion seems to be much, much smoother. Now, I only felt this by hand and cannot yet confirm this through actual guiding performance, but I'm pretty optimistic.

As long as the load bearing surfaces are smooth, and you use a little lubrication, no extraordinary wear should occur, especially since the dec axis really doesn't move that much, apart from alignment and the occasional slewing.


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3767682 - 04/25/10 04:17 PM Attachment (67 downloads)

...

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vlad10
member


Reged: 04/20/06

Loc: Alicante (Spain)
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: DHB001]
      #3767970 - 04/25/10 06:08 PM

You are a braver man than I am. I have yet to stick my hands inside it
fortunately mine is still under guarantee, it will go back to the dealers here in Spain soon, although I am not very optimistic about it...
Thanks for the pics, I can't quite tell which are the plastic washers? If the mount is also used for visual work then chances are they will erode very quickly if you leave them out - I have read the worm gears are made of aluminium!!


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread... new [Re: vlad10]
      #3768115 - 04/25/10 06:52 PM

If you find it hard to identify the plastic washers, it's probably because they aren't in any of the pictures.

I hardly ever do any visual observing. It's mostly photography (or at least that's what I've been trying to do for the last year, lol). So other than alignment and meridian flips, my dec axis doesn't really move that much. And even during aligning or meridian flipping, the movement of the dec axis is never more than a fraction of a circle. Again, as long as the metal load bearing surfaces are smooth and you take care to ensure these parts stay lubed, I don't think the worm gear will wear that quickly. I'm not saying that it won't wear at all, but I just don't think it's going to happen that quickly.

However, if your mount is still under warranty, you're right not to take it apart. Let the dealer sort it out. Though I would be surprised if they would find a solution for this spiking issue.


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Bootlegger
sage


Reged: 01/15/10

Loc: Iceland
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: DHB001]
      #3768863 - 04/26/10 02:42 AM

Hi all.

These graphs you are diplaying are very familiar to me.

My solution was taking the mount appart, relubing and polishing, the mount became better than new and FWHM of stars a lot smaller in images.

Nonni.


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bardo
scholastic sledgehammer
*****

Reged: 09/13/09

Loc: US
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: Bootlegger]
      #3768879 - 04/26/10 03:18 AM

the lxd75's have 2 bearing assemblies for the dec axis and they dont do any better.

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vlad10
member


Reged: 04/20/06

Loc: Alicante (Spain)
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: Bootlegger]
      #3768909 - 04/26/10 04:13 AM

Hi Nonni,
Which parts required polishing?
And does it work for you now?

Cheers


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vlad10
member


Reged: 04/20/06

Loc: Alicante (Spain)
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: vlad10]
      #3770918 - 04/27/10 04:37 AM

Just an update.
I have spend some time last night guiding both east and west, and this time I watched carefully the messages in PHD. My graph would alternate between smooth, spikes and DEC drifting away until disappearing all together, and it is all consistent with the same problem.
Doug is completely right, and this is in fact an identified problem , its called "stiction" and is detailed on the PHD forum. Basically at some point and for mechanical reasons, the DEC axis gets "stuck". If you read the log messages, PHD tries to correct the drift by gradually increasing the length of the pulse. I had my max set to 350 and this was not enough - as a result, the DEC graph would slowly drift away from the graph (how slowly depends on your polar alignment), with PHD desperately logging "S= dur 350ms" and unable to do anything about it. I then increased the max to 1000ms. As a result, when it reaches about 700-800ms it finally manages to "unstuck" the dec axis and wham! - it throws it to other side of the line, usually this is because the inertia of the unblocking axis who's been accumulating momentum. Sometimes its stuck less bad, and it manages to release it once it reaches about 400-500ms.
Solution: NONE with the software. In my case is still under warranty, so back it goes, but I imagine its what Nonni said, relubing, polishing, and also possibly changing any bits inside that might have deformed (anything plastic sound like a candidate for me )
I hope this helps.


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Tapio
Pooh-Bah


Reged: 09/24/06

Loc: Tampere, Finland
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: vlad10]
      #3770944 - 04/27/10 05:44 AM

Let me tell my experience, although with different mount.
I have a HEQ5 Pro and I wasn't too happy with DEC autoguiding.
It seemed random too, sometimes worked okay but more often it was useless no matter what I did.
So my solution now is to do as accurate polar alignment as possible (with the help of WCS and webcam).
This takes about 10 minutes before I star imaging and now I can skip dec autoguiding altogether and still have managed 4-5 min subexposures which is pretty much what I need in my moderately light polluted skies.


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DHB001
sage


Reged: 07/07/09

Loc: The Netherlands
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: Tapio]
      #3816762 - 05/20/10 03:03 AM

*UPDATE*

It's been a while, but my laptop has been fixed and last night the weather was finally decent enough to do some testing. I apologize for the delay. As mentioned earlier, I wanted to see how guiding performance would be without the plastic washers that surround the aluminum worm gear.

My first bit of testing was on M51 , which is the object that caused me so much trouble with spikes a few weeks ago. M51 for me has now passed the meridian, but is still practically right above my head in zenith. The dreaded spikes in the dec guiding turned out to be still present, albeit nowhere near as frequent as a few weeks ago. So maybe removing the plastic washers has helped somewhat. Maybe not. I need to do some more testing to be sure. Although the frequency of the spikes has been lower, it was still not good enough for imaging, unfortunately.

However, when I later aimed my scope at M13, an object that is high in my night sky, but not as close to my local zenith as M51, guiding became extremely smooth. No spikes during the 30 minutes I tested (before I called it a night). Dec and RA guide graphs smoothed to +/- 1 pixel in PHD, which approximately corresponds to an equal amount of arcseconds (according to CCDcalc).

Hopefully, I can put in a little more testing in the coming nights. But the initial conclusion of last night was that omitting the plastic washers seemed to have made guiding less spikey in zenith, but still too unreliable for decent imaging. On the other hand, guiding in an area a bit further removed from zenith appeared to be trouble free (though admittedly, 30 minutes is too short for any definite conclusions).

To be continued...


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philming
member


Reged: 04/18/11

Loc: France
Re: Another CG5-GT "spikes during guiding"-thread. new [Re: DHB001]
      #4528470 - 04/19/11 08:39 AM

Hi there !
Very interesting post and test i may say.
Just a question. Did you have those spikes before removing the washers when shooting M13 ?
I'm in the process of regreasing my CG5 too, and was wondering about geting the Teflon washers.
What I have noticed when reassembling the mount was as follow : The two large washers you are refering too seem to hurt the rotation of the axis indeed. When puting it all back together, i did as i felt right : put one washer on top and at the bottom of the teethed crown. And it seemed like they wouldnt actually fit on top (ref. to your second picture). When reassembling the shaft in the housing, the washer would simply get crushed, it had been just to big.
I thought i had it wrong and was supposed to put both of them, on top of one other at the bottom of the shaft. Seemed right so far, but removing them alltogether might be a better idea.
That leads to another question : I have a very hard time reassembling this part. Seems like if I dont slide the axis very smoothly and very upright into the housing, it's going to get stuck, no matter how much grease I put on it. It's mostly the crowned gear that gets stuck, and is a real pain to remove. Did you notice that as well ?

Regards,

PS. Sorry off topic question. How can I get notified when a response is posted on topics I post in ? Haven't found the option so far...


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