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Equipment Discussions >> Mounts

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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5740529 - 03/18/13 11:34 AM

Quote:



Much better choice than a CGEM DX, congratulations!




Yup. A buddy of mine has both, and sets them up side by side. The CGEM-DX can't compete. I've not owned a CGEM of any flavor, but I've owned a few Atlases and they were no competition for my CGEs.


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: jrcrilly]
      #5740738 - 03/18/13 01:38 PM

Hi,
I would buy an AP right off but Its way above what I can come up with.

I really like the Celestron firmware and I think If I got a good CGEM DX like I had the first time I would be happy. So if the CGE is better I will be happier. I don't mind if I have to do some hypertuning to it. I have taken apart every mount I have ever owned and done some tuning and improved the performance.

The G-11 made me lower my expectations on unguided imaging. I finally got low PE but PEC needed to be turned on to stop the RA drift. And since I had to go to the trouble to hook up my computer each time and retrain the PEC and check it, I might as well do guided imaging instead.

If I can get the PE low enough I will be able to do unguided imaging with the CGE but I'm not expecting it to get that low. But I will try to get it lower just for good guided imaging.

I don't understand what a dead zone in the CGE's DEC means. I can't find any information on line about it so far except one thread about balance in the DEC. on the CGE yahoo group.
I couldn't imagine any mount to be more criticle with balance than that G11 I had.

I expect the CGE will have great goto's like all the CGEM DX mounts I had did as long as I use the most recent updated firmware. I have lowered my expectations on PE and realize that I dont have enough money to afford unguided imaging but I'll probably get an aeroquest worm gear to see if its possible.

I did consider a TAK but I couldn't find any used anywhere near what I could afford and this CGE popped up first.

I have been reading every review I can find on the CGE and I think I will be happy with it.

neilson


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5740782 - 03/18/13 01:58 PM

Quote:

I don't understand what a dead zone in the CGE's DEC means. I can't find any information on line about it so far except one thread about balance in the DEC. on the CGE yahoo group.




The "dead zone" (I'm really not sure what else to call it) is something that I have run into recently but have now talked to or heard of a number of people with the problem including the two CGEs that I have. I have seen it in both untuned and tuned mounts. I am sure that it varies with each mount, but I suspect that it is systemic in the CGE mount overall.

Essentially what happens is that in a large zone of the sky corresponding to your latitude (+/- up to 30-40 degrees), when the DEC is in a position that it is symetically balanced there is a problem where, when you change directions, the axis makes a quick jump forward and then stops and then starts moving in the choosen direction at the choosen rate. At high speeds it is not visible but at speeds below 5 it becomes very obvious. As far as I have been able to determine it is related to backlash between the worm and the worm wheel. Off-balancing solves the problem, but since the problem is in DEC, a dynamic off-balancing system would be necessary to always take care of it and that gets even more difficult if the problem occurs over a large swath of the sky. It is likely a combination of a mechanical issue and an electronic issue where the mount starts moving with a small power surge (similar to anti-backlash) in order to overcome any stiction between the gears.

Ideally, reducing the backlash would help, but CGE worm wheels are rarely round (like many gears) so that it is not possible to reduce the backlash sufficiently to take care of it. In addition, if the gears are too tight that leads to other problems. My thinking at this point is that a spring loading system for the worm is the only solution. This also explains to me why Celestron went with a spring-loaded worm in the DEC axis only when the CGE Pro mount came out. While spring loading can be accomplished, it is not easy and the only solution I have right now is fairly inelegant.


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: EFT]
      #5740841 - 03/18/13 02:41 PM Attachment (10 downloads)

Hi ED,
Thats very interesting. And I think your reasoning of why the DEC only on the Pro is spring loaded is valid. I will have to look out for that. Thank you.

My 9.25 Edge is balanced in every direction. I have a laser and 9v battery powered brightness controller for my illuminated reticule on the opposite side of my finderscope for balance. On the front I have a small one pound weight. The hole in the weight is off centered to one edge. A small rod pointing down holds it. I can adjust the tightness so I can tilt it to one side or the other to create a slight off balance if needed. It can also be loose and would switch sides when going over the meridian. Maybe something like this would work. It could be made different ways but the weight comes off my LX200R 10" ota"s sliding weight set. Here is a pic below

neilson


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orlyandico
Post Laureate
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Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5740866 - 03/18/13 02:52 PM

I don't think that dead zone will be a huge issue. You would only be imaging 1-2 objects per night anyway. So point to your object, then move the weight to ensure that the DEC is heavy on one side...

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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? new [Re: orlyandico]
      #5753103 - 03/24/13 01:22 AM Attachment (6 downloads)

Hi Everyone,
I got my almost used CGE mount today. I opened the boxes. It looks brand new. No Scratches or scuffs or faded paint. Its been packed in the box for years after only a few uses. This mount is heavy duty, solid. No cheap plastic here. No corners cut when they built this mount.

Theres no stiction. I love the way it finds the home spot all buy itself on startup. I did a 2+4 alignment then did a goto to a DSO and it was dead center in my 12mm reticule eyepiece using my Edge 9.25 ota. with Orion 80mm guidescope, 2" flip mirror, Canon T1i camera and Dsi IIc. All about 34lbs load. I had updated the firmware to the most recent version.

Then I wanted to try an initial PE run to see just how bad this mount was. It was just over 3 arc seconds total PE.
I am very happy about these first results. I will do more tests but they should all be good after this. This mount is very quiet. When it slews on high speed it just makes a little humming noise.

I want to thank all of you who gave me this great advice. I couldn't have done better. I was afraid to buy something used but I was wrong. Now I have a mount that performs great and is practically brand new for only $1,629.
I know it's still too soon to be 100% sure but I think this mount is the one. I have not done any imaging yet but will soon. This is the best mount I have ever owned, and I didn't have to do anything to it.

neilson


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orlyandico
Post Laureate
*****

Reged: 08/10/09

Loc: Singapore
Re: Replace GM-8 Gemini I w/ Atlas? new [Re: neilson]
      #5753252 - 03/24/13 04:28 AM

Congratulations!

Souns like you must have gotten a very good one if is it 3" p-p PE out of the box.. Celestron only warrants +/- 5" for the CGE Pro (and 3" p-p with PPEC enabled). The old CGE had no periodic error guarantee at all..


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neilson
professor emeritus


Reged: 08/22/10

Re: Replace GM-8 Gemini I w/ Atlas? [Re: orlyandico]
      #5753514 - 03/24/13 10:00 AM

Hi,
I was amazed my PE was so low. I havent tried the PEC yet but will soon. I wont have to do weeks of testing and adjustments on this mount. I will finally get to go back to imaging. This time long exposures will be easy and with round stars. Now I will be able to take my imaging to the next level. I am very pleased.

I just noticed theres a CGE on cloudy nights classified that looks nice and clean and even has the orange knobs. The price looks good too.

neilson

Edited by neilson (03/24/13 06:16 PM)


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