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Technical differences between CGEM and AVX mounts

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#1 Ziguy

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Posted 13 February 2020 - 11:56 AM

I read many "CGEM II vs AVX" threads but I could not find one that discuss the technical differences. Particularly the kind of gear used, their size and other difference like this.

 

Edit: Please note the title should say CGEM II 


Edited by Ziguy, 13 February 2020 - 12:31 PM.


#2 bobzeq25

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Posted 13 February 2020 - 01:02 PM

A major difference is that the AVX only uses a simple bushing on DEC, the CGEM II uses an actual bearing.  Some people have found that bushing to be a problem for imaging.


Edited by bobzeq25, 13 February 2020 - 01:02 PM.

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#3 WadeH237

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Posted 13 February 2020 - 05:12 PM

The differences go way beyond the bearings.

 

The AVX is a descendant of the CG-5, which itself was a clone of the original Vixen Great Polaris.  The CGEM is mostly a copy of the Takahashi EM-200.  Complete and total different designs.  The only thing that they share is a hand controller.



#4 Ziguy

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Posted 13 February 2020 - 06:36 PM

The differences go way beyond the bearings.

 

The AVX is a descendant of the CG-5, which itself was a clone of the original Vixen Great Polaris.  The CGEM is mostly a copy of the Takahashi EM-200.  Complete and total different designs.  The only thing that they share is a hand controller.

Could you please elaborate? Unfortunately, I don't know the difference between the Vixen Great Polaris and the EM-200.


Edited by Ziguy, 13 February 2020 - 06:36 PM.


#5 WadeH237

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Posted 14 February 2020 - 10:19 AM

Could you please elaborate? Unfortunately, I don't know the difference between the Vixen Great Polaris and the EM-200.

The easiest answer about what is different is "everything".

 

If would help if you could ask specific questions.  If you don't have specific technical questions, perhaps you could tell us why you want to know.  That would helps us to give a meaningful answer.



#6 Ziguy

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Posted 14 February 2020 - 12:02 PM

The easiest answer about what is different is "everything".

 

If would help if you could ask specific questions.  If you don't have specific technical questions, perhaps you could tell us why you want to know.  That would helps us to give a meaningful answer.

 

I don't know much about how mount works internally so it pretty difficult to ask specifics questions. But like I said, I'm looking to stuff like the gears used, their size and other difference like this.

 

I don't know but unless I'm really jaded, I should be able to say a little more than "everything is different" if someone ask me the differences between a Corvette and a Civic!


Edited by Ziguy, 14 February 2020 - 12:10 PM.


#7 bobzeq25

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Posted 14 February 2020 - 12:19 PM

I don't know much about how mount works internally so it pretty difficult to ask specifics questions. But like I said, I'm looking to stuff like the gears used, their size and other difference like this.

 

I don't know but unless I'm really jaded, I should be able to say a little more than "everything is different" if someone ask me the differences between a Corvette and a Civic!

The following is for traditional imaging only, visual or EAA is a _completely_ different ballgame.

 

I don't know the details, but typically the differences between a $900 mount and a $1650 mount involve (rough order of importance):

 

Better, bigger bearings.  Bigger more precisely made gears.  Bigger shafts.  Bigger motors (a cheap part of the mount, manufacturers have been known to use the same motor in different mounts for simplicity).  Better electronics.  A sturdier case to hold everything rigidly.

 

Price is an excellent guide to mount quality.  There simply is _no_ comparison between these two mounts if you're planning on doing traditional imaging.  One costs almost twice as much as the other.  The AVX is not some mystical bargain, it's a very inexpensive mount, perhaps the least expensive that's somewhat suitable for traditional imaging with a telescope.  Depending on the specific example you get, it may be suitable for a small refractor for imaging.  Some find it so, some not.

 

You don't actually need to know details to know that a $50,000 Corvette is _way_ faster and better handling than a $20,000 Civic.  This is similar.


Edited by bobzeq25, 14 February 2020 - 12:25 PM.

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#8 Ziguy

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Posted 14 February 2020 - 03:06 PM

 

You don't actually need to know details to know that a $50,000 Corvette is _way_ faster and better handling than a $20,000 Civic.  This is similar.

Yeah but in many threads, some says it's not really faster or better handling (to use the same example). Knowing it has 4 times more horsepower, rear wheel drive, low center of gravity, it a lot easier to make up your own mind!



#9 Don W

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Posted 14 February 2020 - 03:24 PM

It would  help if you told us what your goal is with a mount. For visual use, either is fine but the CGEM II will handle a larger OTA. For imaging, the AVX is a lighter grade mount and not really great for imaging. The biggest differences are in the size and quality. The AVX is inferior in nearly all respects.

 

The CGEM is bigger and uses more precise parts.



#10 bobzeq25

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Posted 14 February 2020 - 04:57 PM

Yeah but in many threads, some says it's not really faster or better handling (to use the same example). Knowing it has 4 times more horsepower, rear wheel drive, low center of gravity, it a lot easier to make up your own mind!

So?  Read the whole post.  It puts you in the picture.  Note that it was given thumbs up by EFT.  His business is telescope mounts; selling, fixing, tuning.  His website:

 

https://www.deepspaceproducts.com/

 

You could research the details yourself.  It won't be all that easy, nothing in astrophotography is.  <smile>


Edited by bobzeq25, 14 February 2020 - 04:59 PM.


#11 Ziguy

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Posted 14 February 2020 - 07:10 PM

I'm simply looking for the technical differences between the 2 mount. Like "the AVX only uses a simple bushing on DEC, the CGEM II uses an actual bearing.".



#12 bobzeq25

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Posted 14 February 2020 - 07:24 PM

I'm simply looking for the technical differences between the 2 mount. Like "the AVX only uses a simple bushing on DEC, the CGEM II uses an actual bearing.".

It's unlikely anyone here (with the _possible_ exception of EFT) can answer you off the top of their head.  When I want to compare gears, etc. for mounts, I research the issue.  For iOptron mounts, the info is available on their website, they have _very_ detailed specs for their mounts.  Ditto most high end mounts.  I simply don't know about Celestron.


Edited by bobzeq25, 14 February 2020 - 07:26 PM.


#13 tonyt

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Posted 14 February 2020 - 08:50 PM

An Australian retailer (andrewscom.com.au) has posted on their website that "an upgraded Advanced VX will be available soon". Perhaps Celestron might finally put a ball bearing on the Dec axis or maybe it will be a smaller version of the CGX?

 

If I was buying an AVX in the US I'd get the tuned version from OC Telescope.

 

The CGEM is a very heavy beast, about 6 or 7 pounds heavier than the Skywatcher AZ-EQ6.



#14 starryhtx

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Posted 14 February 2020 - 10:51 PM

I'm simply looking for the technical differences between the 2 mount. Like "the AVX only uses a simple bushing on DEC, the CGEM II uses an actual bearing.".

Can I recommend a Losmandy G8 over a CGEM? The losmandy seems to me to be of way better quality. About the same price as a CGX.


Edited by starryhtx, 14 February 2020 - 10:53 PM.

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#15 Ziguy

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Posted 14 February 2020 - 11:17 PM

Can I recommend a Losmandy G8 over a CGEM? The losmandy seems to me to be of way better quality. About the same price as a CGX.

Seems like a nice piece of equipment. I definitely check it more in detail.



#16 Ziguy

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Posted 14 February 2020 - 11:18 PM

I found this interesting article Comparing Telescope Drive Technologie


Edited by Ziguy, 14 February 2020 - 11:19 PM.


#17 Michael Covington

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Posted 15 February 2020 - 12:54 AM

The AVX and CGEM have the same hand controller and very similar software; almost everything mechanical is different.  The biggest difference is that the AVX is quite stiff in declination due to the use of a bushing rather than a bearing.  This can make it very difficult to autoguide in declination.   As supplied, it is also somewhat stiff in RA, but the Orange County Telescope bearing upgrade cures that.  

Other mechanical details:  The AVX has a 10-minute worm period (if I recall correctly) and uses integer gear ratios to make PEC more effective.  The CGEM has an 8-minute worm gear period and has some gear ratios that cause PEC to be slightly less effective because some of the irregularities recur at intervals longer than the worm period.

Compared to other brands of mounts, one thing the CGEM and AVX have in common is relatively large backlash (120 arc-seconds on each axis is considered acceptable).  This causes some autoguiders to have trouble calibrating (initializing).

 

I use my AVX for situations that don't require autoguiding, such as 1-minute subs with a small refractor, and longer subs with a telephoto lens.  It is delightfully lightweight and portable.  It does autoguide acceptably with small, lightweight telescopes (e.g., 65-mm refractor), but not as well as the CGEM.   With trained PEC, it has low periodic error, especially after the Orange County bearing upgrade.  I use my CGEM for anything that requires autoguiding.  

 

It is a great convenience that they use the same hand box (in fact, although I have a hand box for each, I usually carry just one of them in my accessory case, and use it with whichever mount) and the operating procedures are identical.

 

I am thinking of replacing the CGEM with an iOptron or Losmandy product, not sure which one.  But the convenience of only having to learn one hand box and user interface has been very helpful so far.


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#18 bobzeq25

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Posted 15 February 2020 - 02:03 AM

Can I recommend a Losmandy G8 over a CGEM? The losmandy seems to me to be of way better quality. About the same price as a CGX.

Well, if you're going to go there...

 

The current Losmandy G8G is $2495.  Capacity is 30-40 pounds.  The wheels (the big gears) on RA and DEC are 2.8 inches, 180 teeth.  A picture.

 

http://www.losmandy.com/gm8.html

 

The CEM60 (which I own) has a capacity of 60 pounds.  The wheels are 5.7 inches, 288 teeth.  It's $2200.  Picture.

 

https://www.ioptron....duct-p/7200.htm

 

The Losmandy is much prettier, the cases are CNC machined and anodized, the CEM60 cases are painted castings.  This has no bearing on function, and painted castings save a lot of money.  The pictures make it dead obvious that the CEM is much sturdier, the wheel size is reflective of shaft size, etc.

 

Losmandy's are nice mounts.  They are also expensive for what you get.

 

http://www.losmandy....untcompare.html

 

If the 27 pound weight of the CEM60 is a deterrent (the weight/capacity ratio is one of the very best), the $2000 CEM40 is lighter than the GM8G (16 pounds), and has the same capacity. Wheels are 4.3 inches, 216 teeth.  The main cases are CNC machined and anodized.   Almost certainly marketing, the CEM60 was criticized for its appearance.  It makes the mount a bit more expensive.

 

iOptron has the light weight thing covered with the CEM mounts.  They were one of the first (maybe the first) inexpensive mounts to come with spring loaded worms, which Losmandy recently adopted.

 

In contrast the CGEMII is 40 (!) pounds.  To a certain extent it means stability.  To a certain extent it means unsophisticated design has been addressed by making the thing _really_ heavy.  The wheel size is 3.5 inches.  If a heavy mount is OK, the 38 pound EQ6-R is the bargain choice at $1650.  Quiet belt drive, the CGEMII has spur gears.

 

"The worms, ring gears, bearings and a variety of structural components in the CGEM/DX/II, Atlas, EQ6, EQ6-R are identical."

 

https://www.cloudyni...r/#entry8507169

 

Lots of good choices out there.
 


Edited by bobzeq25, 15 February 2020 - 09:40 AM.

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#19 WadeH237

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Posted 15 February 2020 - 10:51 AM

Yeah but in many threads, some says it's not really faster or better handling (to use the same example). Knowing it has 4 times more horsepower, rear wheel drive, low center of gravity, it a lot easier to make up your own mind!

To continue the car analogy, you are not asking for the differences in horsepower, drive wheels, and center of gravity.  You are asking about all of the differences.  Obviously, in the case of these two cars, the answer would fill an entire bookshelf.

 

If you could narrow down your question to a few specific aspects that you are interested in, we could probably answer them for you.

 

Also, it would help if you tell us why you are asking.  If you are looking to purchase a mount for visual use, we could compare them.  If you are looking for a mount for imaging, we could compare them.  If you are looking for a grab-and-go mount, we could compare them.  If you are looking to strip off Celestron's motors and controller electronics, we might even be able to help point to some resources.



#20 BobW55

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Posted 15 February 2020 - 11:30 AM

I would only add, PAY THE MONEY, get a Great mount once.

I have the CEM60, yes it was very expensive on my budget, but worth every penny I spent on it.

I have a 102mm refractor I use for imaging with it, and a  8"SCT i use on it for imaging.

I Am in the process of acquiring a AVX mount to use for visual withthe 8".   I might use the AVX for planetary imaging down the road.

 

Like others have said.  The CEM60 is like a Hummer, the AVX is like a Volkswagen Beetle.



#21 Ziguy

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Posted 15 February 2020 - 03:41 PM

To continue the car analogy, you are not asking for the differences in horsepower, drive wheels, and center of gravity.  You are asking about all of the differences.  Obviously, in the case of these two cars, the answer would fill an entire bookshelf.

I never asked for all the differences. 

 

I don't think my question was too general or too much out of context. I mean bobzeq25 brought one difference and Michael Covington brought some more. The sad part is that I'm sure you could could have brought some more. :-)


Edited by Ziguy, 15 February 2020 - 03:44 PM.


#22 orlyandico

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Posted 16 February 2020 - 07:52 AM

The CGEM II has larger worm wheels, can carry more weight, has a bearing in declination, but otherwise is just about the same precision as the AVX.

 

You would use a CGEM II if your telescope is too heavy for an AVX to carry, bearing in mind the 50% rule.

 

There is no need to over-analyze the difference between these two mounts. To use a car analogy, one is a Civic and one is an Accord. They are entry-level China-made mounts, except one has more capacity and slightly better/beefier internals than the other.


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#23 Michael Covington

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Posted 16 February 2020 - 09:09 AM

We should add that there is very little difference between CGEM and CGEM II.  I'm not sure what the difference is.

Orthogonal to this, newer hand boxes have a USB serial port built into them (so you can plug in a USB cable and your computer will see it as a serial port).  Older hand boxes have a serial port.  This is true of both the CGEM and the AVX.



#24 aa6ww

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Posted 16 February 2020 - 12:39 PM

  I may have read recently that the AVX and CGEMII both use the same motors now. 

 

Also the bigger and better CGEMII is only better if you need the extra weight capacity of the larger mount. For scopes like my C8, my SW-120, the Avx is a better choice for me. Moving a 40 pound equatorial head for a small OTA isn't better for me in anyway. For my C11 and 6" APO, the CGEMII is a better choice for me.

 

A Civic would be a better choice for me, taking my gear to a dark site or taking someone else with me when I went out to that darker site. Bigger, Faster, or "more" by no means, always instantly means better, YMMV.

 

....Ralph 

 

 

 

The following is for traditional imaging only, visual or EAA is a _completely_ different ballgame.

 

I don't know the details, but typically the differences between a $900 mount and a $1650 mount involve (rough order of importance):

 

Better, bigger bearings.  Bigger more precisely made gears.  Bigger shafts.  Bigger motors (a cheap part of the mount, manufacturers have been known to use the same motor in different mounts for simplicity).  Better electronics.  A sturdier case to hold everything rigidly.

 

Price is an excellent guide to mount quality.  There simply is _no_ comparison between these two mounts if you're planning on doing traditional imaging.  One costs almost twice as much as the other.  The AVX is not some mystical bargain, it's a very inexpensive mount, perhaps the least expensive that's somewhat suitable for traditional imaging with a telescope.  Depending on the specific example you get, it may be suitable for a small refractor for imaging.  Some find it so, some not.

 

You don't actually need to know details to know that a $50,000 Corvette is _way_ faster and better handling than a $20,000 Civic.  This is similar.


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#25 Michael Covington

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Posted 17 February 2020 - 01:12 PM

I would only add, PAY THE MONEY, get a Great mount once.

I have the CEM60, yes it was very expensive on my budget, but worth every penny I spent on it.

I have a 102mm refractor I use for imaging with it, and a  8"SCT i use on it for imaging.

I Am in the process of acquiring a AVX mount to use for visual withthe 8".   I might use the AVX for planetary imaging down the road.

 

Like others have said.  The CEM60 is like a Hummer, the AVX is like a Volkswagen Beetle.

The question is where the CGEM fits on that scale.  Would CGEM to CEM60 (CEM40 etc.) be a substantial upgrade?  Or are they comparable?




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