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Stupid CGEM vs. CGEM DX question

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#1 dr.who

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Posted 06 November 2013 - 02:37 PM

Please pardon my stupid question here but I couldn't find the answer with my Google-Fu...

I am fascinated by the whole CGEM and CGEM DX lineup but can't seem to find the compelling reason for the DX over the CGEM based on the differences. Those differences being the larger counter weight bar, some kind of "bell" to allow heavier objects on the tripod, and bigger tripod. All internal components are the same. It reads to me like the weak link in the configuration is the tripod...

If I were to put the CGEM on a pier like the AP 6" Eagle or Parallax would the payload capacity go up to the level of the DX or does that 1 1/4" weight bar and "bell" make that much difference? As in a $500 difference in price?

Thank you in advance for taking the time to answer this stupid question.

#2 dragonslayer1

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Posted 06 November 2013 - 02:57 PM

Hey Don,
I asked that question in Team Celestron, was about motors and electronics etc and this is the answer I got
""It used to be that the CGEM and the CGEM had different electronics. But as of some time last year, all CGEM's have the updated electronics. So nowadays, the biggest differences is the Tripod, and the longer clutch knobs.""
Kasey

#3 dr.who

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Posted 06 November 2013 - 03:00 PM

Cheers mate. That's what I ran into as well. But I am not enough of a Mechanical Engineer to know if that bigger weight bar and bell make that much difference...

#4 De Lorme

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Posted 06 November 2013 - 03:05 PM

This answer isn't relative to you but maybe to someone else.
Being visual only I have my CGEM tripod at 49"{50" total} and I have no problems; . Before I moved it to this height it hit the tripod once but I may have bumped it. If I do bump the tube it only takes a second to dampen down. After thinking about buying a Atlas Pier adaptor I decided it just wasn't necessary. With the tripod at this height I
no longer have a problem looking straight up.
De Lorme

#5 dmdouglass

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Posted 06 November 2013 - 03:31 PM

Your question:
"If I were to put the CGEM on a pier like the AP 6" Eagle or Parallax would the payload capacity go up to the level of the DX or does that 1 1/4" weight bar and "bell" make that much difference? As in a $500 difference in price? "

The (My) answer:
Yes !

I asked that same series of questions of Celestron Engineering. One area to consider is the amount of "counter weight" you will be needing. They do feel that for heavier counter-weight loads, you should have the heavier bar and attachment of the bar to the mount.

I have two of their 17lb counterweights (34lbs) , with the standard CGEM, pier mounted, with about a 30 lb operational payload. All works very well. Primary usage is imaging, and 3-5 min subs are my norm. 8" Edge(HD), 80mm Meade EDAPO, and two cameras with the main camera an SBig.

Configuration can be seen here:
http://www.az-dahut.net

#6 dr.who

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Posted 06 November 2013 - 04:04 PM

Cheers guys. I really only need/want the CGEM for the Edge 1100. The AVX handles it fine but I figure the CGEM would handle it better. And I would like to put my Tak in tandem as well for outreach and I can't do that with the AVX...

Thank you David. That is a nice rig!

#7 orlyandico

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Posted 06 November 2013 - 10:37 PM

it boggles the mind that one would put a CGEM on an AP Eagle pier...

that said, back when I had a CGEM, I gave some thought to having a 1.125" counterweight bar machined for it, that way I could use AP weights on it (since I have 2 AP mounts with the - small - 1.125" CW shaft).

The standard CGEM bar is 20mm, same as the AVX and slightly better than the old Atlas "spaghetti counterweight bar".

#8 dr.who

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Posted 07 November 2013 - 12:59 AM

:lol: Hi Orly! :waytogo: right there with you! What with said pier being close to the price of the CGEM. But it was as an example not an actual practical application. I am trying to wrap my head around the mechanics of it vs. the marketing part.

I understand the rigidity of the larger bar and that the heavier tripod will dampen vibration better but with the removal of the tripod from the equation is the bar on the CGEM such rubbish that it would prevent the mount from handling the extra 10 lbs of weight? It's the same motors bearings PWM module etc...?

#9 orlyandico

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Posted 07 November 2013 - 01:10 AM

The CGEM bar is (probably) OK for up to its rated capacity of 40 lb. I never put more than about 30-35lb on mine (fully loaded C9.25) and the bar didn't seem to be an issue (needed two 17lb weights).

Frankly the CGEM has many other mechanical issues that swamp whatever problems are caused by the CW bar flexing (such as significant backlash in both axes, the 8/3 gearbox error, ad infinitum..)

So.. I don't think the bar will be a factor. I just wanted a 1.125" bar because it would enable me to have only one set of counterweights for everything. Never went that route though, sold the CGEM.

#10 dmdouglass

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Posted 07 November 2013 - 11:41 AM

orlyandico....

We hear you.... we hear you....
Over and over and over and over...

You are getting (at least with me) the reputation of being the "Meade style basher of the CGEM threads..."

You show up on every one of them, and post and post and post until we all want to stop reading the threads. I sure wish you would give it a rest !

#11 crow

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Posted 07 November 2013 - 11:47 AM

The DX has a different spec in the electronics, provides more power to the motors. DX tripod is well built for sure, pretty heavy, about the same weight as the mount head itself.

#12 dr.who

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Posted 07 November 2013 - 11:53 AM

Hey Crow. Thank you for the input. I checked in on that and as it turns out the internals (electronics, motors, gearing, etc) are identical now on both platforms. The only difference is the tripod and weight bar.

Which is what is causing me fits. I can do the math on the effects in terms of vibration (cantilever) from weight load of a 3/4" diameter steel bar of n" of length vs. one of 1 1/4" diameter at the same weight load but it doesn't pencil out as compelling which is what has me tied up. I am either doing the calculations wrong by an order of magnitude or as I said it doesn't pencil out.

#13 orlyandico

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Posted 07 November 2013 - 12:42 PM

David, I am merely opining that any differences in the counterweight shaft diameters (and therefore stiffness) are insignificant compared to the CGEM's other issues. I don't see that as bashing. In any case, feel free to ignore my posts. I believe there is an option to suppress the posts of specific people.

#14 Chuck Hards

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Posted 07 November 2013 - 12:58 PM

I'll be the CGEM poster child.

I love mine. It works well, always has, has an acceptably low amount of backlash. Sets up quickly, works for me from an ergonomic standpoint, is sturdy. The GoTo works every time. Tracks well, periodic error is acceptably small. I typically use it with a side-by-side dual scope setup and don't have any overload problems even with a C-6 on one side and 80mm ED or 100mm ED refractor on the other. Toss a camera and autoguider on there and it's still a gem (see what I did there?).

Add to that the fact that I got it on sale a few years ago, and I'm completely satisfied in what I got for the money.

I've always leaned toward slightly more counterweight closer to the CG, than less weight further out on the shaft. Seems to help lessen any vibration- of which I detect none on my setup. With the standard CW bar.

YMMV.

#15 crow

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Posted 07 November 2013 - 02:39 PM

That makes sense, i'm running on info obtained when i had mine.

The more robust CW bar helps, what i found was while they supplied with me with two CW's I only needed one to balance the 1100 Edge. Is that the case with the standard bar? No big deal but its one less weight to carry.

I was actually sad to let mine go, it impressed me more, the more i used it, if you know what I mean. I let it go simply due to weight, I like to be mobile, the DX is heavy duty.

#16 Jim Romanski

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Posted 07 November 2013 - 04:03 PM

The tripod for the DX is HUGE and tall and heavy. If you need this for a larger or longer scope then it's a no brainer. But it's quite the beast to haul in and out of the house.

#17 Stew57

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Posted 07 November 2013 - 04:27 PM

Telling the truth is not bashing. Wish someone had told me about the cogging, the 8/3 error and PEC before purchase as I would have gone a different route. I have kept mine and don't have plans to get rid of it, but I have had to change how I had wanted to use it.

#18 WesC

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Posted 07 November 2013 - 04:44 PM

The truth is, not everyone has these problems. And and not everyone is imaging or imaging at long FL.

I use mine for visual only and its a great mount for that. Especially for the extra $100 I paid for it!

PEC, cogging and 8/3... none of that matters a lick for visual use!

#19 Stew57

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Posted 07 November 2013 - 05:15 PM

Exactly right!

#20 dr.who

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Posted 07 November 2013 - 06:45 PM

I've always leaned toward slightly more counterweight closer to the CG, than less weight further out on the shaft. Seems to help lessen any vibration- of which I detect none on my setup. With the standard CW bar.

YMMV.


Actually this makes good sense mechanically since you are shortening the proverbial length of the cantilever thus limiting the potential movement.

#21 ur7x

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Posted 07 November 2013 - 07:10 PM

The DX has a different spec in the electronics, provides more power to the motors. DX tripod is well built for sure, pretty heavy, about the same weight as the mount head itself.


This is no longer the case, if it ever was, Celestron came clean with the motors being the same and the control boards being the same about a year ago. The motors had the same part number, the control boards had different part numbers (albeit very similar) but looked identical. Celestron announced in October of 2012 that the control boards were interchangeable and were the same. So if your mount is newer than that it has guts the same as a DX, if your mount is older than that... it likely has guts the same as DX.

Here is the direct quote from the Celestron Support Knowledge base.

"The two mounts use the same motors, motor boards and the same gear box"

The difference is in the tripod/adapter and the balance shaft and that's all.

#22 dr.who

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Posted 07 November 2013 - 07:32 PM


"The two mounts use the same motors, motor boards and the same gear box"

The difference is in the tripod/adapter and the balance shaft and that's all.


Which still begs the questions of: Why, with the heavy tripod removed, the DX will do 50 lbs and the CGEM will only do 40? And does that 1/4" bigger diameter weight bar make so much difference that it allows for 10 more lbs of payload...?

I guess where I am ultimately headed with this is if I stick a CGEM mount head on a Parallax 8" steel portable pier will the CGEM with it's current weight bar allow me to get 50 lbs of total payload onto it without problem or do I actually need the bigger weight bar?

I say that because in difference to Orly the AP Eagle pier was a bad example to use. I am actually considering a Parallax pier by the way and some day I think I will get a 14" SCT but would also like to know if I actually have to replace the mount too or could use the CGEM...? That 14" would be for visual only by the way. ;)

#23 orlyandico

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Posted 07 November 2013 - 07:46 PM

Dr Who, I wouldn't lose sleep over the counterweight bar.

Weight ratings for this class of mounts aren't very reliable anyway. There's a thread somewhere here on this forum about a guy who put 100 lb on an Atlas - spaghetti 18mm counterweight shaft and all.

So if your intent is to use a Parallax pier going forward, I'd get the regular CGEM and save the bucks. Test it very well to make sure you get one with low 8/3, if you can.

#24 WesC

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Posted 07 November 2013 - 07:48 PM

For visual it should be fine. But, for myself, I would go for the DX as its just that much more solid and taller. The 14 is a BIG scope.

I find the CGEM is plenty solid for visual with my Edge 11. As long as the legs are not extended on the tripod, I can literally lay my face on the eyepiece and it doesn't move, rock solid.

My only issue is that I want to raise the mount higher without extending the legs. I think I'm going to grab the Orion Atlas pier extender so I can do that.

#25 Stew57

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Posted 07 November 2013 - 08:01 PM

I put 45lbs on my CGEM and it is fine. If the internals of the DX can take 50lbs so can the CGEM.

http://s906.photobuc...to CGEM/P106...

http://s906.photobuc...to CGEM/P106...






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