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EXOS2-GT PMC-Eight vs EQ6-R

astrophotography equipment mount
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#1 zernikepolynomial

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Posted 30 June 2020 - 08:32 PM

Both have 20 pound payloads with active guiding.

 

The new underdog vs the older chunky boy. One has a simplified belt drive with the PMC-Eight system, the other has a more complex belt drive with the older SynScan.

 

The new exos2-gt has a maximum visual payload of 40 lbs, with a maximum astrophotography payload of 28 lbs.

 

The eq6-r has a maximum payload of 44 lbs.

 

The eq6-r is twice the price, but is it twice the quality? You decide.



#2 bobzeq25

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Posted 30 June 2020 - 09:18 PM

Twice the quality?  No.  More quality?  Definitely.  The bearings and gears are larger and more precise.  Etc.

 

The EQ6-R is too heavy for me.  But it's a fine mount.

 

As with most equipment choices, just a personal choice.  For longer focal lengths I'd definitely prefer the EQ6-R.  The EXOS is not some magic bargain.

 

Not so minor point.  One shouldn't make too much of manufacturers weight ratings.  They're whatever the manufacturer wants to claim, there are no standards.


Edited by bobzeq25, 30 June 2020 - 09:19 PM.

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#3 zernikepolynomial

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Posted 01 July 2020 - 12:00 AM

Twice the quality?  No.  More quality?  Definitely.  The bearings and gears are larger and more precise.  Etc.

 

The EQ6-R is too heavy for me.  But it's a fine mount.

 

As with most equipment choices, just a personal choice.  For longer focal lengths I'd definitely prefer the EQ6-R.  The EXOS is not some magic bargain.

 

Not so minor point.  One shouldn't make too much of manufacturers weight ratings.  They're whatever the manufacturer wants to claim, there are no standards.

What kind of results were you getting for guiding with the exos2 pmc-eight?



#4 bobzeq25

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Posted 01 July 2020 - 12:58 AM

What kind of results were you getting for guiding with the exos2 pmc-eight?

I don't have either mount.  I have read a great deal about them here.  And I know this.  Mount quality is strongly correlated with price.  The good news about mounts is that you generally get what you pay for.  The bad news about mounts is that you generally get what you pay for.  <smile>

 

The EQ6-R is not heavy because they added lead weights.  <grin>  It's heavy because the mechanical bits are sturdier.  It's not more expensive because they decided to charge more, the market is quite price sensitive.  It's more expensive because it's manufactured to a higher specification.

 

There is no magic here.  In addition to price and weight, look at the two mounts.  The EQ6-R clearly has larger mechanical pieces like gears and bearings.  It counts.

 

As I said, the EQ6-R is not twice as good as the EXOS.  And the EXOS is not as good as the EQ6-R.  People don't buy the EQ6-R because they're ignorant.


Edited by bobzeq25, 01 July 2020 - 01:06 AM.


#5 EFT

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Posted 01 July 2020 - 01:30 AM

Twice the quality?  No.  More quality?  Definitely.  The bearings and gears are larger and more precise.  Etc.

Yep.  The EXOS is just a CG5 with a different drive system.  The EQ6-R is the next weight (capacity and physical) class up from the EXOS.  There is no real comparison.


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#6 zernikepolynomial

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Posted 01 July 2020 - 02:04 AM

I don't have either mount.  I have read a great deal about them here.  And I know this.  Mount quality is strongly correlated with price.  The good news about mounts is that you generally get what you pay for.  The bad news about mounts is that you generally get what you pay for.  <smile>

 

The EQ6-R is not heavy because they added lead weights.  <grin>  It's heavy because the mechanical bits are sturdier.  It's not more expensive because they decided to charge more, the market is quite price sensitive.  It's more expensive because it's manufactured to a higher specification.

 

There is no magic here.  In addition to price and weight, look at the two mounts.  The EQ6-R clearly has larger mechanical pieces like gears and bearings.  It counts.

 

As I said, the EQ6-R is not twice as good as the EXOS.  And the EXOS is not as good as the EQ6-R.  People don't buy the EQ6-R because they're ignorant.

So what is different about the bits in the eq6-r than the exos2? Is there some specification that the worm gears differ in?



#7 zernikepolynomial

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Posted 01 July 2020 - 02:06 AM

Yep.  The EXOS is just a CG5 with a different drive system.  The EQ6-R is the next weight (capacity and physical) class up from the EXOS.  There is no real comparison.

I mean the drive system is a pretty big deal, can you explain specifically why there is no real comparison?



#8 EFT

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Posted 01 July 2020 - 03:06 AM

The drive system is not a big deal at all.  Between the CG5 and the EXOS2, it is a stepper vs. servo motor difference but the worms and ring gears are essentially the same and of fairly low precision.  From there it doesn't really matter much what motors are used or whether or not the worm is spur gear or belt driven.  

 

We don't have exact specifications for the precision of the worms and ring gears, but the ring gears in the EQ6-R are much larger and thicker, made with brass instead of aluminum, and are clearly cut better.  The worm is the EQ6-R is stainless steel instead of brass, are twice the diameter, and cut at least as well, if not better.

 

The belt drive in the EQ6-R is similar but has a much greater pulley to pulley distance.  

 

I can't tell you for sure whether or not the EXOS2 has bearings on the worms, but it is fairly likely they do since the CG5 and AVX mounts do.  The bearings are much smaller than those of the EQ6-R.  However, some interior photos that I have seen suggest that the mount may be more similar to the LXD55/75 mounts which did not have worm bearings.

 

The EQ6-R axes are steel and supported by a ball bearing on one end and a taper roller bearing on the other.  The RA axis of the EXOS2 is going to be a cast aluminum cylinder that is part of the entire RA axis shaft and head assembly which is supported by one ball bearing on one end and a sleeve bearing (i.e., somewhat smooth metal on metal) on the other.  There is a thrust bearing on the end of the RA but it has nothing to do with the centering and support of the axis.  The DEC axis is of the same construction as the RA only it doesn't have any ball or taper bearings on the shaft and instead relies on sleeve bearings and plastic bearings/spacers.  The EQ6-R ring gears ride on two ball bearings the same size as the axis bearing.  The EXOS2 ring gears simply ride on metal surfaces with no bearings.

 

The current Synscan control system is a progression of a system that has been in use for many years and is reasonably solid and dependable.  EXOS2 PMC-Eight GoTo System doesn't appear to be in very wide spread use at this time.

 

I could probably go on for much longer, but when it comes down to it, these are two different classes of mount with the EQ6-R being by far the better of the two.  For light-weight, short focal length imaging, the EXOS2 might work just fine for someone and the performance with the same optical/imaging system on the EQ6-R might not be noticeable.  But as soon as it comes to increasing the instrument load, the focal length, and/or the exposure times, the difference is substantial regardless of the stated capacities.  Larger gears, larger bearings, more bearings, heavier mount, and better overall design make a very big difference and account for the difference in price.


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#9 Devonshire

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Posted 01 July 2020 - 11:08 AM

To me, this is Apples and Oranges...

 

I don't have an eq6-r, but I did look at them when I was making my purchase decision, as they are often recommended here.  I required portability, and the eq6-r was itself heavier than I wanted to lug about, and its payload capacity was far larger than anything I wanted to hoist up on it.  So there's that.  For a quality comparison to be relevant, you'd need to determine whether the eq6-r would even make it to your short list on that basis (or, for that matter, budget).

 

The iOptrons were closer in portability for me, and I looked at them as well. 

 

I ended up with an EXOS2 PMC8.  If you try to judge the mount by its unguided performance, you'll end up pretty much validating what's said above about mechanics and price.  Mechanically, it's an LXD75 with ball bearings on both axes and the worms.  Lots of people seem to have liked the LXD75's back in the day, but it is what it is. 

 

But this mount guides well.  What's different is the power train and the controller.  Where does periodic error come from?  Rotating components.  What's rotating?  Not much - a small pulley on the motor,  a large pulley on the worm shaft, and of course, the axis itself.  That's it.  Not even an idler on the belt.  Take care with your mechanical adjustments and PECprep will show you a fairly smooth periodic error that's pretty easy to guide around.  And you don't have to guess about those adjustments - after I figured out what was needed, I wrote up a short tuning doc and published it on the PMC8 support forum.  

 

Then there's the PMC8 controller - part of what sold me.  I quizzed Jerry a lot on that, pre-purchase.  I'm a retired IT architect, and because it was so different, I wanted to understand.  When I finally understood his design, and for that matter, the chip he based it on, my eyebrows went up.  Only somebody with a real eye for reliability would have made the choices he did. 

 

And the PMC8 is control-program agnostic.  ASCOM, INDI, ES's own (Visual) 'Explorestars', and if something else comes along later, just write a driver that speaks the PMC8's well-documented control language, and you're good to go.  People control them with all sorts of programs, so no, it's not a toaster and you do have to think through what you want, but if you value flexibility, it's there.

 

I'm careful with my guide ratio, balance, and adjustments and I typically am able to guide 180s, 300s, or 600s exposures, at 621mm or w/reducer, depending on target and conditions, with round stars.  Talk about price vs quality all you like - if you are prepared to give this mount what it needs - and I think you do need to do that - it can punch well above its price point.

 

HTH...


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#10 ChrisMoses

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Posted Yesterday, 07:18 AM

You should head over to the PMC-8 user group on groups.io and post your question.  There are a lot of very knowledgeable Exos-2 users.  Jerry, the mount designer is on the forums every day.  He should be able to tell you the exact Exos-2 technical specs.  You can also see real world pics of how much people are loading it up.

 

Don;t forget other important issues, such as customer support  and a large, vibrant user community.  Explore  Scientific really excels in those areas.

 

Chris Moses


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#11 Dhellis59

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Posted Yesterday, 09:42 AM

Hi,

 

 

As a current exos2pmc8 owner, and a former owner of two other mounts;  one less capable and the other a supposedly more capable, twice as heavy and costlier mount, I can say the exos2pmc8 is a very good bang for the buck mount regardless of it's origins.

 

Having not owned an SW eq6, I won't make the claim that the exos2 is as good or anything like that. I will say the pmc8 is a very intriguing step forward in the use and implementation of technology in the industry though.

 

However, I think the customer service is outstanding. The folks at ES are very attentive to ensuring their customers get all the support they need to properly use their products. 

 

 

Clear skies, 

 

Darryl


Edited by Dhellis59, Yesterday, 11:29 PM.

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#12 Don-richardo

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Posted Yesterday, 10:16 AM

I did a lot of net surfing looking at the exos2. And it seemed to be hit or miss for reliability. No experience with the other mount but i would look to how long it's been out. As one factor in my assessment. The exos2 gt is probably a good mount. the issues seemed to be around the controll
system more than anything else. The only bad thing i've heard about the EQ6-R is thats it's heavy lol. Not a bad thing at that payload rating IMHO.

#13 PatrickVt

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Posted Yesterday, 10:42 AM

I did a lot of net surfing looking at the exos2. And it seemed to be hit or miss for reliability. No experience with the other mount but i would look to how long it's been out. As one factor in my assessment. The exos2 gt is probably a good mount. the issues seemed to be around the controll
system more than anything else. The only bad thing i've heard about the EQ6-R is thats it's heavy lol. Not a bad thing at that payload rating IMHO.

There is a LOT of confusion about the reliability of the EXOS2 and this is because there are two versions of the EXOS2. 

 

The older version is the mount that had garnered a lot of bad ink and bad word of mouth regarding reliability, usability and accuracy.  And, honestly, those complaints are definitely valid and deserved.  That older mount was actually a Bresser mount in an adapted Meade LXD75 mount.  Then, Explore Scientific briefly sold a rebranded version also called the EXOS2-GT but it really was an all-Bresser EXOS2, just rebranded as Explore Scientific.  Even though some retailers may still have some stock of these older mounts, I believe Explore Scientific has discontinued this original EXOS2-GT.    

 

Explore Scientific did the right thing in once again adapting this mount completely while changing the name to EXOS2-GT PMC-8.  This version of the mount has very little in common with the original EXOS2-GT.  The PMC-8 version is light-years ahead of the original version.  It is accurate.  It is reliable.  It is very usable in every aspect.  And, more importantly, it is nothing like the original EXOS2-GT.  Additionally, as others have noted, the Explore Scientific customer service is second to none which is the complete opposite of what we hear about many other astro manufacturers.

 

I truly wish the name had been changed more significantly because I believe this is where all the confusion originates.  The new PMC-8 version is getting a lot of undeserved and unwarranted bad mouthing.   

 

Patrick


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#14 zernikepolynomial

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Posted Yesterday, 02:48 PM


The EQ6-R axes are steel and supported by a ball bearing on one end and a taper roller bearing on the other.  The RA axis of the EXOS2 is going to be a cast aluminum cylinder that is part of the entire RA axis shaft and head assembly which is supported by one ball bearing on one end and a sleeve bearing (i.e., somewhat smooth metal on metal) on the other.  There is a thrust bearing on the end of the RA but it has nothing to do with the centering and support of the axis.  The DEC axis is of the same construction as the RA only it doesn't have any ball or taper bearings on the shaft and instead relies on sleeve bearings and plastic bearings/spacers.  The EQ6-R ring gears ride on two ball bearings the same size as the axis bearing.  The EXOS2 ring gears simply ride on metal surfaces with no bearings.

 

Maybe I am misunderstanding you, but the one thing I do remember reading about the latest exos2 is that it has ball bearings in both axes. So the DEC axis, at least according to them, is using a ball bearing on the shaft.

 

As for the drive system, I guess I simply disagree on it not being a big deal. The drive system is the bottleneck that determines how responsive a system will be to transmitted torque. So in the case of guiding, it is the primary bottleneck to keep RMS down. But in the case of no guiding, we are only transmitting large torque at the very beginning of tracking, and your argument definitely applies more to keep consistent RMS.

It would seem unguided, the eq6-r would destroy the exos2.



#15 Devonshire

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Posted Yesterday, 03:08 PM

Mr. Thomas,

 

Incorrect.  There are ball bearings on each end, of each axis, whether DEC, RA, or the Worms, just as ES says. 

 

I've had mine apart, and took a few pictures along the way.  Here's a shot of the DEC axis, showing the bearings.

 

 

IMG_0891a.jpg


Edited by Devonshire, Yesterday, 03:10 PM.

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#16 EFT

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Posted Yesterday, 06:01 PM

You are correct.  I was forgetting that the Explore Scientific products were not being made by Synta which meant that they were re-ups of the LXD75 mount, not the CG5.  The LXD75 (unlike the LXD55) had two ball bearings on each axis (a benefit over the CG5) but no worm bearings.  Do you have a picture showing worm bearings in the EXOS?  Those are far more important than the shaft bearings and would be an upgrade that this particular mount design has always needed.

 

In regard to the drive, both motor types have advantages and disadvantages.  There's a good explanation here:   In this application it comes down largely to the accuracy and torque of the two motor types although there are other important differences depending on application and implementation.  In my opinion, the greater accuracy of the servo motor is more important than the low speed torque of the stepper motor.  I can live with a longer ramp-up time when beginning to move more than I can live with decreased accuracy (and yes, that means even with microstepping).  That's one reason why the Celestron servo-driven mounts are known for their pointing accuracy and as long as the motor gearbox is specified correctly, they also have sufficient torque to move a slow speeds for the purpose of guiding commands.  On the average performance level of these mounts, a stepper motor with an encoder could be an improvement, but the stepper motors are always limited by their minimum step resolution and the encoder adds cost to what is generally a simple and fairly inexpensive motor.  Overall, it ends up mostly being a wash which is why Synta uses both types of motors in its mounts that are otherwise identical when it comes to the rest of the drive system.  It's also why at least some premium mounts use AC servos which are more accurate and durable than DC servos.

 

In a perfect world where the production was top notch and the QA/QC were very good, an EQ6-R would probably do better unguided than the EXOS but primarily because of the size of the worm and ring gears and the better design and better materials used in their manufacture.  It's not because of the motors used.  That's why the comparison of the EXOS with the EQ6-R is not a valid comparison.  A comparison to the AVX and the SkyView Pro would be much more realistic.  If you add a servo mount to the list like the the CGEM, it would likely beat the other two but still not by a lot in this situation.  The CGEM and the EQ6-R use the exact same ring gears and worms (with a slight difference in worm shaft due to the EQ6-R belt drive) which are the most important parts of the drive system.  However, with QA/QC being far from ideal, the variation in all these mounts largely negates their difference on average.



#17 bobzeq25

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Posted Yesterday, 07:27 PM


As for the drive system, I guess I simply disagree on it not being a big deal. The drive system is the bottleneck that determines how responsive a system will be to transmitted torque. So in the case of guiding, it is the primary bottleneck to keep RMS down.

No.  The primary bottleneck is your seeing.  My CEM60 guides at 0.5 arc sec RMS, on unusually steady nights.   0.7 - 0.8 is more usual.  It can go above 1.0, but then the night is so unsteady that imaging is not very worthwhile.

 

The next bottleneck is the size and quality of the gears.  Size is important, because it averages out gear errors better.  Stepper versus servo is really not an issue, people make fine mounts with both.

 

The thing to understand about guiding is that it's worthwhile, but _very_ far from perfect.  There are things that affect the guidestar that are just noise (like seeing), and things (like periodic error) that are signal.   The signal to noise ratio is horrible, maybe less than 1.  The saving grace is that the noise is generally high frequency, the signal low frequency.  PhD2 is largely a collection of low pass filters that you tune to work well with each other.  It's an art.

 

Guiding is very much like the bartenders dog playing the piano.  "Bartender, your dog is a lousy piano player."  "The wonder my friend, is not that he plays badly, it's that he plays at all."  <smile>

 

Bottom line.  Guiding is necesary to get the best from any mount.  The EQ6-R would not work well unguided, unless the focal length was unusually short, and the subexposures unusually short.  But guiding will not turn a mediocre mount into a good one.  The less you have to guide, the better.
 


Edited by bobzeq25, Today, 12:01 AM.


#18 Devonshire

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Posted Yesterday, 08:33 PM

Mr. Thomas,

 

No, I don't have a useful picture of the worm bearings.  There's not much to see.  They're buried in the worm block, with only a small silver ring visible around each shaft end.  But they're there, and with a tension adjustment.

 

But to BobZ's point... if you're doing AP, you will want to guide, so that (and the seeing that limits it) is really the yardstick.  Not much point in focusing on unguided performance - took me a while to learn that, but once I did, I didn't look back...


Edited by Devonshire, Yesterday, 08:34 PM.

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#19 EFT

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Posted Today, 12:00 AM

I hope that there are ball bearings on the worms but I have to see them.  There is a long history of this particular design having no bearings at all on the worms and a high possibility that there are shims or sleeves.  Bearings should be pretty obvious.  The following photos show a worm bearing in a similar housing from the "tension adjustment" (which they would have whether or not there are bearings) end, from the opposite end of the worm, and from the inside of the housing (yellow in this case because of the sealed bearings that I use).  They are difficult to make out in the adjustment end but fairly obvious in the other two.  Essentially, the bearing with be a fair bit larger in diameter than the worm shaft so that from the inside you should be able to see the outer race and some of the shield.  From the side opposite the adjustment mechanism, there will either be no space between the worm shaft and housing (no bearing), a brass or silver ring around the worm (a bushing), or the inner race and part of the shield visible.   

 

 Worm_Bearings_1.jpg

 

Worm_Bearings_2.jpg

 

Worm_Bearings_3.jpg


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#20 Devonshire

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Posted Today, 09:58 AM

Mr. Thomas,

 

What an astonishing thing to say!  I've seen the bearings and that will have to do.  Or, I suppose, you could call ES...

 

In the meantime, I think I've done as much as I can to help with the OP's questions, and it's time for me to check out of this thread.



#21 wcblack

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Posted Today, 10:54 AM

I have an EXOSII-PMC8 that I purchased in October 2019 and I can confirm ball bearings on the worm gears.

I also have an LXD75 from years ago. The overall design of the two mounts is essentially the same, but the additional bearings in the EXOSII make all the difference for smoother performance and I love the PMC8 control system. The old LXD75 had brass bushings on the worm gears. I've had both mounts apart and the bearing upgrades are apparent.

 

I do EAA type astrophotography (not a lot of post-processing) and the EXOSII works great for me. I have 27 lbs of equipment on the mount with 27 lbs of counterweight and can guide to 0.5" RMS if the seeing is good. The seeing is always my limiting factor.


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#22 tmyers

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Posted Today, 11:11 AM

I have also seen the bearings on the worm blocks as I removed them to tune and reapply grease. I didn't take pictures as I didn't think at the time I would have to prove what I saw.

I looked at the EQ6 before buying the EXOS2-GT, with PMC8. I have found the PMC-8 control system to be a definite move in the right direction over a handheld device. While the wireless control works well with a tablet/phone, I really wanted the wired connection to my laptop and the PMC-8 makes that very easy.

Since I have never have owned an EQ6, the only real comparison I can make is that the EXOS2 does what I need it to do for less than half of the cost. Some say you get what you paid for, and I can say that I got a lot for what I paid for with my EXOS2.

 

Someone mentioned Customer Service, and that is where ES really shines in my opinion. But the importance is that the customer service I am referring to is not because of problems with the mount. Most of what I see is help for noobs like me trying to figure things out. They are patient beyond belief, they truely love what they do and it shows.

 

I have no doubts that the EQ6 is a good and even great mount, but so it the EXPS2-GT with PMC8 control.


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#23 EFT

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Posted Today, 12:34 PM

I have an EXOSII-PMC8 that I purchased in October 2019 and I can confirm ball bearings on the worm gears.

I also have an LXD75 from years ago. The overall design of the two mounts is essentially the same, but the additional bearings in the EXOSII make all the difference for smoother performance and I love the PMC8 control system. The old LXD75 had brass bushings on the worm gears. I've had both mounts apart and the bearing upgrades are apparent.

 

I do EAA type astrophotography (not a lot of post-processing) and the EXOSII works great for me. I have 27 lbs of equipment on the mount with 27 lbs of counterweight and can guide to 0.5" RMS if the seeing is good. The seeing is always my limiting factor.

This is good news then.  This is a significant improvement to the old mount since it was a real shortcoming.  Along with the axis bearings, this should technically be a better mount than the AVX mechanically.  I'm sorry that I couldn't just take the word of one person who could prove one thing with photos but not another thing nor have I seen anything were ES said anything about the mount's bearings.  I've had a lot of experience with this basic design and I've seen people misidentify things like this before.  These companies tend to be very hard pressed to make significant changes sometimes, even when they have an opportunity during a redesign.  The CG5 to AVX is an excellent example where they could have added ball bearings to the DEC axis but didn't.  The worm bearings always made the CG5/AVX a better mount overall than the LXD mounts but the DEC axis bearings where/are where they always fell behind mechanically.


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