Notes on tuning the EXOS-2/PMC8 mount hardware V2 #EXOS2


 

Folks, I've just installed Version 2 of my EXOS-2 tuning notes in MOUNTS/files.
some minor wording and content updates, plus new content in sections 7.5 and 8
 
Enjoy!  Feedback welcome.
 

- Bob 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Alex Arjomand
 

Awesome :) I haven't read your V2 yet however I found V1 very helpful. Thank you for your hard work!
--
Mounts: ES EXOS2 PMC-8
Scopes: Celestron C8, 10" Antares Dobsonian
Software: ASCOM, Stellarium, SharpCap Pro, ASPS, Ascompad
Computer: Lenovo X1 Carbon, Windows 10/64
Cameras: ZWO ASI385MC
Location: Toronto, Canada (Bortle 8)


Darryl Ellis
 

Outstanding document Robert.  I only meant to scan it while here at work, lol, but found myself going through it in a lot more detail than I had planned. 

Thank you for explaining the heavy east and camera heavy balancing.  For some reason I have had trouble getting my head wrapped around that concept.  However, your explanation made it apparent.

You may recall that at one point I posted that I was getting five minute subs with my Exos 2 using an RC6.  Balance and proper guide scope were the key.  Well I have returned to a modified version of that, but have not yet repeated those results.  This made me start thinking about how I can better balance things and improve the performance of my setup.

Your guide provides the information I need to deep dive into making the necessary improvements.

I really appreciate your work and sharing it with us.  Thank you.

Darryl
--

DHEllis59, Dover, DE

Astro Tech RC 6 w Pegasus Focus Cube and QHY10 OSC Camera
Orion ST 80 Guidescope and QHY 5 III 290c Guide Camera 
Explorer Scientific EXOS GT 2 With PMC Eight Controller,
ES 16" Truss Tube Dobsonian and Orion XT8 with Nexus II DSC via Sky Safari Pro,
Celestron Luminous 31mm, Meade MWA 21mm, 15mm, 10mm, and 5mm EPs
Celestron Skymaster 15x70
and 15x25 binoculars
20/20 or better vision in both eyes due to recent cataract surgery!!!
"The LORD by wisdom founded the earth, By understanding He established the heavens" - Proverbs 3:19


 

Thank you, Darryl  -  glad it was helpful!  

On Sun, Aug 23, 2020, at 02:11, Darryl Ellis via groups.io wrote:
Outstanding document Robert.  I only meant to scan it while here at work, lol, but found myself going through it in a lot more detail than I had planned. 

Thank you for explaining the heavy east and camera heavy balancing.  For some reason I have had trouble getting my head wrapped around that concept.  However, your explanation made it apparent.

You may recall that at one point I posted that I was getting five minute subs with my Exos 2 using an RC6.  Balance and proper guide scope were the key.  Well I have returned to a modified version of that, but have not yet repeated those results.  This made me start thinking about how I can better balance things and improve the performance of my setup.

Your guide provides the information I need to deep dive into making the necessary improvements.

I really appreciate your work and sharing it with us.  Thank you.

Darryl
--

DHEllis59, Dover, DE

Astro Tech RC 6 w Pegasus Focus Cube and QHY10 OSC Camera
Orion ST 80 Guidescope and QHY 5 III 290c Guide Camera 
Explorer Scientific EXOS GT 2 With PMC Eight Controller,
ES 16" Truss Tube Dobsonian and Orion XT8 with Nexus II DSC via Sky Safari Pro,
Celestron Luminous 31mm, Meade MWA 21mm, 15mm, 10mm, and 5mm EPs
Celestron Skymaster 15x70
and 15x25 binoculars
20/20 or better vision in both eyes due to recent cataract surgery!!!
"The LORD by wisdom founded the earth, By understanding He established the heavens" - Proverbs 3:19



--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Tim Huseby
 

Robert,

     I keep getting bounced back to the main front page when clicking the link for your tuning note. I would love to read this and see what I can do with my exos2.

Tim
--
Tim
Las Vegas
Just starting in this Hobby, I have been doing wildlife and landscape photography. 
Mounts
Exos2-gt  PMC-8, Celestron Alt/Azimuth 

Scopes/Lenses:
Celestron SLT 130, Olympus 7-14,12-40,40-150 Pro and a Canon FD 500L

Cameras: 
Olymous om-d E-M1 Mkii,


 
Edited

Tim,
 
Hope you find it useful!  :-)
Did you subscribe to the Mounts forum?   Add that and it should work.
Look at Main / subgroups menu on the left of your browser.
 
- Bob
 

On Mon, Aug 24, 2020, at 12:42, Tim Huseby wrote:
Robert,
 
     I keep getting bounced back to the main front page when clicking the link for your tuning note. I would love to read this and see what I can do with my exos2.
 
Tim
--
Tim
Las Vegas
Just starting in this Hobby, I have been doing wildlife and landscape photography. 
Mounts
Exos2-gt  PMC-8, Celestron Alt/Azimuth 
 
Scopes/Lenses:
Celestron SLT 130, Olympus 7-14,12-40,40-150 Pro and a Canon FD 500L
 
Cameras: 
Olymous om-d E-M1 Mkii,
 

--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Tim Huseby
 

Robert 

    got in now thank you!
Tim
--
Tim
Las Vegas
Just starting in this Hobby, I have been doing wildlife and landscape photography. 
Mounts
Exos2-gt  PMC-8, Celestron Alt/Azimuth 

Scopes/Lenses:
Celestron SLT 130, William Optics Star 71 app, Olympus 7-14,12-40,40-150 Pro 

Cameras: 
Olymous om-d E-M5 Mkii, SBOG STF8300M


Tony
 

Robert, Thanks for writing up this document.   

I recently consulted it quite a bit while tracking down the cause of my RA sawtooth error.   Ultimately I found the bearing preload on the RA worm shaft was far too much.  The shaft felt gritty and notchy and hard to turn by hand.  Unfortunately the bearing retainer was so tight that it couldn't be removed even with a piece of plate steel, notched and held in a vice.  It simply sheared off the soft aluminum, leaving me no choice but to use a pair of pliers and sacrifice the threads.  I can no longer replace the lock nut, but luckily the fit is so tight, no lock nut seems necessary.  Anyway, reducing the preload allowed the worm shaft to spin smoothly, and has removed the vast majority of the RA error I was seeing.  From my understanding, the retainer should have been at or just over finger tight.  I would estimate mine to have been somewhere around 30 to 40 ft lbs from the factory.

My mount also had a high degree of friction on the RA axis with the clutch loose.  The fit between the worm drum and the RA shaft was tight.  I did wind up polishing the drum and RA shaft as mentioned by the myriad CG5 and LXD75 hypertuning threads online.  There was also a bit of deformation in the aluminum on the end face of the worm ring side of the drum, possibly cause by the worm screw itself (Shipping bumps and bruises?).  I took care to sand and polish down the material that stood proud.  I can't remember if this side interfaced with a bushing or not.  I suspect that side is supported by the RA bearings but I could be mistaken.  Anyway, the RA still does not move as freely as the DEC axis does with the clutches loosened, but it is much, much closer now.   I'ts considerably easier to get an accurate balance.  Previously, I had to move the OTA and judge by which direction slowed quicker.

Anyway, I mention these issues just in case you find them useful to caution others about in future revisions.

 

 


 

You're most welcome!

When I assembled the doc, I had to decide how far down in the weeds to go.  I know that there are others who have had a  sticky RA.  But as to how many, I had no clue, and the only way to fix that problem is to do a full teardown.  We're well out of 'adjustments' territory and so many folks are leery of cracking the covers in the first place - I certainly was.  So I sawed off short of full teardown and tried to stick to what most would need.

I think the worm bearing retensioning idea may have come from Kent via Jim McKee, back in the day - it's quite remarkable  how much difference it makes and if...err...you have a spanner... , how easy it is to make a real improvement.  The mount has good bones, but it can benefit from a little help in places.  :-)

I'm actually on my second mount head.  ES was quite good about replacing my first over a sticky RA, but the replacement had the same problem!   So that settled it, and I did the teardown and repair.  Here's a picture of me polishing trial-fit scuff marks out of the ring's ID.   

- Bob

On Mon, Aug 24, 2020, at 13:33, guitsboy@... wrote:


Robert, Thanks for writing up this document.   

I recently consulted it quite a bit while tracking down the cause of my RA sawtooth error.   Ultimately I found the bearing preload on the RA worm shaft was far too much.  The shaft felt gritty and notchy and hard to turn by hand.  Unfortunately the bearing retainer was so tight that it couldn't be removed even with a piece of plate steel, notched and held in a vice.  It simply sheared off the soft aluminum, leaving me no choice but to use a pair of pliers and sacrifice the threads.  I can no longer replace the lock nut, but luckily the fit is so tight, no lock nut seems necessary.  Anyway, reducing the preload allowed the worm shaft to spin smoothly, and has removed the vast majority of the RA error I was seeing.  From my understanding, the retainer should have been at or just over finger tight.  I would estimate mine to have been somewhere around 30 to 40 ft lbs from the factory.

My mount also had a high degree of friction on the RA axis with the clutch loose.  The fit between the worm drum and the RA shaft was tight.  I did wind up polishing the drum and RA shaft as mentioned by the myriad CG5 and LXD75 hypertuning threads online.  There was also a bit of deformation in the aluminum on the end face of the worm ring side of the drum, possibly cause by the worm screw itself (Shipping bumps and bruises?).  I took care to sand and polish down the material that stood proud.  I can't remember if this side interfaced with a bushing or not.  I suspect that side is supported by the RA bearings but I could be mistaken.  Anyway, the RA still does not move as freely as the DEC axis does with the clutches loosened, but it is much, much closer now.   I'ts considerably easier to get an accurate balance.  Previously, I had to move the OTA and judge by which direction slowed quicker.

Anyway, I mention these issues just in case you find them useful to caution others about in future revisions.


 

 



--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64