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Tuning backlash on iExos 100


Vijay <vijaysam@...>
 
Edited

How do you tune backlash on iExos 100?

I tried to do a rock test on both RA and DEC. DEC seems to be proper without any shifting. But RA is shifting a bit when I move it. I opened to see the gears and I can see that it is shifting for sure.

How do you fine tune the backlash on iExos 100. I was referring to the video https://www.youtube.com/watch?v=x79akiJO3pU for HEQ5 mount though to get an idea of backlash. Around 8:04 it talks about the rock test which is what I did to find if there was backlash.

Any  pointers, experiences would be helpful.


Jeff Weiss <jeffweiss2131@...>
 

Thanks for asking great questions Vijay. I am following every response. These guys are very helpful.

Thanks guys!

On Wed, Sep 9, 2020, 1:46 PM Vijay <vijaysam@...> wrote:
How do you tune backlash on iExos 100?

I tried to do a rock test on both RA and DEC. DEC seems to be proper without any shifting. But RA is shifting at bit when I move it. I opened to see the gears and I can see that it is shifting for sure.

How do you fine tune the backlash on iExos 100. I was referring to the video https://www.youtube.com/watch?v=x79akiJO3pU for HEQ5 mount though to get an idea of backlash. Around 8:04 it talks about the rock test which is what I did to find if there was backlash.

Any  pointers, experiences would be helpful.


Vijay <vijaysam@...>
 

I think I figured out where to tune for RA.
At the end of the worm gear, there is a large screw.Tightening/loosening seems to reduce the shift but not all of it though. There is some shift still, though it has reduced reasonably.

Need to try the mount out once the sky is clear and see how well it performs in PHD2.


Wes Mcdonald
 

Vijay

Backlash on the Exos2 (and 100) comes from two sources:  The preload on the worm bearings (which is what you adjusted) and the mesh between the worm and the wheel gear.  Once the preload is just enough to ensure the worm does not move left and right (along its axis) then it is set correctly.  Most have found that if you overtighten it, the worm picks up a cogging action from the ball bearings and while we have not quantified what effect this might have, most remove it by having just enough preload.

The second issue is how tightly the worm meshes into the wheel.  This is one of those things that is a compromise.  If you get it too tight, then the mount will bind and stall.  If it is too loose, then you have backlash.  You can find a paper by Bob Hoskins that explains how to set the backlash (and other good to know stuff) in the Files section of the MAIN group.  

The backlash in the RA axis is less critical, because the mount is always being driven in the same direction in RA.  Even when guiding, the drive never reverses, it is just slowed down a bit or sped up a bit.  Dec is another story as guiding will cause dec to reverse directions at which time the gears will disengage.  So you want to really work on the DEC mesh to get it just as tight as you can without causing a bind. 

The tricky part is that the wheels are not round and the shafts may not be exactly eccentric.  This means there will be areas of loose mesh and areas  of tight mesh.  You have to find that mesh adjustment that does not bind but minimizes the loose part -- and for that you have to check the mesh 360 degrees around the wheel.

Hope this helps
Wes.


On Wed, Sep 9, 2020 at 6:33 PM Vijay <vijaysam@...> wrote:
I think I figured out where to tune for RA.
At the end of the worm gear, there is a large screw.Tightening/loosening seems to reduce the shift but not all of it though. There is some shift still, though it has reduced reasonably.

Need to try the mount out once the sky is clear and see how well it performs in PHD2.


--
Wes, Southport NC
EXos2-GT PMC-8, iExos 100
ES ED 127, 10" LX200GPS+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired


Vijay <vijaysam@...>
 

Wes,

Thanks for responding.

DEC on my mount seems to be quite good. There seems to be no backlash.

Are you talking about  the document at /EXOS2PMC8_TuningNotes_v2.pdf ?
I am trying to find that file, seems its not available at https://espmc-eight.groups.io/g/MOUNTS/files.

Or is it a different document your talking about?

Thanks,
-vijay


Jeff Weiss <jeffweiss2131@...>
 

Robert moved that file to the main forum file area.


On Wed, Sep 9, 2020, 7:55 PM Vijay <vijaysam@...> wrote:

Wes,

Thanks for responding.

DEC on my mount seems to be quite good. There seems to be no backlash.

Are you talking about  the document at /EXOS2PMC8_TuningNotes_v2.pdf ?
I am trying to find that file, seems its not available at https://espmc-eight.groups.io/g/MOUNTS/files.

Or is it a different document your talking about?

Thanks,
-vijay


Vijay <vijaysam@...>
 

Can I have the link for the file?


Jeff Weiss <jeffweiss2131@...>
 

I could not find it either.

On Wed, Sep 9, 2020 at 8:07 PM Vijay <vijaysam@...> wrote:
Can I have the link for the file?


Vijay <vijaysam@...>
 

Thank you Jeff.


 

Go MAIN>Files>User Contributions

I'm starting to think I can't win on this...

https://espmc-eight.groups.io/g/MAIN/message/7962

--
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


James Ball
 

I have looked at the Tuning guide a few times but on the iEXOS-100 there are just two cap screws holding two separate blocks, one at each end of the worm gear, and no screw in the middle.  The worm is not mounted in a single piece block like on the EXOS-2 I believe.  I adjusted my RA mesh because it had quite a bit of wobble and had to loosen the two cap screws and carefully move them to reduce mesh but while keeping the gear square with the belt.  I think mine is a little too tight as it will bind if not perfectly balanced but I really don't want to have it apart again unless I have to.  Maybe I am not seeing it correctly, but that is what I had to do.
--
James Ball
Dawson Springs, Ky
Mounts: iEXOS-100
Scopes: Meade ETX90RA(deforked now) Sky Watcher 150MCT
Camera: ZWO ASI 120MC-S
Software: Explore Stars Android, ASCOM, Stellarium Scope, Stellarium, AS!3, SharpCap, RegiStax6.


Vijay <vijaysam@...>
 

I finally got the little backlash in RA fixed by seeing the video https://www.youtube.com/watch?v=mLXE_BMKVAw
Now things look good on RA where I don't have any wobble.


Doug Walker
 

Thank you for the link to this video! Backlash gone. (I had to do the third option that he mentions in one of the comments to loosen the whole plate)