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Belt tracking issue after adjusting EXOS2 RA drive train.


John
 

I just adjusted my EXOS2 RA drive train for the first time using Bob Hoskin’s EXOS2 tuning guide.  I am having an issue where the belt tracks to the far left past the edge of the large gear/pulley.  I have moved the large gear as far left as I can without it hitting the end of the worm gear housing.  But the belt stills runs beyond the left edge of the gear.  Since I took the picture, the belt has drifted even farther to the left and is now rubbing on a screw head on the right side of the worm gear housing.

The belt is tight and is centered on the smaller pulley/gear.  See the attached image.

With the belt rubbing the screw head, the mount is currently unusable.  How do I get the belt to track properly on both gears?

John

--
John Koors
Wind Point, WI
Mounts
: ES EXOS2-GT PMC-Eight 
Scope: Meade AR-5 Refractor
Cameras:  Polemaster, ZWO ASI224MC, Nikon Z6, QHY163M, QHY163C, QHY filter wheel
Software: APT, TheSkyX Serious Astronomer Edition, PHD2, PlateSolve2, ExploreStars, SHP


 

John,
 
I would guess that something's tipped.  If the two shafts are not parallel, then one side of the belt would have more tension on it than the other, and it would drift like that.
 
It's pretty easy for the worm block to get tipped - ie: not perpendicular to the the ring gear.  That's part of the point of the shimming step in the doc.  Better gear mesh, and as a byproduct of that, the worm block is more likely to be square with the motor, as well.  
 
So... the simplest thing would be to revisit section 7.4 and take another run at squaring the worm block.  
 
Also, in Section 7.3... is the middle adjustment screw on your worm block a setscrew, or a capscrew?  
 
- 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


Wes Mcdonald
 

John

That last point of Bob’s is important.  That screw head can interfere with your motor when you go to position it.  The motor ends up rocking on the head of the screw and that prevents you from getting things parallel.   Replace it with a set screw to get rid of the head.  There is apparently just enough variability in the belt lengths or other mechanical tolerance that the screw is either just barely out of the way or just barely too high. I had one axis the interfered and one that didn’t.

Wes 


--
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


John
 

Gentlemen,
Thanks for the quick response.  I did replace the capscrew with a setscrew, so there is plenty of clearance between the end of the setscrew and the motor housing.  I did use shims to square the motor housing to the worm gear.  After tightening and adjusting all 5 bolts, I measured the gap between each side of the worm block housing and the RA housing with a micrometer.  They are within .1 mm .  
When tightening the single bolt to attach the motor assembly to the RA frame, I tried twisting it to each side to see if it affected the belt tracking.  The amount of side to side movement is very limited and it made no difference.  So, my next recourse is to tweak the two outer screws of the mesh gear block to adjust its angle to the ring gear axle in order to get the two gear axles parallel.

Can I assume that the current tracking of the belt indicates the axles are diverging from each other and that I need to bring the tips closed together?

Thanks for your help.

John
--
John Koors
Wind Point, WI
Mounts
: ES EXOS2-GT PMC-Eight 
Scope: Meade AR-5 Refractor
Cameras:  Polemaster, ZWO ASI224MC, Nikon Z6, QHY163M, QHY163C, QHY filter wheel
Software: APT, TheSkyX Serious Astronomer Edition, PHD2, PlateSolve2, ExploreStars, SHP


 

On Thu, Sep 17, 2020 at 10:54 AM, John wrote:
Can I assume that the current tracking of the belt indicates the axles are diverging from each other and that I need to bring the tips closed together?
John,
 
That's pretty much what I worked through on on mine, although in my case it was the small pulley's keeper that it persisted in going towards.   
 
One thing to add, though, is that there appears to be more than one type of belt movement, one significant, and one not.  Mentioning this because you didn't say how the pulley was being driven when you ended up where you are.
 
Case #1: Persistent misalignment, where the belt moves against (in my case, the keeper) quickly and consistently, just with hand turning, and it rubs where it stops.   This produced a very prominent 133s wave on an unguided PHD2 log, and sometimes even a prominent 13s wave (from individual pulley teeth).  These short-period waves did affect my guiding (ie: more error to compensate for), and quieting them down made quite a difference for me.
 
Case #2: Behavior #1 is not present, BUT... If the axis is driven under power in one direction, the belt drifts slowly to one side, and if driven in the other direction under power, it drifts back.  I have no explanation as to why this happens during a directional change, but the lateral drift of the belt does not appear to be forceful, and it doesn't affect my guiding.  I harbor a suspicion that the belt movement might make a difference until it settles, but whatever effect that is, is tiny.
 
Hope this helps...
 
- 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