DEC axis not moving in certain position. Belt slipping. #EXOS2


Peter Danek
 

Update to: https://espmc-eight.groups.io/g/MAIN/topic/exos2_working_few_seconds/80714857?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,80714857

Thank you ES Germany for solving my RMA claim. I have received a new PMC 8 unit and it is working as expected. But, I never had such bad luck as I have now.

Because I can now control the mount I found a big problem with the DEC. When slewing and the worm/motor is near the locking clutch, the DEC stops to move and the belt is slipping. I noticed that when the worm/motor is near the clutch, and I lock/unlock DEC, the big wheel of the worm is moving. It is also impossible to move the wheel of the worm near the locking clutch when DEC is locked. However, I can move it if it is the opposite of the locking clutch.

It seems like when I lock the DEC the inside parts move. 

I can make a video of the problem if it is not clear to understand.

Is it something I can adjust or I'm looking at another RMA process? :(
--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


Peter Danek
 

Here is a video of what I mean, the worm moves when I lock DEC.

Video in the attachment.
--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


 

Peter,
 
Sorry, but I don't understand your problem statement.  Are you saying that the DEC axis is binding in a certain position?  Clutches should always be on, if the mount is under power.  
 
If that's all it is, and your scope is reasonably balanced, then all you likely need is a bit of an adjustment.  There are not a lot of moving parts in these mounts, and it is not unusual for some owner adjustments to be needed from time to time. 
 
If the motor is running, the set screws on the two pulleys are snug, and the belt is reasonably tensioned, then the worm gear will be driven by the large pulley.  If the worm is not moving, then the most likely thing holding it back is a too-tight mesh (binding) between the worm gear and the ring gear that surrounds your axis.  This can happen, because the clearance between the two gears is fixed, but the two gears are not (and cannot be) perfectly round.  So the goal of adjustment is to achieve the smallest amount of clearance that still avoids binding on high points between them. 

I don't know what an ES pre-delivery test of the mount would entail, but if bind points occur, they will be at particular locations and there's no predicting whether a short test would actually traverse a given bind point and reveal such a problem.  In any case, if all that's needed is a gear mesh adjustment, that's pretty straightforward.
 
If I've understood your problem correctly, then the doc in the link below may help you, with this and perhaps other things as well.

https://espmc-eight.groups.io/g/MAIN/files/User%20Contributions/EXOS2PMC8_TuningNotes_v2.pdf

Hope this helps...

- Bob

--
Mounts: ES PMC-8 EXOS2, Serial
Scopes: SW 130P-DS, SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM 6.3, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Peter Danek
 

Hi Bob,

have you seen my video? I will try to do another one to explain it more. I have seen your document before I posted this and I exactly know where the problem is. The mesh is too tight and the worm is not moving when it is near the clutch. If the worm is in the opposite position down from the clutch it is loose. When I lock the clutch the cylinder with the mesh inside moves up pushing on the worm(see the video).

It doesn't seem right to me. There should be no pressure after locking the clutch. 
--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


Peter Danek
 

1. picture: the mesh is too-tight, belt slipping, the worm is not moving


2. picture: the mesh is too loose, a huge backlash

--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


 

Peter,
 
Yes, I saw the video before I responded.  Really couldn't figure out what you were trying to illustrate.  There's a small amount of shifting back and forth by the large pulley, but that could just be the worm pushing on an obstruction and then easing back from it as you release the clutch. Note that the belt is moving along with the large pulley.  
 
Unless badly under-tensioned, the belt cannot slip. It is toothed, as are the pulleys, and it does not stretch.  Now, we have seen the odd pulley with loose setscrews, but in those cases, it is a pulley slipping on a shaft (not the belt) and the behavior would be different than what you show in your video.   
 
When you engage the clutch, a small 'brake shoe' presses on the side of the ring gear, and that friction engages the outer shell of a given axis and transmits movement from the ring.  With the clutch disengaged, the outer shell is free to rotate, independent of the ring gear (which still remains engaged with the worm).  So a scenario where the motor drives the worm into an obstruction, and then you see a bit of bounce-back when you release the clutch, wouldn't surprise me.  

- Bob
 
--
Mounts: ES PMC-8 EXOS2, Serial
Scopes: SW 130P-DS, SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM 6.3, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Wes Mcdonald
 

Peter:

When the motor stalls, the belt does not slip as Bob mentioned.  Instead the motor simply does not move but it makes a huge racket, like a coffee grinder.  I haven't seen the movie.  How does it sound?  

If you are binding, then you just have to loosen the mesh.  And live with the consequences.  Use Bob's paper to set it up as well as it can be.  Dec backlash is just a fact of life with these mounts.
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


Peter Danek
 

Thank you, guys. I understand what you are saying but there was no conventional way of adjusting and fixing my issue. After tinkering with it all day I finally found a fix and now it's working with no issues. 

--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


Sebastian
 

Nice, I found out the factory used  inch and metric Allen screws for the dec motorbox 😕


 

Peter,
 
That's a surprise!  Are you showing that the worm block was not sitting flush despite being fastened down, or something else?  Here's a candid shot of mine, from a bit different angle - no room for shims.
 
- Bob



--
Mounts: ES PMC-8 EXOS2, Serial
Scopes: SW 130P-DS, SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM 6.3, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Peter Danek
 

Bob,

as I said, the ring gear moves after locking the axis for some reason. This causes the mesh between the worm and ring gear to be too tight on one side and too loose 180 degrees on the opposite side.

So I had to push the worm block slightly lower by the shims to get even mesh tightness around the ring. Strange, but it's working now as it should be.
--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


Wes Mcdonald
 

Peter

If this proves to be universally true you just may be the next steely eyed rocket man. Really this problem has always been ascribed to eccentricity.  But if in fact it is addressed by better alignment of the worm and wheel center lines...this is huge.

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


Peter Danek
 

Wes,

thank you but am I understand it right? You are saying, that the issue I was describing and fixing is simply a feature of the DEC ring gear and a worm? That the mesh tightness is not even 360 degrees around the ring by default?

Because that was my problem, the misalignment of the worm to a ring gear. Pushing the worm box slightly lower causes better alignment of the worm. It is still, not 100% perfect and you can play with it more but I'm happy now as it is.
--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290


Wes Mcdonald
 

The deal is with this mount at this price point the mechanics are not perfect.  So you will find that the mesh tightness is not uniform around all 360 degrees.  This means that when u set the tension you need to rotate the thing manually all the way around.   

But great catch. I am sure this is something that needs adjustment (your new shims) or at least looked at for people who want to tune things up.

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


Peter Danek
 

Well, I hope that this fix is not my isolated case only. Someone should try it to confirm if it helps to get uniform mesh tightness 360 degrees around. My "shims" are just folded sticky note :D Different shim thickness will have different results.
--
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras:  Canon T3i, Canon XS, SV305 Pro - IMX290