#EXOS2 My RA on my mount is wiggling, Causing Star Trailing!!! #EXOS2


nickerson.joseph@...
 
Edited

HELP!!! I have been using the EXOS2-GT w/PMC8 for about 6 months and have been mostly happy with the purchase. Most my frustrations stemming from just being new to the hobby. I use my mount for astrophotography only and noticed over the last month I was losing more and more subs to the same issue of  very slight star trail. My last few sessions though I am now losing over 50% of my subs regardless of exposure time. My polar alignment is spot on using shape cap, my guiding stays under .20 on RA and DEC. Today as I was making sure all my equipment was secure when I noticed that there is "play" on the mounts RA, no matter how much a crank the clutch, I still get movement, with or without power on the mount, Parked or Un-parked. My DEC is solid as a rock. I can only assume this is my issue. I have been calling Explore Scientific all day today but no one is answering. I am not sure where to go from here...Any assistance would be greatly appreciated. I have attached a sub of the star trail and a video of the play. Sincerely.....


NewAP
 

I have similar issue with IEXOS-100, there might be several reasons I suspect:
First is the periodic error due to the imperfection of the gears, it causes the rocking along RA.
secondly seems the tracking rate is slightly off but I guess it will take some effort to change it, but you can try tweak it a bit by setting the custom sidereal rate, +-2 to start with.

Best,
Yi 
--
Canon 6D, Sigma 150-600mm, IEXOS-100


nickerson.joseph@...
 

Are you saying it's suppose to wiggle like that? 


 

Joseph,

This hobby is an endless source of problem-solving opportunities  :-)

Just tossing some things out as grist for your mill...

If you tell me that your mount axes wiggle, well, you may need some mechanical adjustment (see link below).  
BUT... some play in the ring/worm gear connection is entirely normal, so while it's good to keep a mount well-adjusted, there are limits to the mechanical perfection we can achieve. 

Having said that... if you tell me that your guiding looks good, but your stars trail anyway, then I'd wonder about the dreaded "differential flexure". 
Basically, guiding well requires that the two optical trains (guiding and imaging) be absolutely rigid relative to each other. 
Relative movement of scopes in rings, focuser rotators, cameras in focusers, etc... all bad.   
I would guess that if guiding looks good, there may be motion in your imaging train.  On my scope, it was a focuser rotator.  Very convenient for visual use, but its inherent play was a bad idea for my imaging.  I locked its little grub screws down with extreme prejudice and saved the day!  

FWIW...

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

--
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


Walter Vinci
 

Hi Joseph,

I am totally new to the hobby too (hi everyone :)! ), actually just a couple of nights out with autoguiding, but my ES PMC-8 EXOS2 has a similar (even wider I would say) play on RA and I have no such problem (doing about 2” RMS but with round stars). 

On Jan 7, 2021, at 2:56 PM, Robert Hoskin <devonshire@...> wrote:

Joseph,

This hobby is an endless source of problem-solving opportunities  :-)

Just tossing some things out as grist for your mill...

If you tell me that your mount axes wiggle, well, you may need some mechanical adjustment (see link below).  
BUT... some play in the ring/worm gear connection is entirely normal, so while it's good to keep a mount well-adjusted, there are limits to the mechanical perfection we can achieve. 

Having said that... if you tell me that your guiding looks good, but your stars trail anyway, then I'd wonder about the dreaded "differential flexure". 
Basically, guiding well requires that the two optical trains (guiding and imaging) be absolutely rigid relative to each other. 
Relative movement of scopes in rings, focuser rotators, cameras in focusers, etc... all bad.   
I would guess that if guiding looks good, there may be motion in your imaging train.  On my scope, it was a focuser rotator.  Very convenient for visual use, but its inherent play was a bad idea for my imaging.  I locked its little grub screws down with extreme prejudice and saved the day!  

FWIW...

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

--
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


nickerson.joseph@...
 
Edited

The same issue was accuring with my guide scope mounted on center line, see attached picture. I am having a hard time rapping my head around any play in the mount with clutches locked down being normal.


 

Joseph,

Play (backlash...) in the gears?  Some is indeed normal.

Gears, shafts, bearings...all have tolerances.
And the spacing between the ring and worm?  It's fixed.  No play in that. 
So the best you can do is adjust the two gears to be as close as possible without actually binding. 
And where the spacing opens up...you get play/backlash.  You counteract that by managing balance.

I'm looking at your setup picture, and I see a very long focuser tube with a (heavy) filter wheel and camera at the end of it.  Is there unwanted motion there, at the sensor end?  No idea, but given your problem description, I'd be taking a close look.  Remember, you're looking for microns...

Again, FWIW.  Hope this helps...



On Thu, Jan 7, 2021, at 17:09, nickerson.joseph@... wrote:

[Edited Message Follows]

The same issue was accuring with my guide scope mounted on center line, see attached picture. I am having a hard time rapping my head around any play in the mount with clutches locked down being normal.

Attachments:
  • 20210101_112422.jpg


--
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


nickerson.joseph@...
 

Robert I appreciate your help. I understand the concept of backlash. In the aircraft maintenance world we always called it play. Tomato, Tomato. I have been up and down my image train a half dozen times looking for unwanted motion and could find none. And it seems the issue is worsening over time and I can say with 90% assurance that backlash wasn't always there. I opened up the side panel for the RA to inspect the gears and saw nothing askew and when I wiggled the scope again on the RA, the gears did not move. Wouldn't the gears move if the play was indeed backlash. My gut/maintenance intuition is telling me that there is something wrong with the Clutch allowing the play which turns into a slight vibration that effect the image during a hard motor push, which is why not all my subs are bad, but enough to warrant mega frustration. I don't seem to have any issues with star trails along the DEC and that sucker is solid with zero wiggle/jiggle/backlash/play. In aircraft maintenance that is called check the other side to see if it's doing it, if its not then that is most likely the issue.  Also, does anyone know why Explore Scientific isn't answering their phone.... 


 

Joseph,
 
Re: The Clutch...
If you scroll down the stardeck observatory link, you'll see some rather decent exploded photos of an LXD75, our EXOS2's progenitor.  Our mounts have bearings on all axes and the bushings/spacers are a bit different, but the general arrangement of things is much the same. 
If you scroll to the RA assembly diagram, to the right is a dotted circle that encloses the "axis rotation lock assembly" (aka clutch, brake, etc.).  A lever, a screw, and a little dot of something, which is effectively a small brake shoe.  I've attached a photo of mine, taken when I had my mount apart.  Turn the lever and the brake shoe presses on the ring/drum gear's side.  This mechanically links the ring gear to the outer shell of a given axis, so the motor can rotate it for tracking and slewing.  Disengage the clutch and the axis is free to rotate for balancing.



There's not much to go wrong with it, or to adjust.  I believe that the screw in the lever can give you a bit of control over tension, but that's about it.  

Re: wiggling...
The ring gear is driven by a worm gear.  Worms drive, they aren't driven, so you won't see your motor pulley wiggle.  If the axis is moving, the usual cause is just normal backlash that you just have to manage around.  But there is one other possibility, and this might cause trailing. Take a look at Section 7.3 in the tuning doc I linked.  That deals with adjusting the tension on the worm gear shaft.  They are sometimes mis-tensioned, either too tight or too loose.  If too loose, the worm could shift along its length as rotational force on/from the axis varied.  While the worm will refuse to be driven, I suppose it's possible that it might shift.  Easy enough to check, but you'll need to pop the covers to do that.  
 
Hope this helps!
--
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


Tyler Bowman - Explore Scientific Customer Service <Tbowman@...>
 

Hey if you could send me a email at tyler@... we can figure out whats going on.


nickerson.joseph@...
 

Email is sent, when I clicked your link it posted as tyler@explorescien, I assumed it was tyler@... and sent it.


jdavis1278@...
 

There are a couple of videos on Youtube about adjusting the RA wiggle that happens sometimes with the IExos100 and Exos2... I know the adjustment for the iexos100 requires you to take the cover off and do some simple adjusting to the screws holding the gears on. 

Iexos100 vid: https://youtu.be/mLXE_BMKVAw
I'm not sure if that's helpful or if they're too dis-similar for that to help


Jennifer Shelly
 

Joseph:

I used to own an Exos-2 PMC-8 and have been through the tuning exercise multiple times.  It appears your image of the star trail is exposing nice round stars for the majority of your exposure time then something happens and the stars appear to be shifting to the left for a small amount of the exposure time.  Does that sound correct?  The reason I say this is because it appears you have a bright star and a faint star right next to it like a ghost or like the mount is skipping.

A few things come to mind.  Is it possible a cable is getting snagged? Is your counterweight fully secured and not able to slide down the counterweight bar? Are you absolutely sure you are balanced in both the RA and DEC axis? My old Exos-2 had stiction in the RA axis and when I thought I balanced I really was not. Have you manually rotated the RA axis by hand to check for any tight spots on the worm ring gear? Try rotating by hand 180° and see if your wiggle is better or worse.  In the video you demonstrate wiggle by grabbing your guide scope and moving it side-to-side.  What does the wiggle look like when you do the same to the counterweight bar? If the wiggle is less then you will need to figure out what is causing the wiggle in your imaging train.  You mentioned that you have tightened the RA clutch as far as it will go.  Since the worm wheel gear is made out of aluminum it is possible create an indent in the worm wheel gear from over tightening which would be exaggerate the natural high and low spots on the worm ring gear.

Sorry if this is too much, I just wanted to list everything that came to mind. I hope this helps.
--
Sincerely,

Jennifer Shelly
AstroPorch, VA

Mounts
: ES PMC-8 G-11, ES PMC-8 iEXOS-100
Scopes: ES ED127 FCD-100, Askar FRA 400, ES Levy Comet Hunter, ES N208CF, QHY Mini Guide Scope, Solomark F60 Guide Scope
Cameras: QHY600M, QHY128C, QHY168C
Misc: MoonLite CFL 2.5 / High Res Stepper / V2 Mini Controller, Baader SteelTrack NT / SteelDrive II, Baader UFC, Optolong 2" L-Pro / L-eNhance, QHY CFW3-L, Baader 2” LRGBSHO CCD
Imaging Software:  NINA, APT, SharpCap Pro
Processing Software: PixInsight, Lightroom, Premiere Elements


nickerson.joseph@...
 

After watching the video provided by jdavis I am pretty convinced that is my issue. I have check and rechecked everything you have mentioned. I am hoping to get in touch with Explorer Scientifics customer service before I open it up given that the mount is only 6 months and still under warranty. Thanks for your suggestions.