#iEXOS-100 Guiding Problems #iEXOS-100


Nathan P
 

Not sure if I'm supposed to start a new topic on this or post in one of the older ones.  I got the IExos 100 for Christmas and its been a rough journey so far.  It took a little bit but after a month or so managed to get some good pics of Orion Nebula using Explore Stars at 15 second exposures. Using any number of tools, including Explore Stars,  I have never been able to get exposures over 20 seconds.  So I decide to get a guide scope and camera.  Now, I'm having problems with PHd2 and guiding.  No matter what I do guiding jumps all over the place.  After physically inspecting the mount, I noticed a slight amount of backlash on both axis.  I followed the video for adjusting the backlash and adjusted them  appropriately.  When checking the backlash on the RA gear I am not able to adjust the screw for the worm gear, It looks like its been glued with locktite or something. I didnt have any play in that direction anyway so I moved on.  When manually rotating the gear and checking to make sure it isnt binding, I could feel something grinding.  I thought it might be the belt like others have suggested so I took the belt off and it still feel it after rotating the motor about 1/3 of a turn. Wasnt sure what was going on there so I got the worm gear and everything aligned properly and put it back together.  There is no more backlash as far as I can tell, everything rotates smoothly with no binding.  I make sure everything is balanced properly and I go back to PHd2 and do the calibration.  I get messages about  Questionable RA and Dec rates,  I also occasionally see pop up errors about guide pulse failed.  So I use the guiding assistant.  After its done measuring backlash it tells me that I have DEC backlash greater that 19000.  I have done this using both pulse guiding and ST-4 with basically the same results. I have rough polar alignment (I can see polaris in the polar finder).  I really dont know what else to do.  Should I post my ASCOM and PHd2 logs, am I missing something, or what am I doing wrong?

My equipment
Apertura Refractor 72mm 
Canon DSLR
Svbony guide scope 50mm
Svbony guide camera sv305 pro

newest version of ASCOM and ASCOM driver.
Using Ascom Device Hub
Connected through serial/usb to the mount
total equipment weight is about 8 pounds.


 

Nathan,
 
Starting a new topic about your specific problem is the right thing to do.  Astrophotography is a tough hobby.  Lots to figure out...hardware, software, technique, environmental conditions, suitability of targets to your setup, etc.  Don't get discouraged if it takes a while and takes some troubleshooting. 
 
I don't have an iExos-100, so I'm going to leave comments on specific mount adjustments to folks that actually have one, but I can leave you with some things to investigate:
 
1. Your "pulse guiding failed" error.  My google-fu tells me that this is basically a timeount.  PHD2 commands a move, and the mount is taking longer than expected to complete it.  Threads over on CloudyNights and Stargazers lounge point variously to incorrect PHD2 backlash settings, underpowered batteries, cable issues, etc.  Multiple possibilities, but that appears to be what its' complaint is about. 
 
2. Differential flexure.  I can't say whether this is involved in your problems or not, but it could produce something like the behaviors you describe, and it's a box you should be sure is checked.  This happens when the optical path to your imaging camera's chip and the optical path to your guide camera's chip, are able move with respect to each other.  This is bad...  You'd basically be looking for a scope that can move slightly in its shoe or rings, or a focuser rotator that's not locked down, or a camera that can shift a bit in its focuser - that sort of thing.  Those two paths need to be rigid with respect to each other.  I had that for a while when I was first getting set up, and even a tiny bit of play can create a problem.
 
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


Nathan P
 

Thanks for the response Bob.  The time out while guiding error I don't think is critical,  it just occasionally pops up.  I've spent many years doing tech support and its sometimes the 'little' or 'inconsequential' things that can be the key in solving an issue so I thought Id throw that in there.  I assumed power issues at first too.  Not thinking about the lower voltage, I was using rechargeable batteries at first.  That very quickly got changed to a 12 volt battery pack, and then recently I went so far as to run an extension cord and a/c power plug to rule out that possibility.  As far as flexure goes, The focuser tube, rotator and and everything are solid,  no movement.  The guide scope is tight in its mounting rings.  I even went so far is to run cable management so there's no pull on the cables at all when the telescope is slewing. My google-fu is strong as well and it's only after countless nights researching and trying everything I could find that I decided to post here, BUT just to make sure I didn't miss anything I double checked all your suggestions and I THINK I'm good as far as that goes.  

I honestly thinks its a backlash problem, or at least part of it is.  What I don't know is what is considered an 'acceptable' amount of backlash for this mount or even in general?  I'm under weight capacity but I cant help but to wonder if I'm just pushing the limits of this mounts capabilities and maybe I should start looking into upgrading.  

Nathan P


 

Nathan,
 
I doubt you're pushing the limits.  While ES initially aimed the mount at the light and simple end of things, owners have had a good time pushing the limits as an astrophotography mount, which begat the AZ adjuster, the tripod upgrades, etc...  With the right upgrades, these little guys can get well inside the range of my larger EXOS2.  So no, as far as the type goes, you do not look like you're stretching it at all.  Have a look at the astrophotography work being posted here.  Something else is going on.
 
Some backlash just comes with the territory.  I have a ring and worm gear, you have a wheel and worm gear, but in both cases the the spacing between the gears is fixed.  And the two gears are not, and cannot be, perfectly round.  So you adjust to enable minimum clearance, just short of binding.  Which means that in-between the points where you *almost* bind, you will have a larger gap, which gives you backlash.  It is what it is, but for what it's worth, that wheel gear of yours is likely a better arrangement than my ring gear.  
 
The way you minimize the effects of backlash is with weight bias.  In general, you want your RA to be East-heavy (ie: always lifting weight), and your DEC to be camera-heavy.  There's also a school of thought on minimizing DEC guiding (one direction only, no guiding at all, etc.).  For now, at least, I'm going with less-is-more and have PHD2 fairly insensitive in DEC, but still guiding. 
 
I re-read your original post, and did wonder if there was a bearing issue.  Again, I do not have an iExos-100 and all I have to go on is Alex's adjustment video for the physical arrangement, so don't go by me, but one problem that does come up from time to time on the EXOS2's is a problem with the worm block bearings.  
 
On my the EXOS2, this comes in three flavors:
- Bearing not sufficiently tensioned, permitting lateral play on the worm shaft
- Bearing over-tensioned, and squeezing the bearing makes it stick and run rough.  Adjust the tension and it smooths out.
- Bearing defective and needs to be changed out.
 
Again, not a diagnosis, just something to investigate.
 
While I can't help with mechanical tuning specifics for your mount, my Tuning Notes doc for the EXOS2 is over in the Files/User Contrib section and you're welcome to any conceptual help you can glean from it.  
 
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