Re: Possible defective unit #iEXOS-100 #TECHNICAL


First off, thank you for that detailed analysis Jerry, appreciated.
The old post was an interesting read, I appreciate the difficulty of making changes to the chip and it sounds like increasing the current to the motor might be an option.

The first video I attached was made with a Meade LX65 Cassegrain @ 1900mmFL x 127mm. I think I used a 25mm eyepiece and my trusty Celestron Neximage CCD at 720x480 @ 25 FPS. I may have used my 2x doubler but I don't recall for sure, sorry.
The iexos is on the latest firmware. Although I was managing the mount via the ASIAir, the camera was plugged directly into my laptop. I recall switching the ASIAir tracking mode between Sidereal and Lunar tracking to see if the issue would go away and it was present in both modes.

I can try and provide more information - just let me know what you need.

I agree with your comments; I don't notice the oscillation issue when imaging with my wider-field Orion 80x400mm refractor. The scope is over 30 years old and I'm still getting nice round stars and 2-3min guided exposures using the iExos. I could probably push it even longer and have similar success. To your point, I only notice the issue with the higher focal length LX65, narrower field of view with planetary/lunar viewing/video. 

The LX65 is about 6.2Lbs and I needed both counter-weights almost fully extended to balance the mount. I feel confident the balance was fairly good but find there's some friction with the mount when trying to balance so it's as good as I could get it. 
I also thought that the increased mass/inertia of the bigger scope and perhaps slight off-balance configuration might contribute to making a small issue have a bigger than normal impact visually.

My goal for that evening was to try and learn how to stack video to produce some nice pictures of the moon and perhaps Jupiter using this video-stacking technique when the oscillation became apparent.
We had already started this thread when I received the LX65 so I wasn't too worried if the issue should appear as others had indicated I could stack/process the issue away.

However, we were just viewing the Moon and Jupiter (and for that the long FL and magnification is required) and people were looking through the eyepiece and amazed at the clarity but then looked up and said, 'Why's it wobbling?'
I felt a little silly trying to explain it - lol.

It's like trying to explain why the radio doesn't work on your brand-new Ferrari - lol.
It still goes really fast but it's still annoying :)

I get this hobby is technical and has a learning curve and requires practice and tinkering - that's kinda why I like it. 
But I'm hoping we can get this sorted out.

@ Wes, i'm going to do some digging and see if I can determine what's driving the ASIAir (ASCOM or other) and what exactly happens between Sidereal and Lunar tracking - I don't see a 'Point'  mode for the ASIAir.
ZWO just released a new firmware version with a video mode so I'll see if this issue persists.  I'm aware we don't want to turn this into a third-party discussion but it seems others have noticed the issue with different non-ASI configurations.

Jerry, if there's a way to increase the current to the mount to minimize this, then I'm willing to try. Previous comments about power consumption when on battery noted.



On Sat, Oct 3, 2020 at 11:05 AM Jerry Hubbell - Explore Scientific VP Engineering <jrh@...> wrote:
On Fri, Oct 2, 2020 at 09:11 PM, Mario wrote:
Quick note, some others seem to be observing this same behaviour:
Appears here with lunar
This view of the iExos internals that seem to oscillate in time to what is being observed through the
Not sure if the second video is related bu seems to be....line the motor is pausing then 'catching up'
I would expect this motion to be smoothly tracking...not oscillating...
Hi Mario,

There is a documented 1.3 second oscillation in the motor driver chip which I have talked about previously ( ) as some of our customers identified on the G11. We identified this issue about 2 years ago but the magnitude of the problem is typically < 0.5 arc-second. In fact it has been demonstrated to be smaller than that as some users have reported an total RA guiding error ~ 0.5 arc-second including scintillation effects during long exposure imaging. This behavior does not affect long exposure imaging, nor lunar/planetary imaging at long focal lengths as the stacking software can manage the small amount of "jitter" caused by the motor driver. The only real observing that was impacted was visual observing at very high focal lengths typical when observing Mars, Jupiter, Saturn, etc.  Focal lengths of > 2500 mm when visually observing these planets were impacted.

At the time of discovery, after some investigation, we found that an increase in the motor current on the G11 helped to reduce this 1.3 second "jitter" significantly, although we also found that it depended on the equipment load and could be exacerbated by having weight at long moment arms which increased the inertial load. 

Based on your video, I made some measurements and assumed the following:

Video is a 1080p resolution image
The full width of the moon would effectively stretch the full width of the frame if centered
The width of the moon is 2160 km and 30 arc-minutes (1800 arc-second)
I measured the motion of the video using the crater Hell which is 33 km wide
I found that the oscillation (peak to peak) was about 1/2 the width of crater Hell, or about 15 km
The pixel scale for the image was about 2 km per pixel (2160/1080) or about 1.7 arc-seconds/pixel (1800/1080)
Based on this, the oscillation is equal to about (15 km / 2 km) * 1.7 arc-seconds which equals 12 arc-seconds peak to peak.

This is equal to about 2 arc-seconds RMS which is about 4 times what we would expect based on our previous experience.

It appears that there is something in your equipment configuration that could be aggravating the appearance of this tiny oscillation, perhaps the total load or how it is mounted.
If you could give me some details in that regard I would appreciate it. Also, it might be possible to increase the motor current setting to help mitigate this issue and reduce the 
magnitude of the oscillation.  

Again, it is important to realize that this motion is just one component of the motion you will see when observing the moon or planets at a large focal length either through the
eyepiece or via live video.  There is the natural drift in Declination, there is the local seeing conditions which can cause the motion to be at least the same magnitude or even more
than what you are seeing here.

Thanks for your report Mario.
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at
1010 S. 48th Street
Springdale, AR 72762

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home

Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!


Streetsville, Ontario

Mounts: iExos 100, Skyguider Pro
Scopes/Lenses: Main/Orion 80mm, DSLR/Tamron 18-400mm lens, guide/ZWO-340A
Computer: ASIAir
Cameras: Canon T2i DSLR, ZWO120MM (guide)
Utility Software: iPolar (for Skyguider polar alignment), iCap, Explorestars, Canon EOS Utility
Image Processing Software: Photoshop

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