Faulty iEXOS 100?



Last week I got the iEXOS 100. My Zenithstar 73 is too heavy to balance with my Baader diagonal and Hyperion Zoom eye piece so I have ordered an additional counterweight. In the meantime I have been experimenting by trying to align it without the diagonal or EP on the scope by just using my WO Red Dot Finder only.

Once the mount is perfectly balanced and the scope perfectly balanced and aligned perfectly aligned to Polaris, I plug the power in, hit reset alignment and then do a 3 star alignment. Note at this stage that I have selected iEXOS 100 within the ExploreStars app and my coordinates are super accurate. You can see there's an issue because it is way off when it gets to star 2 and still way off when it gets to star 3 during the alignment process. I am hitting sync and then enter after each alignment. Once the 3 star alignment is completed I ask the mount to slew back to Polaris and it is around 4 inches off when I look through the WO red dot finder.  I think I did the whole process from start to finish 4 times last night which included going right back to removing the mount to check the level of the tripod etc. I did notice that before taking it outside it would not fully return to Home on a few occasions after doing virtual alignments indoors so I do suspect a fault.

I'm going to give it one final try tonight before I through in the towel and arrange a return, but just wondered if anyone has any ideas please?

Jerry Hubbell - Explore Scientific VP Engineering

On Wed, May 6, 2020 at 08:06 AM, @StrangeDays wrote:
You can see there's an issue because it is way off when it gets to star 2 and still way off when it gets to star 3 during the alignment process. I am hitting sync and then enter after each alignment. Once the 3 star alignment is completed I ask the mount to slew back to Polaris and it is around 4 inches off when I look through the WO red dot finder. 

Hi Luke, welcome to the PMC-Eight forum, thank you for purchasing your mount.

First,  it is normal that when you perform a 2 or 3-star alignment that when you slew and have to center each star that each one will be off because the first part of the procedure is to record the offset for each star. There is no correction applied during this phase of the procedure so when it slews to each star they will be off. It is important to understand that even with a perfect "physical" Polar Alignment there are other errors causing the mount to not slew directly to the star including home position index errors (the little arrows on each axis defining home), Tripod/mount level error, and also Cone error. 

Now if you have an excellent Polar Alignment there is really no reason to perform a 2 or 3-star "virtual" alignment as typically if you have your tripod level, and little to no cone error a simple SYNC on a single star after slewing to it will get your mount synchronized to your mount. I am not sure what platform you are running ExploreStars on, but the term SYNC during a 2, or 3-star alignment is a bit of a misnomer in that all you are doing is ENTERING the star position into the alignment routine for subsequent use during the alignment model calculation. I think we have updated that button on the Android and iPadOS version of ExploreStars to say ENTER instead of SYNC. The SYNC term is really only used to reset the motor counts to the current "known" RADEC coordinates. 

Once you have completed the 2 or 3-star alignment as you describe and you try to slew to Polaris, you have to realize that that is a very difficult position to slew to when the values are being calculated through the alignment model. The RA values that are calculated via the alignment model transform can have quite a bit of error near the pole because of the trigonometric functions. You should only gauge the accuracy of the alignment model by slewing to other positions in the sky with DEC values < 80-degrees probably. Having said that, If you truly have an accurate "physical" polar alignment, you really do no need to perform a "virtual" polar alignment, just SYNC on a single star to align the mount to the sky as discussed before. 

I hope this clarifies what you are seeing.

Thanks again for joining the forum.
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

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!


Hi Jerry,

Thank you for your reply.

OK, I will disregard any accuracy during the alignment process going forward.

I did try to align to other objects including Venus which was low, but they were all out by a similar margin.

Please see screen grab below. I have been pressing SYNC on the right and then Enter on the left after each star. Is that correct?

A home position index error could be a factor. What procedure should I follow to check and fix this? One thing I did notice was that having physically aligned to Polaris before powering up the mount and immediately syncing Polaris in the app, the scope would move a little bit when I hit Park. I assumed it would stay still because by turning the app on with Polaris aligned it should register that as home and by immediately syncing that same location with Polaris without making any movements, the mount should see Polaris and Home as the same location.

The only other thing to report is that having centred Venus in my WO Red Dot I went inside for a cup of tea and on my return 15 minutes later Venus had drifted out from under the Red Dot. It was tracking it, just not very well.

Is there a chance I have a faulty unit? I think its a great mount so I really want this to be user error. What would you recommend I try tonight?

I didn't think there were any arrows on the axis of the iEXOS 100?

James Ball

Correct, not arrows on the iEXOS-100.  I made some using toothpicks, taping them to the separate parts so they span the silver spacer making it easier to align.  There is a procedure listed in the forum here somewhere that explains a way to use a simple bullet level to find exact polar home and works well.
James Ball
Dawson Springs, Ky
Mounts: iEXOS-100
Scopes: Meade ETX90RA(deforked now) Sky Watcher 150MCT
Camera: ZWO ASI 120MC-S
Software: Explore Stars Android, ASCOM, Stellarium Scope, Stellarium, AS!3, SharpCap, RegiStax6.