Re: Mount moves off Target

Steve Lang


I have noticed something similar a few (maybe 3-4) times. I have not been able to reproduce and I do not know what specifically caused it. It may not be the same problem as yours, but I will describe it here.

I use the G11 PMC-8 for astrophotography only and use NINA for capture and control, with PHD2 for tracking, both via. POTH. When I have seen it, it seems to track at something like twice the normal speed. It keeps going and keeps going. The only way I can stop it (and I only found this the last time) was to hit the 'stop' button on NINA scope control screen. This seems to make it reset to normal sidereal tracking.

I had not determined whether or not it was a NINA error, PMC-8 error or something else - I just don't know. I've seen the same thing enough times for it to be annoying, but have no further details, nor logs. I was going to turn on ascom debugging/trace or something so if it popped up again, I might have some useful logs.

Interestingly, I was going to run the Ascom conformance tool next time to check general conformance, but this seemed to be very much an edge case problem for me.

Cheers -

On 1/03/20 10:52 am, Jerry Hubbell - Explore Scientific VP Engineering wrote:
On Sat, Feb 29, 2020 at 04:38 PM, Robert Spellman wrote:
After tracking well sometimes for over an hour the mount suddenly moves off target ( not auto guiding just viewing), I cad bring it back with the pad command sometimes it resumes tracking sometimes it just keeps drifting
Hi Robert,

I assume you are using the Explore Stars application when this occurs. The way Explore Stars works in POINT mode is that it is continuously sending commands to move to the calculated position based on the RADEC coordinates of the object adjusted for the mount model set during the alignment routines. If the mount loses communications with the tablet, it should track at the last set rate which should be very close to the sidereal tracking rate. When you manually position the mount using the direction buttons, it goes into TRACK mode where the rate is fixed at the Sidereal rate. I am at a loss to understand why the PMC-Eight would stop tracking completely, perhaps it is not.

I assumed that when you said the mount moves off target that it had stopped tracking completely. How fast does the mount move off the target when this happens?  Have you seen this behavior (loss of tracking) when in TRACK mode? 

The only other thing it could be, and this may be the case, is that if the PMC-Eight loses communications completely with the tablet, after 20 seconds the mount will stop moving. This behavior is designed into the mount system. You can install a version of the firmware that we have available on our website that disables this function and allows the mount to keep tracking when not connected to the tablet. When the tablet reconnects, it will update the information on the tablet and continue to operate. 
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!

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