New PCM-8 Upgrade testing

Randy OConnell

I am just starting to test my new PCM-8 today (G-11 upgraded model).  How does the mount decide where the park position is?  Can it be adjusted?

Also, what is the procedure for aligning the mount during the day (for solar observing)? I've got other questions too.


W. Christopher Moses

I hope Jerry will correct me if I'm wrong:

Park position appears to be wherever the mount is when you power-up the pmc-8. My previous mount (Ieq45) was also like this. It was a PITA. But, with the G-11's built-in levels on the RA and DEC, I have found it to be really easy.
If you are in an observatory I could see the use of having a park position that is different than the zero position. If not, whatt, exactly is the goal? (Really, I'm asking - maybe I can write a quick program to do it) 

I've been meaning to get a solar filter. (We have to do something during the days, lol) Come to think of it, I'm not sure I know how to switch to solar tracking. However, I do think the sun is an option in ExploreStars. I assume selecting and slewing to it would change the tracking rate accordingly


Hi Randy, 

The programmed park position for the PMC-Eight G11 and EXOS 2 mounts is at the North Celestial Pole (NCP). This is the zero (0) count position of the motors and the scaling calculation in the ASCOM driver and ExploreStars application are based on this reference position. If you have physically positioned your mount to any other position than the NCP as Chris suggests, the pointing will not be accurate. ASCOM defines two positions that are similar, PARK and HOME. HOME is typically used in conjunction with an external sensor for a built in reference position. PARK is used as a user defined position.

In the current version of the ASCOM driver, the HOME position is the same as PARK and is not user configurable, although there is a way around this. This is typically found in a permanent observatory setting, and I use this technique in the remote observatory I manage. You can position the mount in any orientation that you wish and then turn tracking off. This is similar to telling the mount to go to a user defined position. Once you do that you MUST LEAVE THE PMC-Eight POWER ON to retain the current position.

Currently in the firmware, the motor positions are not stored in the non-volatile memory space. We have that on the list of updates to the firmware, and would not be a big amount of work to incorporate that.

Give me some time and I will get that incorporated along with a few other updates.

Randy OConnell

Thanks Jerry,

I did touch base with Scott yesterday and he filled me in on a few things.  I am still having a few issues and am a bit perplexed.  at one point when I went to park the scope ended up in a unusual position.  I am thinking that maybe I rebooted the PMC8, and didn't have the mount positioned in the park position.  

I have the mount oriented towards North and the GPS on my surface is on and updating the mount with the proper location.  For some reason when i would try and do an alignment, the some of the alignment stars that would be selected were below the horizon.  Unfortunately I had set my mount up behind the house (south side), so some of the northern stars were obstructed.  (it doesn't help that I tend to be solar oriented, and my star locating skills leave a lot to be desired).  

My problem is that when even selecting and alignment star (like Vega or Spica), when slewed to it, the scope would be no where near the the star.  At that point I wasn't sure if I should loosen the mount and manually adjust it, or try and drive it to the star.  Any suggestions?  BTW, when I ran the mount using the original drive system, I could do a North alignment, and set on the sun, and it would stay linked up for most of the day.  I believe I should be able to do the same with the new drive.


W. Christopher Moses

It sounds, to me, like one of two things: either your zero position was inaccurate or your location was not set correctly.

You can test the zero position by parking the scope. If it doesn't go back to a "straight up and down" position, and the bubble levels on the RA and DEC aren't level, then your zero position is off.  Just loosen the clutches and adjust it, while parked.

I would double check your location manually. Click on the icon in the upper left and select settings.

W. Christopher Moses

If you are doing things remotely, the other ideas don't work, or you just want another method, you could use Astrotortilla (or SGP, or TheSkyX) to do a plate-solve and sync.