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G11 slewing past meridian pointing to the ground...


Steve Lang
 

Hey Tyler.


I experienced something very very very similar to Bob's problem from the
message with the subject "Slew Errors #EXOS2 #ExploreStars" but with my
PMC-8 G11 a few nights ago.

- I have Lat/Long set right, been using the current setup for over a
year now (I am in Southern Hemisphere)
- Haven't yet tried an automated meridian flip, but slewing to targets
either side of the meridian has been working fine so far
- I use NINA (1.10, with hot fix #1), PHD2, Ascom 6.4SP1, latest release
Ascom driver and latest mount firmware
- PA was good enough - G11 on tripod but in observatory so haven't had
to revisit that in a long time

I was locating Cat's Paw Neb (RA 17:20:50.89, -36d 06'54.0", which at
that time was very high (Az/Alt: +288d 44'53.9" /+87d 48'36.7"). Used
NINA to platesolve, sync, move etc. Usual stuff that has been working
well for me, and the same as what I used to do with APT (which Bob used).

What seemed to happen is that the mount didn't get close enough first
time (not surprising, I had re-balanced and loosened clutches etc.),
platesolved, sync'd with mount driver, then tried to make a slight
adjustment then slew to a better place.

It seems that the scope was originally on the wrong side of the
meridian, and needed to re-slew was across the meridian. It started this
process by rotating the scope around DEC towards the ground! Luckily I
was in the obs, and hit the panic (power) switch before the cables were
tangled around the mount. It was a close thing, quite disconcerting.
Very much so, has dented my trust.


The reason I mention the link to Bob's message ("Slew Errors #EXOS2
#ExploreStars") as it seems very similar. Close to meridian (in my case
zenith), platesove (which would normally send a sync to the mount), then
an instruction to move to a new place. In both our cases, it seems like
the mount rotated (DEC)

Now I haven't yet managed to get any debug logs from ascom or NINA that
relate to this (not sure I can...) and I'm not keen to repeat the
exercise. Unlike in Bob's case, I'm sure all my software settings are
fine, but the solve/sync near zenith, followed by a move to a new
absolute co-ordinate seems to have been problematic at this time.

I've had no problems like this in the past at all that I can remember.

Any idea what might have gone wrong? Could it be a bug/condition that I
triggered (because I'm in southern hemisphere)?


Cheers -




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--
*Mounts:* ES PMC-8 G11, Orion Atlas
*Scopes:* ES FCD100-80, GSO RC8, Orion XT10i
*Cameras:* QHY 8L, QHY163m, QHY5L-II, Polemaster
*Misc:* QHY FW, OAG
*Software:* NINA, PixInsight


Jerry Hubbell - Explore Scientific VP Engineering
 

On Sat, Sep 5, 2020 at 07:51 PM, Steve Lang wrote:
I've had no problems like this in the past at all that I can remember.

Any idea what might have gone wrong? Could it be a bug/condition that I
triggered (because I'm in southern hemisphere)?
Wes emailed about this, here is how I responded:
 
"The problem is not the meridian flip done at zenith. All the mount cares about is what side of the meridian it is on, it doesn’t give a hoot about where DEC is. The problem here is related to the plate solve when near the meridian.

I have talked about this at least 2 times in the forum when people run into it. What happens is that if you are near the meridian and the mount is slewed to an object which the mount thinks is currently on the east of the meridian (which it is). You take an image of the sky, and the pointing is off enough where the current position is west of the meridian. The pointing was off enough from where the mount thought it was. In this case, as soon as you do a plate solve and a SYNC, you now tell the mount, “hey, you are actually west of the meridian!” and calculates the motor counts according to that position. The problem is created at that point.

The calculation of the motor counts depends on which side of the meridian you are on of course for both RA and DEC. So now the mount is 180-deg out of phase (the motor counts) so when you go to slew to the object again, it will point the mount to the ground.  My advise on the forum is to never do an initial plate solve on an object within 10 arc-minutes of the Meridian.

You must make sure that any object you are pointed at in the sky and you have photographed is actually on the side of the Meridian that the telescope is pointed at before doing a SYNC."

--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

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
Mounts
: 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!


Steve Lang
 

Hey Jerry.

Thanks for the detailed explanation.

Cheers -


On 6/09/20 2:47 pm, Jerry Hubbell - Explore Scientific VP Engineering wrote:
On Sat, Sep 5, 2020 at 07:51 PM, Steve Lang wrote:
I've had no problems like this in the past at all that I can remember.

Any idea what might have gone wrong? Could it be a bug/condition that I
triggered (because I'm in southern hemisphere)?
Wes emailed about this, here is how I responded:
 
"The problem is not the meridian flip done at zenith. All the mount cares about is what side of the meridian it is on, it doesn’t give a hoot about where DEC is. The problem here is related to the plate solve when near the meridian.

I have talked about this at least 2 times in the forum when people run into it. What happens is that if you are near the meridian and the mount is slewed to an object which the mount thinks is currently on the east of the meridian (which it is). You take an image of the sky, and the pointing is off enough where the current position is west of the meridian. The pointing was off enough from where the mount thought it was. In this case, as soon as you do a plate solve and a SYNC, you now tell the mount, “hey, you are actually west of the meridian!” and calculates the motor counts according to that position. The problem is created at that point.

The calculation of the motor counts depends on which side of the meridian you are on of course for both RA and DEC. So now the mount is 180-deg out of phase (the motor counts) so when you go to slew to the object again, it will point the mount to the ground.  My advise on the forum is to never do an initial plate solve on an object within 10 arc-minutes of the Meridian.

You must make sure that any object you are pointed at in the sky and you have photographed is actually on the side of the Meridian that the telescope is pointed at before doing a SYNC."

--
Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at explorescientific.com

www.explorescientificusa.com
1010 S. 48th Street
Springdale, AR 72762
1-866-252-3811

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
Mounts
: 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!

This email has been filtered by SMX. For more information visit smxemail.com

--
Mounts: ES PMC-8 G11, Orion Atlas
Scopes: ES FCD100-80, GSO RC8, Orion XT10i
Cameras: QHY 8L, QHY163m, QHY5L-II, Polemaster
Misc: QHY FW, OAG
Software: NINA, PixInsight