Meridian flip script operational

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JohanB
Posts: 267
Joined: Thu Apr 21, 2016 5:55 pm

Meridian flip script operational

Post by JohanB »

Hi all,

Attached you'll find a script for executing a Meridian flip that has been tested under the sky on a number of occasions and can be tested yourself with the simulators first, before you run it on the real mount. Prerequisites for running the script are that you run AT, AI and AG V4.0_580 or higher, with the Astrometry Agent driver installed, configured and running. The script will wait for the mount to go 20min over the meridian, flip the mount, plate solve, recalibrate and start the guider and resume the AI sequence.

In order to get good results regarding framing after the flip, the mount should be plate solved and synced & centered with the new server based Astrometry Server before the flip, since Astrometry Server is the method of plate solve that is used after the flip. If you use the web service or the local Mac plate solver before the flip, framing may be off a bit.

An example of the framing after the flip is shown here, where i rotated the first sub after the flip 180 degrees and and superimposed it over the last sub before the flip. Apart from a little rotation that cannot be avoided, the framing after the flip is near perfect.

Screenshot 2021-03-06 at 23.41.58.png
Screenshot 2021-03-06 at 23.41.58.png (740.56 KiB) Viewed 414 times
More information on using the script is in the headers of the script itself, including the instructions for running it with the simulators. Please let me know if it works for you! When you run it on an RPi and you want to inspect the log, you can use "tail -f /var/log/syslog | grep Meridian" to single out the meridian flip related messages from the syslog.

Regards, Johan
Execute_Meridian_Flip.js
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Last edited by JohanB on Sat Mar 13, 2021 8:35 am, edited 1 time in total.
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Peter Polakovic
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Re: Meridian flip script operational

Post by Peter Polakovic »

:thumbsup:
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aaron
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Location: Upstate New York, US
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Re: Meridian flip script operational

Post by aaron »

Looking forward to trying this out!

One thing that confuses me:
The script will wait for the mount to go 20min over the meridian,
If my scope will hit my mount about 15 minutes BEFORE the meridian. Is this value customizable?
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aaron
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Re: Meridian flip script operational

Post by aaron »

Ah, I found you had previously answered this same question here: https://bb.cloudmakers.eu/viewtopic.php?p=4156#p4156. I'll give that a try.
JohanB
Posts: 267
Joined: Thu Apr 21, 2016 5:55 pm

Re: Meridian flip script operational

Post by JohanB »

Hi Aaron,

I initiate the flip by doing a goto to the current object. If my AZ-EQ6 is over the meridian it will flip on the goto. I found however that when i plate solve and sync AT, AT has different coordinates than the mount. In my case (because of the sloppy way i set up my mount), after the first slew and sync, AT is most of the times 10-12min ahead in RA compared to the raw mount RA coordinates. If do the goto when the AT RA coordinates are over the meridian, the mount will most likely just slew to the same object without flipping, because the raw mount RA coordinates may still be 23:59. So for my case i added a margin to let the RA coordinates be 12 min over the meridian before i do the goto, to make sure the mount RA coordinate is over the meridian as well. (just noticed i decreased the margin from 20 to to 12min in the final script).

In order to change it, to have to modify line 103;

from -> if ( east_of_pier && hour_angle > 0.2 && hour_angle < 12 && !flip_in_progress)
to something like -> if ( east_of_pier && hour_angle > 23.75 && !flip_in_progress)

If the condition is true, the function under this line will initiate the goto (in line 113). The big question is, whether your mount will flip when the goto is done 15 min before the mount has crossed the meridian. In the script i rely on the Skywatcher mont firmware to flip when a goto is done to an object over the meridian. Not sure how this must work in your case....

How do you normally flip when you're 15min before the meridian?

Regards, Johan
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aaron
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Location: Upstate New York, US
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Re: Meridian flip script operational

Post by aaron »

Thanks as always for your reply, Johan.

Currently I slew to some star on the far side of the meridian, then wait for 20 minutes or so, then begin plate solving, etc. It is boring, and there may be smarter alternatives. But I haven’t tried alternatives.

Maybe there is some bring basic that I’m missing...
JohanB
Posts: 267
Joined: Thu Apr 21, 2016 5:55 pm

Re: Meridian flip script operational

Post by JohanB »

Hi Aaron,

Not sure how to flip when the mount is still before the meridian. But we could automate your procedure. Store the target position, stop tracking, guiding and imaging when 20 min before the meridian, fire off a timer to wait for 20min and do the goto when the timer wakes.That shouldn't be too hard; can make a POC if you like. Do you use the mount synscan driver to drive the mount?

The good thing is that it can all be tested beforehand with the simulators. Would watch it in person the first few times though :-D

Regards, Johan
JohanB
Posts: 267
Joined: Thu Apr 21, 2016 5:55 pm

Re: Meridian flip script operational

Post by JohanB »

BTW Aaron, did you ever think of a vertical pier to just avoid the risk of mount collision, like this one; https://www.robtics.nl/nl/zuilen/1844-s ... ingen.html
iMustBcrazy
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Re: Meridian flip script operational

Post by iMustBcrazy »

Thanks for the script! I'll give it a try as soon as I can :)
JohanB
Posts: 267
Joined: Thu Apr 21, 2016 5:55 pm

Re: Meridian flip script operational

Post by JohanB »

Great, let me know if there are issues!
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