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Re:Figuring out a meridian flip?

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In the simplest explanation possible, please help me to understand when I need to do a meridian flip and how to set it in Ekos so it happens when it's needed. I watched the module video but am still confused. Thank you.
Equipment: Skywatcher HEQ5 - Stellarvue 80mm access - Canon 6D (unmodified) - Stellarvue 50mm Guide Scope - ZWO ASI290MM Mini - Rasp Pi4
4 years 6 days ago #50986

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OK, I'll take a stab at it to start you off.

I believe your Skywatcher HEQ5 is a german equatorial mount (GEM). That is, you point it roughly at the north star when you set up (or at southern pole in the southern hemisphere). This process is called polar alignment and you need to learn to do that if you haven't already. For mounts like that, if you were to start tracking an object on the Eastern half of the sky, eventually it will cross the Meridian (though it's possible it will do that after dawn). In the northern hemisphere, the Meridian is the imaginary line running from the North Star heading towards the Southern Pole going through the Zenith, the high-point in the sky overhead. When your object crosses the Meridian, the front of your telescope will be pointing mostly up, and the back end where your camera is would be pointing mostly down (you have a refractor, so the camera is on the back end). After the object crosses the Meridian, your telescope, still tracking the object would start pointing at lower altitudes. The problem is, the back-end/camera would start going underneath your mount, into your tripod, and the camera will probably will hit something down there, causing the motion to stall, and potentially breaking or mis-aligning your mount, and certainly ruining your imaging session. To get around that, instead of continuing to track the object smoothly after the object crosses the Meridian, (usually after a little delay) the telescope switches to the other side of the mount (the back of your telescope would move to the east side, the front toward the west side), and as it tracks, now the bottom will be moving away from the tripod, instead of towards it. That switching of sides is called a Meridian Flip.

Jasem has posted a few videos on how to set up Ekos to do a Meridian Flip, e.g.
and there's plenty of discussion of it in the forum
and on YouTube and CloudyNights and elsewhere.
My 2 cents would be to simply check the box in the Mount tab which says "Flip if HA > ___" and fill in the value with something like 0.20 hours.
Start your imaging session. Use KStars or stellarium or other planitarium software to see if and when your object will be crossing the Meridian.
If it wil, don't trust the automated flip the first time, or until you've been successful with a few times. That is, instead be there watching/supervising it,
and be prepared to stop things if it looks like it going to crash, and/or if doesn't do the flip at all (and will eventually crash into the tripod).

When the session is running, while your object is East of the Meridian, the Indi Control Panel's mount tab, main control should indicate
"West (pointing East)", and after the flip it should say "East (Pointing West)". The Ekos mount tab should tell you how many hours and minutes
it is before the meridian flip will occur. If your mount is "West (Pointing East)" according to the Indi Control Panel, the mount tab it should NOT say Meridian Flip disabled.
You can also verify by eye that the telescope/mount is correctly labeled as "West (Pointing East)" or "East (Pointing West)".

Before you start, make sure your cables won't catch on anything, loosen the clutches and make sure the mount is able to move around freely then tighten them,
set up, and see if you can get the flip to succeed. It took me a while to get it to work reliably, but now I'd say it works pretty well.

This was all "off the cuff", please watch the videos to learn more, but you should be able to accomplish this.
The following user(s) said Thank You: Eric, Jose Corazon
4 years 6 days ago #50990

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Also, FWIW, here's a screenshot of my Ekos Mount Tab right now: photos.app.goo.gl/ieY2mLgo8j4MZR5q7
You can see that a Meridian Flip is planned in 46 minutes. Really, it should happen when the next image capture completes after 46 minutes.
You can see the hour angle (HA) is -34 minutes, which means, in 34 minutes the telescope will be pointing at the Meridian, but I've told it
to perform the flip 0.2 hours after that, so it won't flip for 46 minutes.
The following user(s) said Thank You: Eric, Martin
4 years 6 days ago #50991

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In the Mount tab, you can set at which time offset around the meridian you want the flip to occur, in RA hours.

If you want the mount flip to occur when the object you are tracking crossed the meridian half an hour ago, type 0.5 in.

It is important to remember that there is no "do a flip" procedure. Ekos will simply ask the mount to slew to the target again, and the mount driver will choose the right orientation based on the current object position in the sky.

Because the mount may not be perfectly polar aligned, or the geographical position may not be precise enough, it is important to provide a RA delay that is large enough. If it isn't, in the general case, Ekos would ask a slew but the mount would retain the original orientation per its own sidereal time calculation. Afterwards, no further slew would be requested and there would be a risk that the scope hit the pier.

-Eric
The following user(s) said Thank You: Martin
4 years 6 days ago #50993

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Still having issues with Meridian Flip. Left the scope running to capture 80 subs last night. When I got up this morning it had only captured 56. Looked outside to see the camera smashed into the mount and and a "click" "click" "click" sound coming from the mount. I am hoping it's ok I have not tested it yet.

I was shooting M63. While I was still up the HA reading as something like -00h 50m 10s. I checked the "Flip if HA" if more than 0.20 and selected the hour button. I thought I was all set to get some sleep and get my 80 subs but I guess not! Any ideas ANYONE what went wrong?
Equipment: Skywatcher HEQ5 - Stellarvue 80mm access - Canon 6D (unmodified) - Stellarvue 50mm Guide Scope - ZWO ASI290MM Mini - Rasp Pi4
3 years 11 months ago #52370

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A log might show but my guess is that the flip failed and the mount kept going until it found a hard stop. As for why the flip failed maybe the flip point is more than 0.2 hours past the meridian. It seems a lot though.
3 years 11 months ago #52372

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3 years 11 months ago #52373

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I'll look for the logs and try and post them.
Equipment: Skywatcher HEQ5 - Stellarvue 80mm access - Canon 6D (unmodified) - Stellarvue 50mm Guide Scope - ZWO ASI290MM Mini - Rasp Pi4
3 years 11 months ago #52376

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How do I figure out the flip point?
Equipment: Skywatcher HEQ5 - Stellarvue 80mm access - Canon 6D (unmodified) - Stellarvue 50mm Guide Scope - ZWO ASI290MM Mini - Rasp Pi4
3 years 11 months ago #52380

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You can do this manually, standing next to your telescope (that is, looking at it so you can see if it changes sides). Slew to a star that's a little before (east) of the meridian and plate-solve (align) so that you're reasonably confident about your position. One of he tabs in your mount's indi control panel should indicate "West pointing East" and you can look at your hour angle.. Now from there, slew to some position near there further west, just past the meridian. Does the mount stay on the same side? What is the hour angle now? If it didn't change sides, slew further to the west and repeat. Keep doing this until your mount decides to change sides and note the hour angle. This should give you a reasonable idea of how to set that hour-angle parameter on the Ekos "Flip if HA > " input box. Perhaps set it to a little more than that hour angles where your mount decided to flip (of course, make sure the scope wont be hitting your tripod at that hour angle).

You should make sure before you do all this that
- your computer's time is set properly to the local time,
- the entries in the indi control panel mount tab, "site management" sub tab seem right (e.g. for UTC time, UTC offset, latitude and longitude.
- You can park and slew properly -- e.g. when you start from a parked position and slew to some object, it points to within a few degrees of the object you wanted it to point to (e.g. it doesn't need to be exact, but shouldn't be e.g. 30-degrees off), and that it returns to pointing near the north star when you park.

Hy
3 years 11 months ago #52382

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I have been doing some experimenting with the meridian flip for the past few days. I have found that the meridian line on the Kstars map does not match the HA displayed in the Ekos telescope window. It can be a few minutes off. Also the telescope meridian flip point can be several degrees from the actual telescope meridian point and several degrees from the Kstars/Ekos meridian. To enable an automatic meridian flip, an object must be selected that is East of meridian for both the telescope mount and Ekos. And the flip is executed successfully only if the mount is West of the mount meridian point when the meridian flip goto command is sent to the mount.

Things to do to investigate the issue:
1) In Kstars select an object just East of the meridian line and note the HA time when that object actually crosses the line. HA = 0 is the reference time for the triggering of the goto command that causes the meridian flip. The goto command is sent to the mount when the HA>xx limit is reached.
2) Manually move the telescope with the hand controller or the Kstars telescope movement controls to the point where the counterweight bar is perfectly horizontal. The difference between the telescope location and the meridian line on the Kstars map can be determined by noting the RA position of the cursor on the map in the lower right corner of the map. This may not be the telescope meridian flip point.
3) To determine the telescope mount meridian flip point. select an object sufficiently far to the East that causes the mount to slew to that object with the telescope on the West side of the mount. Periodically press the Kstars goto button until the mount actually does the flip. Watch the HA position in the Ekos telescope window and note the HA position when the flip occurs.
3 years 10 months ago #53715

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What version of KStars are you using? Hy and I have been working on the meridian flip process recently and it will now retry if the flip falis. It also reports the pier side in the mount tab and can implement a HA limit that is intended to stop the mount tracking into the pier if it is in the wrong pointing state. This may all only be in the sources, not a released version at present. It all requires that the mount reports the pier side. If is doesn't none of this will be done.

in your section 2 some mounts report the mount axis positions. It may be worth watching the Ha or Ra axis position as the mount moves through the meridian. I would expect it to move through 180 or 0/360 degrees at that point. I would esxpect that the target pier side would change as the axis direction goes through 180 or 0.
3 years 10 months ago #53716

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