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Losmandy GM811 / Gemini 2
NINA

Last night was the first time I tracked an object through the meridian. I had NINA programmed to flip 5 minutes past the meridian, with a maximum of 10 minutes. Use pier side was ON.

I'm using a refractor, so my safety limits are:
EAST=94
WEST=95
WESTERN GOTO=0 (I think... I found it set to 0 but I had it set to 2.5 the last I looked)

The target crossed the meridian and when the exposure completed (I was using 8 minute exposures, so between zero and 8 minutes after meridian crossing), NINA said it was doing a meridian flip. All the steps completed and it re-centered and began tracking again. However, the meridian flip never actually occurred and a couple minutes later the scope tracked into the western limit and stopped. I backed it up manually, did another GOTO from NINA and it flipped and I continued imaging normally.

I am trying to figure out why the flip never actually occurred in spite of NINA saying it did. I assume NINA does a meridian flip simply by commanding a GOT and my guess is that the issue is my western safety limit in conjunction with the NINA settings?

If I am analyzing this correctly, with a western limit of 95, I have 20 minutes of tracking past the meridian before it tracks into the limit and stops. I have reconfigured NINA to perform a flip if the object is between 2 and 18 minutes past the meridian and I have left the western GOTO limit at 0. Am I correct in assuming that if an exposure finishes with the object between 5 and 18 minutes past the meridian, NINA will do a simple GOTO.... which should succeed because the object will be between 5 and 18 minutes past the meridian (with a western goto limit of zero)? And if an exposure finishes with the object at 4.9 minute past the meridian, NINA will begin a new exposure that will (with 8 minute exposures) leave the object at a max of 13 minutes past the meridian.... which will trigger a flip on completion?

Kinda makes my head explode ;)

Side question..... what is the easiest way to unlock the mount if it has hit the safety limit and stopped? Can this be done remotely or does it have to be at the HC? I went out to the scope and could not back it up with the HC. I had to do a PARK and then stop it part way. At that point it resumed tracking and responded to a SLEW from NINA. Since my target was now west of the meridian, the mount flipped and everyone was happy. Was there an easier way?

Paul


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Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

Hi Paul,

I can't validate the NINA logic, as I don't know what it does to perform a meridian flip. Maybe looking in some logs will tell you what and when it tried to do?

Gemini interprets Goto limit set to zero as the default, meaning 2.5 degrees before the safety limit. Maybe that's the reason the mount didn't flip.

Regards,

? ? -Paul

On 5/1/2021 10:46 AM, Paul Kanevsky wrote:

Gemini interprets Goto limit set to zero as the default, meaning 2.5 degrees before the safety limit. Maybe that's the reason the mount didn't flip.
Regards,
? ? -Paul

AH, I missed that the western GOTO limit is not degrees past CWD..... it is degrees EAST of western safety limit, right? That would explain it.

So with tracking = 0.25 degree/minute if I want the flip to occur at or after 5 minutes after meridian with a western safety limit of 95, I set the western GOTO limit in Gemini to "3:45". Did I get that right?

It is tricky working in minutes of time in NINA and degrees in Gemini ;)

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

On 5/1/2021 11:18 AM, Paul Goelz wrote:

So with tracking = 0.25 degree/minute if I want the flip to occur at or after 5 minutes after meridian with a western safety limit of 95, I set the western GOTO limit in Gemini to "3:45".? Did I get that right?

And a related question.... is there any reason not to simplify things and always set the western GOTO limit = western safety limit - 90? Ie., coincident with the meridian.

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

Yes, that's right: set the goto limit of 3.45 degrees before the safety limit.

Meridian flip is a function of a German Equatorial mount. Most people would prefer not to do a meridian flip. If you can get away with safety limits at 120 degrees or even more, then you can continue to image much longer on the same side of the meridian, possibly even avoiding a flip. It's a tradeoff between safety and convenience :)

Regards,

? ?-Paul

On 5/1/2021 11:57 AM, Paul Kanevsky wrote:

Meridian flip is a function of a German Equatorial mount. Most people would prefer not to do a meridian flip. If you can get away with safety limits at 120 degrees or even more, then you can continue to image much longer on the same side of the meridian, possibly even avoiding a flip. It's a tradeoff between safety and convenience :)

I used to image with an 8" SCT and my safety limits were WAY larger. But I am now using an AT115EDT refractor and with the camera hanging off the back and no pier extension, 95 is as good as it gets to the west for guaranteed clearance regardless of DEC. Maybe I need to look into a set of risers or a pier extension......

Too bad you can't set safety limits that take DEC into consideration. There is only a small range of DEC where the camera is likely to hit the tripod leg. But if I can get the meridian flip parameters figured out I guess it doesn't matter.

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

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On 5/1/2021 12:28 PM, Brian Valente wrote:

Regarding safety limits, you can set the more aggressively (larger) and take a chance that your DEC won't be in exactly the wrong place for a pier collision, but that seems like tempting fate

Since my scope is in the driveway in the dark and I'm in the house, I'm not comfortable just assuming it won't hit.

A pier extension is an inexpensive and easy option to increase your limits

Agreed. I'm just cheap so I'm waiting for a used one to turn up ;)

Paul


--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

--

Hi Paul,

I can't validate the NINA logic, as I don't know what it does to perform a meridian flip. Maybe looking in some logs will tell you what and when it tried to do?

Gemini interprets Goto limit set to zero as the default, meaning 2.5 degrees before the safety limit. Maybe that's the reason the mount didn't flip.

Regards,

? ? -Paul

OK, after posting on the discord and not getting a workable answer I think I figured it out for myself.? This is not a NINA or Gemini issue.? It is a misunderstanding of the settings and process on my part.? When NINA decides it is time for a meridian flip it does the flip simply by issuing a GOTO to the same target.? The reason my NINA flips were failing was because when NINA triggered a flip, the target was PAST the meridian but it was NOT past the western GOTO limit so the scope correctly decided the target was still reachable from the same side of the pier and the NINA's GOTO did not trigger the flip.? At that point, the flip has been triggered and failed and the mount will simply continue tracking until it hits the western safety limit.? Happened a couple times.??

After some head scratching and experimentation, I set my western GOTO limit equal to my western safety limit minus 90 (95-90=5 degrees in my case).? This causes Gemini to perform a meridian flip for any GOTO to a target any amount west of the meridian.? To prevent a race condition, I set NINA to trigger a flip one minute (0.25 degree) PAST the meridian.? Set this way, a flip is triggered when the current exposure ends with the object at least one minute past the meridian.? With the object one minute (or more) past the meridian, NINA issues a new GOTO which causes the scope to flip and Paul is a happy astronomer ;)??

The takeaway is to make sure that NINA is configured so that any flip is triggered with the object PAST the western GOTO limit but of course NOT past the western safety limit.? In my case, there is a 5 degree overlap (20 minutes) and since I never use more than a 10 minute exposure, a flip will always be triggered before the mount hits the western safety limit.??

Paul

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On 5/3/2021 3:03 PM, Brian Valente wrote:

FYI there are a couple different ways imaging programs attempt to initiate a meridian flip - one is issuing another goto to the target. the other is an explicit flip. different apps use different approaches. As if it wasn't already tricky enough

Yeah, that and the way the western GOTO is implemented were confusing me. Even harder that the mount takes input in degrees and NINA uses time before / after meridian. Frankly, I think this would be a lot simpler if Gemini simply used the actual meridian as the default meridian flip position without bothering with the western GOTO limit unless specifically needed.

It also didn't help that I had the location set incorrectly in Stellarium and that was causing a disagreement between Stellarium and Gemini about where the meridian was.....

I've asked before and I forget the answer.... if I track into the western limit and the mount stops, what is the easiest way to wake it back up so that it is responsive to slew commands and buttons without losing alignment? Or is alignment lost when tracking stops?

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

On Mon, May 3, 2021 at 05:01 PM, Paul Goelz wrote:

I've asked before and I forget the answer.... if I track into the
western limit and the mount stops, what is the easiest way to wake it
back up so that it is responsive to slew commands and buttons without
losing alignment? Or is alignment lost when tracking stops?

Alignment is not lost after safety limit stop. You can use the HC buttons at centering or slew speeds to back the mount out of the safety limit stop. In Gemini.NET driver you can also ask the driver to do this for you, automatically. Set near the bottom of safety limit configuration screen:



Regards,

? ?-Paul

On 5/4/2021 7:27 AM, Paul Kanevsky wrote:

On Mon, May 3, 2021 at 05:01 PM, Paul Goelz wrote:
I've asked before and I forget the answer.... if I track into the
western limit and the mount stops, what is the easiest way to wake it
back up so that it is responsive to slew commands and buttons without
losing alignment? Or is alignment lost when tracking stops?
Alignment is not lost after safety limit stop. You can use the HC buttons at centering or slew speeds to back the mount out of the safety limit stop. In Gemini.NET driver you can also ask the driver to do this for you, automatically. Set near the bottom of safety limit configuration screen:

Thanks for the explanation of the "nudge" checkbox. I assume with that checked, a slew will function normally even if the mount has hit the safety limit? So if I track an object until the western safety limit is reached and the mount stops, a subsequent slew to the same object will cause a flip and complete normally?

But FWIW, the last time I tracked into the safety limit after a failed NINA meridian flip, the HC buttons DID NOT work at slew speed. The only way I could get the mount responsive again was to initiate a PARK and then abort it after the mount started slewing. Did I miss something?

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

Try Centering speed to nudge the mount out. I forget, but it's likely that slew speed isn't supported when stopped at the safety limit.

Yes, when nudge option is turned on, Gemini.NET will simulate you pressing the HC buttons at centering speed to nudge the mount out of the safety limit, and then will issue the Goto command that you requested.?

Regards,

? ? ?-Paul

On 5/4/2021 7:27 AM, Paul Kanevsky wrote:

Alignment is not lost after safety limit stop. You can use the HC buttons at centering or slew speeds to back the mount out of the safety limit stop. In Gemini.NET driver you can also ask the driver to do this for you, automatically. Set near the bottom of safety limit configuration screen:

I had a look in Gemini.net and two questions came up....

1. When I check the "nudge" checkbox, I get a warning that I am disabling the Gemini built in slew disabling mechanism and do I want to do that. Does that mean that when the box is checked, after the western safety limit is reached a slew to an object past the western safety limit will now slew PAST the western safety limit if that box is checked? Or is the western safety limit a hard limit and only slews to the east will function?

2. I note that the in the safety limit settings section of the Gemini.net driver, the western GOTO limit is described as "degrees from CWD". Is that actually how the western GOTO limit is set in the driver? I have always understood the western GOTO limit to be degrees EAST of the western safety limit.

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

On Tue, May 4, 2021 at 08:07 AM, Paul Goelz wrote:

I had a look in Gemini.net and two questions came up....

1. When I check the "nudge" checkbox, I get a warning that I am
disabling the Gemini built in slew disabling mechanism and do I want to
do that. Does that mean that when the box is checked, after the western
safety limit is reached a slew to an object past the western safety
limit will now slew PAST the western safety limit if that box is
checked? Or is the western safety limit a hard limit and only slews to
the east will function?

2. I note that the in the safety limit settings section of the
Gemini.net driver, the western GOTO limit is described as "degrees from
CWD". Is that actually how the western GOTO limit is set in the driver?
I have always understood the western GOTO limit to be degrees EAST of
the western safety limit.

1: That warning is telling you that you're overriding the default behavior of Gemini once stopped at the safety limit. It doesn't override the safety limit. It will never slew past the safety limit.
2: That's a copy/paste error in the Goto limit label. I'll fix it :)

Regards,

? ? ?-Paul