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UC22 and Argo Navis for imaging

 

Hi all,
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There is a guy on Astrobin who mentioned he will try deep sky imaging with his Obsession UC22 and AN using NINA. I mentioned this group in case he needs help.
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So I became curious how the DSC and ServoCAT actually works.
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In the case of AN i assume one has to do the 2-star alignment with the handpad/AN unit and not remote?
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Then connect to the Ascom ServoCAT driver.. does the Meade Generic driver work with AN?
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When sending a slew command this goes directly to ServoCAT without any "interference" from AN?
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When platesolving in a capture software and the scope needs to move a specific distance, the ServoCAT understands the distance without help from the DSC?
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In my case with Nexus DSC Pro if I understand things correctly it does not allow a command to just pass through to ServoCAT so instead it "pretends" to be (emulates) ServoCAT and translates the first slew and platesolve + sync as the first star in the 2-star alignment, and second star with the second platesolve + sync.
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So all commands are sent from Nexus to ServoCAT, in other words ServoCAT has no idea that the Meade Gneric driver is behind the wheel operating Nexus?
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Clear skies
Gabriel?
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*** (section break, to help avoid confusion)
For the following, one is connected to the Nexus DSC through their computer, using the LX200 driver:
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The first two align points sent to Nexus DSC (Pro or not) are treated as the two alignment points.? It is advisable to have done the alt ref beforehand.? Treat these first two align points as you would when doing the alignment with the panel (the actual keypad of the Nexus DSC body) - far away enough, backlashes cleared, ... .
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Every align point sent after those first two is treated as a local sync in Nexus DSC.? If you so choose, you can use those additional syncs to develop an MPoint model.
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It does not matter you you obtain those syncs, i.e.: actually centering things yourself and pushing a sync button; or, through plate solving then syncing.
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You can run this programmatically, eventually.? There are two hiccups with the latest Nexus DSC Pro firmware I received, which is far ahead of the firmware available on the site.? For starters, the Nexus DSC Pro is sending out the wrong latitude and longitude, but it's a simple formatting error, so that should be fixed easily.? The lat/lon is rather necessary to do this programmatically, if you know where the trees are, for example.? You would go to where the trees aren't, then solve and sync there.? But the gotos are in RA/Dec, so you need the lat/lon/time to get the proper RA/Dec to send it to, from the alt/az where the trees aren't.? The second hiccup is that it doesn't align when the first alignment point is between zenith and the celestial pole (I'm in the Northern hemisphere).? This will be harder to deal with fixing, but the workaround is to slew to the South first, then start from there.? It just adds the time it takes to slew from my park position (toward North) to the South.
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Gotos are sent to Nexus DSC, which passes it along to ServoCAT through the USB cable.? ServoCAT then talks to the DSCs for the refinement, as usual.
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For the following, one is connected to the ServoCAT through their computer, using Hilios' driver, for example:
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A sync is just a local sync sent to the ServoCAT itself.? Nexus DSC does not see the sync at all.? Gotos are sent directly to ServoCAT.? ServoCAT then talks to the DSCs for the refinement, as usual.
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When connected to ArgoNavis from the computer, none of the above is possible.? One can't align from the computer with an ArgoNavis, and one can't send gotos from the computer with an ArgoNavis.? I never connect to the ArgoNavis through ascom or the like, for any sort of control (because there is none); simply to update elements for comets, asteroids, and satellites in ArgoNavis itself.? One MUST be on "From Planetarium" in ArgoNavis, even when connected to ServoCAT from a computer, otherwise the goto is to whatever is on ArgoNavis' screen.? The tracking rate is always sidereal when on "From Planetarium", as it's just coordinates, rather than an object.? If your computer tells ServoCAT to goto M51, but ArgoNavis' screen is on Moon, it will go to the Moon, and track at lunar.
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In practice, I use Nexus DSC Pro, so I can do an alignment programmatically, without having to center stars myself.? Once I do an alignment programmatically, through platesolving (being mindful of the wrong lat/lon), I switch the connection to ServoCAT from the computer.? There is nothing left to do with NexusDSC from the computer really, so I may as well go straight to ServoCAT.? It doesn't really matter though, so dealer's choice there.? I only use an ArgoNavis when I specifically need some function that Nexus DSC and ServoCAT together can't provide.? At the moment, that's only satellite tracking, but then I am forced to center stars myself.
 

Thank you Sevan!
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I use the latest Meade Generic driver.
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Serge sent me a firmware version for Nexus DSC Pro that fixes the lat/long issue. After that it reported the correct lat/long every session. It was a bug causing the issue he said.
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Strange with the alignment... i have always done the 2-star remotley starting at 30 AZ and 65 Alt then 135 Az 70 Alt. Points and tracks well. (i live 63 degrees north). My alt ref is 0 Az 63 Alt, i platesolved the position one session and then i made markings on the scope so i just position the scope, start everything up and walk inside then everything can be done from the house.
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I have created a 2-star alignment sequence in NINA so it is fully automated provided the settle time is 60s, to speed things up i am hands on and check what the guidecamera is seeing so the scope has settled, then platesolve and sync. Since 60s is "just to be sure".
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The only thing standing in the way of full automated imaging all night long, is that sometimes after a GoTo/Slew/Recenter the scope slews away as if the backlash has not been cleared, if i quickly slew in the opposite direction with NINAS virtual handpad which offers slowmotion control then the scope stops and tracks as it should.
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I am not sure what is going on since after a GoTo ServoCATs last move is supposed to be sidereal, also this issue does not always occur.
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In the beginning of a session this is not a problem since i am hands on anyway, and i enjoy that. But if i need some sleep and the scope has drifted NINA has a function called "Center after drift" which works by detecting drift, so if i set 3 arc minutes it will automatically slew and center untill it's within 3 arc minutes again. The problem though, is that after slewing back within 3 arc minutes, even though the correction is so minor the scope starts moving away which causes center after drift to fail.
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I wrote about this in the Meade Generic driver discord and CJdawson (spelling?) was not aware of any slewing issue in the new drivers but suggested i used ascom tracelog to see what was going on, i can't do this now though since the season here has ended, would be nice to solve this problem for the coming season!
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/Gabriel
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On Fri, May 16, 2025 at 01:12 PM, Gabriel Wiklund wrote:
sometimes after a GoTo/Slew/Recenter the scope slews away as if the backlash has not been cleared
I get that too, from time to time, even with an ArgoNavis.? I have reason to believe it's just a timing issue with ServoCAT talking to the DSCs.? ArgoNavis gives beeps indicating when the slew is "done", after ServoCAT having done the talking to the DSCs thing and recentering.? ServoCAT still moves along with that beep from time to time, and less often, after the beep.? Highly intermittent, and I have found nothing making it more likely than not to happen.? On one night, and one night only, I had it happen a few times, so I unplugged and re-plugged the serial connections on the SC and the AN, and it went away.? That's not enough to say it's related, but maybe perhaps?
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That this doesn't happen with slews, but only with gotos, is what makes me believe it's a timing issues.? With a slew, there is no talking to the DSCs for refinement.? You could try just letting PHD2 take care of it, which only slews rather than sending gotos, but the issue is that with PHD2 and alt/az, you need to recalibrate every so often as the parallactic angles changes - the camera chips are rotating relative to the sky as the scope tracks.
 

In NINA there is something called "Slew to RA/DEC" or "Slew to ALT/AZ". Does this still mean the Meade Generic driver is causing Nexus to send GoTos since Nexus can't "slew" only?
 

Sevan,

Just a clarification of what is going on. The "beep" is actually issued by the ServoCAT to the AN. It is indeed issued when the slew is finished. There is no motion after that, other than tracking which happens immediately, with 2 exceptions.?

1) the backlash is unresolved and indeed it isn't motion but the lack of motion (at the actual point of rotation - the bearing for ALT or the ground board for the AZ. Note that backlash isn't only there in the ServoCAT gearboxes but its also in the mechanics of the scope - which the ServoCAT has no measurement of nor any control over. So there are two sources of lash that need to be resolved. Even if LMIS is in play there still can be backlash seen.?

2) If AutoLOCK is on AND there is backlash there will be drift --- AL will ultimately bring the center point (where it was last left - whether through the results of a GOTO or if moved after that - its center) back to the center. Note that "center" in one persons eyes - depending on the angle they're looking at through the eyepiece isn't?necessarily?center for someone else... so "center" just means where it was left and where the ServoCAT believes that point to be.?

Additionally the update rate from the ServoCAT to the DSC is about 3X a second... so there's no "timing issues".?

Gary Myers
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------ Original Message ------
From "Sevan Aydin via groups.io" <sevan.aydin@...>
Date 5/18/2025 10:52:18 AM
Subject Re: [ServoCAT] UC22 and Argo Navis for imaging

On Fri, May 16, 2025 at 01:12 PM, Gabriel Wiklund wrote:
sometimes after a GoTo/Slew/Recenter the scope slews away as if the backlash has not been cleared
I get that too, from time to time, even with an ArgoNavis.? I have reason to believe it's just a timing issue with ServoCAT talking to the DSCs.? ArgoNavis gives beeps indicating when the slew is "done", after ServoCAT having done the talking to the DSCs thing and recentering.? ServoCAT still moves along with that beep from time to time, and less often, after the beep.? Highly intermittent, and I have found nothing making it more likely than not to happen.? On one night, and one night only, I had it happen a few times, so I unplugged and re-plugged the serial connections on the SC and the AN, and it went away.? That's not enough to say it's related, but maybe perhaps?
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That this doesn't happen with slews, but only with gotos, is what makes me believe it's a timing issues.? With a slew, there is no talking to the DSCs for refinement.? You could try just letting PHD2 take care of it, which only slews rather than sending gotos, but the issue is that with PHD2 and alt/az, you need to recalibrate every so often as the parallactic angles changes - the camera chips are rotating relative to the sky as the scope tracks.
 
Edited

PHD2 can measure Dec(alt) backlash which would include the whole system so if it's within 10 arc min i assume you could enter the precise measured value in ServoCAT sky.?
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I only have this issue in altitude, never in azimuth so I could leave azimuth alone.
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This means autoguiding will not work but I can do 10 seconds unguided. I say 10 seconds, because if I go shorter the frame download time for my DSLR will reduce actual imaging time.
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Does this mean that the GoTo will "stay" since the precise backlash for the whole system is set?
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Unfortunately I will not be able to test this before August.
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If this works then NINA will keep the object within 2-3 arc minutes of the center for the whole night.
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Or even change object every 1 hour to minimize field rotation then add exposure time in each object next clear night when in the same location in the sky, so you could get lots of Integration time and minimal crop of the corners for each object.
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/Gabriel?

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