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Nexus II With Encoders Goes The Wrong Way But Changing + Or - Does Not Work Either (Solution: Use Alignment Stars As Far Apart As Practicable, But On The Same Side Of The Meridian - Read On!)

Losmandy G8 mount on loan to astronomy club equipped with a Nexus II/w encoders.  The instrument has been out of use for a time (pandemic), and we are trying to get it working again with Sky Safari Pro on an iPad.

last night, connect scope, realign on Arcturus, swing to Vega, the cursor lands fairly nearby.  Center the star in the scope, highlight it on the screen then hit align. The cursor goes to the star as it should.  But try another object and the cursor goes the wrong way.  Swing the scope, and the cursor is backward in Dec. Disconnect, go to settings and change the sign on the Dec axis (RA was positive 311296, Dec negative) go back, connect the scope, and it is still backwards???  We switched the sign back and forth several times, no change. 

So, perhaps we need to start a new alignment after swapping the sign, to clear things out.  We do that, and after re-align on Arcturus, everything is moving in the right direction.  Swing to Deneb, and the cursor, as with Vega before, moves near the target star.  Highlight the star, center it in the scope, hit align the cursor pops on the star.  Move the scope, and the cursor still moves in the right direction.  But, attempt another object, and Dec is again going backward and the cursor is well off a fairly nearby object in Dec.?

Driving home, I started to wonder if SkySafari’s location setting, clock or something like that is incorrect.  Not where I can check it now, but the sky displayed in the “now” setting, was certainly not alien to the time date, and location. 

We spent several hours screwing with this.  Flipping the scope around one side of the pier and then the other.  Removing the scope and turning the Dec around, an reinstalling the scope.  Nothing works.  

It seems odd that the cursor goes generally near the second-alignment star, but the separation between the stars in both cases is far greater in RA than Dec, so that explains that I suppose.  The key puzzling feature is swinging the scope sends the cursor in the correct direction until you have aligned with the second star and try to go somewhere else. 

Hope to go back up tomorrow night.  Hoping someone knows what the issue is, or has an idea.

Totally stumpted. 

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13 comments

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    Keiron Smith

    Bruce, 

    Please try controlling the Losmandy mount using a direct connection from SkySafari to SkyFi 3.

    Official Losmandy video is here: https://www.youtube.com/watch?v=trG71LhaM9s

    Nexus II is not officially supported.

    Thanks!

  • 0
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    Bruce

    This is a push to system, not a goto. Don't have skyfi3.  On closer inspection, this is what happens.  After the first star alignment the cursor moves with the scope as it should to the second star - almost perfectly on top of it.  But, when you go to align with the second star, you get an error notice (not consistently) that the scope is too far from the star and the cursor has jumped of to another location.  It is like the system has some kind of memory from an earlier alignment that overwrites the one-on process at the point of the second alignment.  Any help appreciated. 

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    Keiron Smith

    Please provide the following info:

    1. App and version.  See Help > scroll to the bottom.
    2. OS version.
    3. Device make and model.
    4. Any and all other hardware and software included in the configuration.
    5. Alignment process.
    6. Screenshot of the error message.

    Thanks!

     

  • 0
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    Bruce

    I have now run this on two different iPads with different Skysafari apps. An ancient iPad OS 10.3.3 with SkyS Pro 6.0.0.24, & a 6th generation iPad with OS 15.0.1 and SkyS Plus 6.8.5.2.  The setting circle system is a Nexus II unit hooked to a Losmandy G8 mount with the basic two-axis motor control for fine adjustment.  The scope is permanently mounted and well-aligned. 

    Since my original post, I have filtered out operator-caused confusion.  This is precisely the problem:  The first star aligns with no problem.  After the first star alignment, a test of the cursor motion shows it moves in the correct direction N,S,E and West with the movement of the scope.  Move the scope to the second star, and the cursor goes very near the second star as it should (photo 1).  But, after you highlight the second star (photo 2) and hit align, the cursor jumps off well away from the second alignment star (photo 3), and a message pops up that says the star is too far away (photo 4).  After that, The cursor now moves in the opposite direction that it should in Declination!

    Plainly, there is something that happens when the program calculates the alignment model that should move the cursor squarely onto the second alignment star, which is screwed up, sending the cursor off in the wrong direction and turning the model upside down from the north south perspective????? 

    I don't know the intricacies of this process, but I can't imagine how the interface between the Nexus system and Sky Safari can work while the scope is being moved from the first to the second star and then result in something so wrong after an align button is pushed.  That has to be something going on inside Skysafari, which I assume is the brains here, but why only my setup and with two different SkyS platforms?? It is a puzzle. 

     

  • 0
    Avatar
    Bruce

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    Bruce

    Above photos are in reverse order. 1st is at the bottom, showing how close the cursor is to the send star having originated with Arcturus. Next up it just before hitting align, third show the cursor position after hitting align and the fourth the error message. 

  • 0
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    Keiron Smith

    I found this regards the error message...

    SkySafari Error Message: "Your alignment target is too far from the telescope's actual position.  Please make sure you selected the right alignment target".

    Problem: Generally when you get this message, it means your initial alignment is not accurate.  When that far off, doing a local Align will not be able to correct the original alignment model. 

    Our rule for your scope type is that the object needs to be within 1º from where we think it should be based upon the alignment model in the mount.  If it is further than 1º away then there is probably some more serious problem; i.e:

    1. You have selected the wrong object to align on (e.g. you were centered on Jupiter but had some other object selected when tapping Align).
    2. The initial alignment model is very inaccurate.
    3. The time in the mount is different from the time in SkySafari.  A planet's RA/Dec is dependent on the time (unlike stars) so this error would really only happen with solar system objects.

    When you tap the Align button, we store an offset from where the mount thinks it is pointing to where you are saying it is pointing.  We apply that offset when doing GoTo or when showing the scopes reported location on the screen.  It has been our experience that if the offset is greater than 1º then this doesn't work well.

    Solution: Align again, with a detailed focus on accuracy.

  • 0
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    Bruce

    Thanks, but I don't think you are following the problem here, or I don't understand the system I have at all.  This is a simple push to mount with digital setting circles.  I don't think the mount has a time or a model in it at all.  It is dumb as a post.  I think all it does is convey movement to sky safari based on it's encoders.  I am very carefully selecting an obvious star as the first alignment star.  In this case, Arcturus.  When I hit align it asks if I want to align on Arcturus.  My assumption is that begins the model, and the model is in Sky Safari based on time, location, and an assumption that the mount is polar aligned.  I push the scope to the second star and the cursor goes quite close, suggesting that things are working properly and the model based on the first star is not too far off.  But, when I attempt to align with the second star the cursor does not go to that star, nor does it stay where it was.  It leaps off to somewhere else, and the north-south flip takes place so that now moving the scope south moves the cursor north and visa versa.  

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    Keiron Smith

    You have said, previously...

    The scope is permanently mounted and well-aligned. 

    What do you mean by "well-aligned"?

    Also, I found this on CN.

    Once switched on the Nexus II creates its own little Wi-Fi network. With your smart device you connect to the Nexus network then once Sky Safari is opened and configured to the network’s IP settings, you click “Connect” and when you move the scope you will see the target on your device’s screen move. In my case, the first time I used it, when I moved the scope up the target would move down. I then simply had to change the Sky Safari encoder settings for the “Alt” axis from “+” to “-“ at which point it moved in sync with the scope in both directions.  You then go through the Sky Safari alignment process and you’re in business for the evening.

    https://www.cloudynights.com/articles/cat/user-reviews/nexus-ii-review-r3255

     

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    Bruce

    I spend an evening carefully polar aligning the mount using the drift method.  I am well aware of the + - deal.  Those are set correctly, and the cursor moves in the correct direction, until after the attempt to align with the second star, when it flips.  Let me ask this.  I am crossing the meridian when going from star 1 to star 2. That introduces additional errors.  You say the program will reject anything off by more that 1 degree when aligning with the second star.  It is close, but looking at the image, it is not that close to the 2nd star.  Is it possible that a failed seconds star alignment (due to not being close enough) would cause the system to invert north and south?  It also occurs to me that the cursor running off to another location may also just be a consequence of the failed alignment and not indicative of a modeling error. Second question, how far should I attempt to separate the 1st and 2nd star.  I may try avoiding a meridian flip.  

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    Keiron Smith

    I think...

    I spend an evening carefully polar aligning the mount using the drift method

    Ensure your polar alignment is rock solid, as the SkySafari error message is indicating this is where the problem is.  The issue may be somewhere else, but taking the message a face value, the initial alignment should be the first place to look.

    I may try avoiding a meridian flip.  

    Excellent idea.

    I did find elsewhere, you should not pick two stars to align on that were very close together in RA.  SkySafari cannot build a good alignment model  like that.

    Sorry, I don't know if, but also I don't think that, the alignment failure is related to the inverted direction.

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    Bruce

    Resolved.  The one-degree tolerance was the information I needed.  A Meridian flip with a GE mount brings in extra errors.  In the interest of getting a wide spread between the alignment stars, I have been crossing the meridian.  Perhaps not a problem with an Alt/Az mount - the typical push to - but with my GE mount it was causing the alignment failure.  The relocation of the cursor after the second star alignment attempt was not the result of some spurious calculation process, but just SS throwing its hands up - essentially saying, I don't know where I am.  Also, having flipped, and not knowing where it is, the North-South inversion appears to take place.  

    The moral of the story is, if using a GE push to mount, stick with alignment stars as far apart as practicable, but on the same side of the meridian.    

  • 0
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    Keiron Smith

    An excellent result, Bruce!

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