Rotator angle pre and post meridian flip

Perhaps it’s a silly question, but I’m doubting about the best approach to rotator angle.
First of all, I don’t want the rotator moving after Meridiam flip, as if it turns 180º I should need different Flats for pre and post meridian images.

Using Sky-PA
When I define a sequence, or in a mosaic, I define usually the rotation angle in a PRE meridian position.
For example 30º.
After the meridian flip, if I uncheck “Maintain the object orientation”, Voyager knows I don’t want to move the rotator, and the solved Sky-PA should be 210º without moving the rotator.
As expected, the image result should be 180º flipped, but the flats should be the same.

That’s OK

But what happens If I begin the sequence and the object first image is taken AFTER the Meridian flip?
For example, in a second night, I begin later and the object has already passed the Meridian…
Is there a system Flag that makes voyager know that instead of 30º it must look for 210º?
Or is it going to Sky-PA 30º?? If it goes to 30º AFTER the Meridian, the rotator will turn 180º and the flats will be different.

If I use Rotator-PA
The question is the same.

If for the explained Sky-PA 30º my Rotator-PA is, for example, 45º, and I begin BEFORE the Meridian flip, there is no problem.
Voyager calculates the Off-set (15º) and for a solved Sky-PA of 30º, the Rotator-PA should be 45º.
After the meridian flip, I think it calculates 210-180, and doesn’t move the rotator.

But what happens if I begin the session AFTER the Meridian flip? It will try to maintain the off-set and will go to 30º after the Meridian instead of going to 210º!. So it will turn the rotator PA to 30º.

Do you know what I mean?
It’s very difficult to explain.

What I mean is that perhaps it should be necessary to add two different angles into one sequence: Pre o post meridian. Or making a convention: The angle used is always Pre-meridian (if you want to forget about checking if the sequence is OK, without checking the object position).

If not, the sequence needs to be different if you begin it before or after the meridian because of the angle.

I’ll investigate the behaviour when I have no clouds and time!
Thank you

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Sky PA solve on the sky, same sky PA after meridian mean to rotate 180° (not Sky PA value but the rotator and this is automatically done with solve). If you dont ask to mantain same orientation to not rotate the rotator 180° will be added to SKY PA requested. Starting before or after is managed by sequence.

Rotator PA doesnt look on the solved PA so just ask to driver to position at angle requested. If you ask to mantain same orientation a 180° flip will be done. Starting before or after is managed by sequence.

All is tested and in use since months , but if you found something not work let we know.
Before try to understand if you need to reverse the rotator rotation (this depends on your telescope type).

I tried to read what you have wrote but I read some things not correct on how works for you the Sky PA and Rotator PA and I dont understand if you have a problem.

In case of problem with evidence use support.

All the best

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Hello Leonardo.

Sorry for the confusion.
Yes, I had some unexpected behaviour (images not flipped, and what is more strange, an angle that was no X or X+180).

Perhaps is related to my Lunatico Seletek Rotator: I fixed some limits in order not having problems with cables (between 110º and 250º is a forbidden area).

Anyway, I’ll try to contact you through Support. I have the logs files, the images taken etc.

In the meantime, if you want, you may close this threat.
Thank you

If you have limit in you rotator … you cannot use the Sky PA without know exactly relation between Sky PA and your Rotator PA. Voyager cannot have (and will not have) a limit concept so if ask rotator to go on a defined SKY PA the rotator must go or Voyager will receive an error. With Rotator PA you are free to avoid limit before start.

Having a rotator and such big limits is something really unusual.

Hi Leonardo.
I’m not sure if the standard rotator behaviour avoid turning and turning without limitation in one sense.

I don’t want the camera and filter wheel cables turning in circles like a solenoid.
(Sorry for the example image, but it’s for illustrating my thoughts).

If the rotator is at 0º, and I send the rotator to 75º, after to 180º, then to 300º, and I then to 110º, what the rotator is doing? Turning all the way and messing the cables?

I can not check it now because it’s a remote observatory at a second home, but I’ll check it as soon as I can.

That’s why I set the limits. For astronomy pictures, with 270º to 90º (180º amplitude), you got all the possible relative angles of an object.

Anyway, with Voyager Rotator PA, all is OK. It’s perfect. I only have to sync once the Rotator PA and the real Sky PA, and always use the Rotator PA. (I konw that really you don’t need to sync, just only knowing the offset between them, but It’s easier if the offset is near 0).

Thank you.

This is something to ask to the driver developer of your rotator (not in charge to Voyager). I absolutely hope they have write things in the right way. Usually all rotators manage thing in way to not twist the cable.

Hi Leo and Fernando,
I confirm my Gemini Integra RF85 rotator driver manages rotation turning sense to avoid cable issue, I dunno other products, but I think it is imperative feature in any rotator drivers.
Of course everything works well with SkyPA in my setup, my2cents.

Pegasus Falcon Rotator also manages the rotation direction and has a limit sensor to control direction of and limit of turn in either direction.

Thank you Francesco and George.
I’ll ask Jaime from Lunatico about Seletek driver!

Hello Fernando,

Jaime here…

Yes our driver won’t twist your cables - the rotation will never cross the “forbidden zone”.
If, however, you have defined a wide forbidden zone, (as you said, between 110º and 250º is a forbidden area), then any goto to that zone won’t complete. it will go to the allowed position closer to destination.

Hope this helps explain your situation… ?

Best regards,


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Thank for you answer Jaime … and welcome.

All the best

Thanks Leo,

I should have come earlier… :slight_smile:

See you around.