Help please from users of Synscan 4

[MikeODay]

The Synscan 4 with my new mount ( EQ8 ) has strange behaviour and I am trying to find out if it is bug, a fault in the unit or a strange "feature" of the firmware.

During tracking in RA the celestial declination reported by the Synscan is slowly changing even though the declination axis of the mount is apparently not moving. 

Has anyone else noticed this?  If you get a chance could you check?

 

In my case the problem is seen via the following steps:

- start aligned scope from park
- select and rotate to object using Synscan 
- on hand controller display the rotation angle of the mount's declination/altitude axis ( Utilities/ShowPosition/AX1 ) - whether tracking in RA or not, I have found this figure to be constant as soon as the mount has finished moving to the target.
- on hand controller display the Celestial declination ( Utilities/Show Position/DEC ) - it is this figure that is slowing increasing ( ~ 5" / min ) ( note it does not change if tracking is set to "off" ).

Does anyone else have this "issue"?

Do you have any ideas what it could be?

 

Note that this has nothting to do with PHD or flex of the tube or imaging system - the above is just related to the declination information being displayed ( and exported ) by the Synscan unit.

 

Much appreciated, 

Mike

[ronin]

It may make sense, especially as you are talking of ~ 5" / min. I only say "may".

When you set the mount up and performed the alignment tne the mount has determined the errors that it needs to compenstae for, one of those will be the declination angle changes that it needs to apply. So slowly the Dec angle is altered at the scope.

My guess is that the mount is in effect displaying these small compenstaations (for some reason). The data for this will be coming from the movements that the Dec motors are required to make in order to maintain the target in the center of view.

It might make more sense to not display them and it makes a question of if the target remains centrally in view then what are the coordinates that the scope is using for its position, and how does this effect subsequent movement.

It would make more sense to get the target in view and central then simply hide the compensation movements from the user, but something may have chamged or someone thought it a good idea or the code is a bit in error and displaying the movement.

All this depends on the target remaining central in the view.

[dph1nm]

Skywatcher mounts do not drive the dec axis at all - so the true dec the scope is pointing at will drift depending on the accuracy of the PA (this is how drift alignment works). In principle the mount knows the size of this error from the alignment stars, so I guess it could be showing what it thinks the true dec is. I must admit I hadn't noticed this and I didn't realise the handset was quite that sophisticated - but maybe it is!

NigelM

[dph1nm]

Question - what happens if you set it to track without performing an alignment (I guess you might need to clear any existing data)?

NIgelM

[Merlin66]

The RA axis is then driven at the selected rate - sidereal solar lunar etc.

I use this "method" all the time for solar observing.

 

[MikeODay]

21 hours ago, ronin said:

It may make sense, especially as you are talking of ~ 5" / min. I only say "may".

When you set the mount up and performed the alignment tne the mount has determined the errors that it needs to compenstae for, one of those will be the declination angle changes that it needs to apply. So slowly the Dec angle is altered at the scope.

My guess is that the mount is in effect displaying these small compenstaations (for some reason). The data for this will be coming from the movements that the Dec motors are required to make in order to maintain the target in the center of view.

It might make more sense to not display them and it makes a question of if the target remains centrally in view then what are the coordinates that the scope is using for its position, and how does this effect subsequent movement.

It would make more sense to get the target in view and central then simply hide the compensation movements from the user, but something may have chamged or someone thought it a good idea or the code is a bit in error and displaying the movement.

All this depends on the target remaining central in the view.

 

Thanks Ronin

I don't think that the dec motor is moving - the Synscan reports that the declination/altitude axis is not changing ( Utilities/show posiiton/AX1 ).

The problem I have is that, despite the axis not moving, the Synscan reports that the celestial declination is continually changing, and at a rate that would appear to be too high to be just due to the polar alignment error saved by the Synscan after 3 star alignment.

[MikeODay]

14 hours ago, dph1nm said:

Skywatcher mounts do not drive the dec axis at all - so the true dec the scope is pointing at will drift depending on the accuracy of the PA (this is how drift alignment works). In principle the mount knows the size of this error from the alignment stars, so I guess it could be showing what it thinks the true dec is. I must admit I hadn't noticed this and I didn't realise the handset was quite that sophisticated - but maybe it is!

NigelM

Thanks Nigel.

Yes I thought that might be what it is trying to do.  However, at one stage during my testing, the polar alignment error was less than 15" in either axis and accoding to an online calculator 

( http://celestialwonders.com/tools/driftRateCalc.html ) this should result in a drift rate << 1" /min rather than the 5"/min drift according to the Synscan

13 hours ago, dph1nm said:

Question - what happens if you set it to track without performing an alignment (I guess you might need to clear any existing data)?

NIgelM

I have not tried that - I'll have a go next time.

Do you have a Synscan 4, have you noticed this - I'm am trying to figure out if my unit has a problem or if it is a "feature" of the firmware.

[MikeODay]

13 hours ago, Merlin66 said:

The RA axis is then driven at the selected rate - sidereal solar lunar etc.

I use this "method" all the time for solar observing.

 

Thanks Merlin.

[MikeODay]

I ran a few additional tests last night ...

When tracking with PHD2 in RA and DEC, the declination angle reported by the Synscan still continues to change but at a slower rate.

And,

Without tracking with PHD2 and just the normal sideral RA tracking by the Synscan, the direction and rate of dirft is the same regardless of which side of zenith I set the altitude of the scope.

 

[dph1nm]

On 05/08/2017 at 04:10, mike005 said:

Do you have a Synscan 4, have you noticed this - I'm am trying to figure out if my unit has a problem or if it is a "feature" of the firmware.

Yes, but unfortunately the obs is out of action at the moment (needs a new roof!). I don't remember anything like this from last season, but I suspect I may never have looked. I have been more concerned trying to get the EQ8 to track in RA ...

NIgelM

[MikeODay]

On 07/08/2017 at 23:40, dph1nm said:

Yes, but unfortunately the obs is out of action at the moment (needs a new roof!). I don't remember anything like this from last season, but I suspect I may never have looked. I have been more concerned trying to get the EQ8 to track in RA ...

NIgelM

Sorry to hear about your observatory and your problems with tracking.  I should count my blessings   - PHD2 tracking ( in RA and DEC ) seems to be working ok for for me ( even if the Synscan incorrectly says that the DEC is changing )