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MikeODay

Help please: Synscan / EQ8 problem ( feature ?) - declination reported by Synscan keeps changing

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I am trying to understand why the declination position reported by my new EQ8 - Synscan 4 hand controller keeps changing.

After starting my aligned scope from Park the declination reported by the hand set ( Utilities/Show Position/  "Dec/Ra" ) slowly increases ( around 7" / minute when I first measured it ).  However, the  rotation angle of the declination/altitude axis of the mount ( Utilities/Show Position/ "Ax1/Ax2" ) is reported as being constant ( as one would expect if the mount is not receiving an instruction to move ).  That is, it would appear that the motor is not running and the encoders on the shaft are not detecting any rotation of the mount's altitude axis however the Sysnscan reports that the Celestial declination is slowly changing.

Does anyone know if this is a bug or a feature?

It did occur to me that maybe the Synscan is trying to compensate for the declination drift that would result from the Polar Alignment error as stored in the controller after alignment.  To test this, I adjusted the Polar Alignment to try to reduce the error and see if it changed the drift rate.  The initial results do not support this - after much tweaking of the alignment, and with an indicated polar alignment error of less than 15" in either axis, the rate of drift changed but was still around 5" / minute ( whereas it should be << 1 with so small a Polar Alignment error ).  

Has anyone else noticed this slow change in declination reported by the mount/Synscan when the mount is tracking in RA?

-----

EQ8 MC Firmware version: 2.11.04

Synscan HW version: 4.16

Synscan firmware version: 4.39.04

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Couple of simple things to check first :-

i) is DEC axis clamp fully tight?

ii) is scope balanced?

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3 hours ago, ngwillym said:

Couple of simple things to check first :-

i) is DEC axis clamp fully tight?

ii) is scope balanced?

Thank you for your reply.

Yes the Dec axis clamp is tight and the scope reasonably balanced.

I don't think that the declination axis of the mount is actually changing - in particular, the Sysnscan reports that the altitude/declination axis is not changing.  What is changing is the reported celestial declination.  That is, I think the Synscan unit is calculating the celestial coordinates of the point in space it is pointing at based on the readings from the encoders and the polar alignment and it is this calculated figure that keeps changing even though the scope is not actually rotating in the declination axis.  

I double checked last night.  If I turn of tracking on the Synscan, the reported celestial declination remains constant.

cheers

Mike

Edited by mike005

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10 hours ago, ngwillym said:

 

i) is DEC axis clamp fully tight?

 

I'll double check that the DEC clutch is not slipping.  My thought is that I will be able to do this by confirming whether or not the Synscan continues to report a change in declination while the mount is locked onto a star via PHD2 ( ie. tracking in RA and DEC ).

 

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