Nexus DSC-mpoint

[dark star]

I have a 14 inch truss dobsonian which I made myself. I am trying to use Nexus DSC to locate objects, mainly galaxies and nebula. At the moment the best pointing accuracy I have got is within the general area, but a few telrad or eyepeice jumps away using my widest eyepeice. I assume this is because the mount is not square/orthoganal. Using the local sync function to sync on a star near where I am searching improves things but not enough to make it usable.

I am trying to build up a model of the mount in the DSC so it can correct for the mount not being orthoganal. This is called Mpoint. There is a problem with this. It will only let me add 4 calibrations points. I point at four stars in succession and press enter after beginning Mpoint start and the number increases up to 4. But then if I try to enter another star the number does not change. If I try to do Mpoint analysis it says that there are not enough calibration stars or I need to reduce the number of Mpoint parameters.I have the encoder instalation kit for skywatcher dobsonians.

I have now managed to increase the number of calibration stars to 6, but this is still not enough to get Mpoint working. Mostly, however many times I press OK when trying to add a calibration star the number does not increase, very occasionally it works.

The altitude encoder is a magnetic tape. I have entered the encoder steps for altitude as 1308000 according to the manaul for 12-14 inch skywatcher dobsonians. However, to fit the magnetic tape for the altitude encoder I used a small metal altitude bearing for a GSO dobsonian, which was spare from another project. I fitted this to the altitude bearing. This is according to the manual for GSO dobsonians.

I will try entering the encoder steps from the manual for GSO dobsonians for altitude which is 716000. Also, for some reason I entered the az encoder steps as 10000, I will change this to 8192. I will see if this improves things. When I fitted the metal altitude bearing I tried to get it centered on the axis of rotation as accurately as I could using  laser pointer.

Is anyone using nexus DSC with a dobsonian mount that is not very square? Does anyone know what the problem might be? Also, what parameters do I need for Mpoint for a dobsonian and which ones should I remove? There are a lot of parameters!

I have tested the encoders they work OK.

Over time I am going to try and test how out of square the dobsonian is and try and rebuild it to make it work better with the DSC.

 

David