Tuesday, 19 June 2018

Adjusting the azimuth clutch on a Skywatcher Star Discovery mount.

Unlike the Synscan AZ, GOTO mounts, the Star Discovery Mount has FreedomFind™ dual encoder technology. This allows the mount to be pushed manually in either axis during use, and the controller keeps track of where the mount is pointing. The altitude axis has a sturdy clutch release and adjuster. However, the azimuth axis does not. With use, it is commonly found that the azimuth clutch becomes slack and the mount can be turned manually too easily. Even a gust of wind might be able to turn the scope on the azimuth axis.

Four screws hold the plastic top on the mount. When this is removed the double clutch assembly is exposed. The bottom clutch controls how difficult it is to manually turn the azimuth axis.

A spanner was made by hammering and filing a tool that came with a self assembly item, until it was wide enough to slide onto the flats on the bottom clutch. There are two Allen-key grub-screws between the flats opposite each other and these are slackened off with an Allen key. The clutch is then turned a very tiny amount clockwise and the grub screws tightened.
It is clearly a matter of trial and error to get the adjustment right, but this procedure works. It is best to turn the clutch by an almost imperceptible amount at one go. If it is overtightened, then the mount will stall while slewing in certain directions due to some asymmetry within the system.

Manufactured spanner and Allen-Key

The spanner engaging the flats

One of the retaining grub-screws is visible
I don’t know whether this procedure will invalidate the warranty, but I found that without doing it, the mount was virtually unusable. Nowhere in the manual is it explained how to correct this problem.

I use this mount as a substantial, quick setup, AZ GOTO mount for Solar system and deep sky observing and imaging. Previous postings on this blog show the mount in action. Of course there is image rotation, but as long as there is no perceptible rotation within images, then Deep Sky Stacker and lxnstack for example, are able to de-rotate the images during stacking. Keeping the azimuth clutch adjusted correctly is going to be critical for the continued use of this mount.