Image of the day

Captured by
Preston Luckey


My Account

New to Astromart?

Register an account...

Need Help?

Virtual counterweight for AZ3 mounts

Posted by Malcolm Bird   03/05/2016 12:00AM

Virtual counterweight for AZ3 mounts
Virtual counterweight for AZ3 mounts

The Vixen AZ mounts, Celestron brand labeled versions, and the Chinese knockoff AZ3 mounts are out there by the thousands and they all have the same problem.

They are so out of balance when moved towards the vertical, that the Altitude axis nut has to be tightened to the point that moving the telescope in altitude is very difficult. It is hard on the telescope OTA if you are using it for leverage and slackening the nut to get easier motion just results in Altitude creep. There is no lock on the Alt axis to address this. The nut is the lock and it is a very fine line between being tight enough to prevent unwanted movement and so tight that movement is difficult.

I experimented with a variety of traditional counterweight solutions but none were easy to implement and required modifications to the mount.

What I finally came up with was a simple tension spring that is connected from the top of the scope mount plate to the base of the mount. In the horizontal position where the scope is in balance, the spring is relaxed. As the scope moves further away from the horizontal towards the vertical, the spring tension increases to compensate for the out of balance. A virtual counterweight.

The picture is of a Vixen-Celestron AZ3 and there was a handy point to mount each end of the spring. I cannot recall if the Chinese AZ3 mounts had these same bits to attach to.

With the spring in place, you can slack off the altitude locknut to get much easier motion. Just leave it snug enough to create a bit of drag and act as a clutch. The spring can be attached without modifying the mount, and it does not affect the slo-motion controls.

The relaxed length of the spring is 5in and it has about 8lbs of tension. The spring that is right for you will depend on the size/weight of scope you are trying to counterbalance. The mount in the picture has an 80mmF11 refactor on it.

The spring is not critical, but do not use too strong a spring as you would then have to tighten the nut to prevent unwanted movement in the opposite direction. A slightly weaker spring would simply require the nut be a little snugger to compensate. I had a variety of springs laying around my shop and I just tried a couple till I reached a happy compromise. I also drilled and tapped the mian nut for a set screw, instead of retaining the jam nut approach to locking the nut.

This simple trick makes the AZ3 a much easier and pleasurable mount to use.