12.5" Ballscope called "Ada"


Well, this past summer I finished my 12.5″ Ballscope. It took over 2 years to complete and I almost sold it a few times. I have already made some improvements and more are planned. Some of the improvements include:

  • Changing the base – Previously, I made a base with 6 teflon furniture pads angled at 45 degrees. When I tested the scope, it had noticeable backlash and wobble. I found out that the problem is that the polycarbonate ball itself is giving at the 6 points. I had two choices, reinforce the ball with fiberglass, or add more pads. I figured I should try to do the simple thing first so I changed to using regular teflon strips arranged around the 45 degree ring. This distributes the weight more evenly around the ball. The scope does not give now and the wobble/backlash has improved. I may go with a smaller tapered hole to further reduce the stiction. I am so used to using my Obsession (I recently sold this) that I like a smoother action. Will post my results later.
  • Reinforcing the top ring – The top ring is the ring that sits on the ball. There is a tapered ring inside of the ball that is slightly larger than the ball opening. The top ring and the tapered ring sandwich the ball opening between them. Right now, I use three bolts to compress the two rings together. I think this is not enough. I notice that at certain elevations (mostly when looking towards the horizon) there is more backlash than when it is pointing up. I suspect that the ring is giving at the truss sockets. So I will be adding additional bolts to compress those two rings together. Probably one on each side of the truss sockets.
  • Cooling – This scope does not have fans and right now I use a little camping fan sitting on top of the ball blowing cool air onto the mirror. I plan to either put a fan in the cover (like I did on my 8″ scope) or place some fans in the ball itself. Either way, I am attempting to avoid drilling any holes in the ball.
  • Dew Control – I hope to add dew control for the eyepiece and secondary mirror soon. The secondary poses a small challenge because it is simply the secondary glued to a 45 degree PVC dowel. I will probably use some hot glue and place some 1W resistors in series

I have had the chance to use it twice under dark skies and the scope is working well. I am very critical of the scope though because I keep seeing everything needs to be done to it. As I improve the scope, I am sure this feeling will diminish. Although I have been told that a scope is never truly completed.

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~ by jhissong on 2008/09/11.

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