A simple to make pan or cone that acts as a smaller portion of a ballscope, enabling 3 axis motion and sidereal tracking with a constant speed motor. This design works because the eyepiece is best positioned to the side and aimed upward.
Besides this webpage, check out my presentation at the Altaz 2024 conference. I describe the pan / cone mount at the end of my one hour talk.
Inspiration comes from removing sections of a ballscope like this.
I cut out a paper model to verify smooth motion and sidereal tracking. I then purchased an inexpensive squirrel baffle made from sheet metal at a hardware store.
How to cut the pan or cone is easily calculated.
The altitude brake is two Teflon pads pressed against each other. Wonderfully smooth and able to handle the unbalance caused by a heavy eyepiece and coma corrector.
Details of the two wood rings that I cut out and fiberglassed to the squirrel baffle. The pan / cone moves easily in a plastic bucket and demonstrates that it is essentially spherical.
The 45 degree pan / cone of the 6 inch is fine for that size, but in larger apertures becomes too big. The pan ideally needs to be closer to 30 degrees. This fits nicely under the 30 inch f2.7.
Driving the pan / cone is similar to driving a ballscope, per Jerry Oltion and Pierre Lemay. I estimate a +-0.5% tracking error because of the flat pan instead of a rounded ball segment.
However, with the 30 inch pan / cone at a 30 degree slope and being at 45 degree latitude, this means that I have to adopt the thinking of equatorial table enthusiasts who use great circles about the latitude axis. These can be reversed and combined into a single pivot.
