I built this platform in 1992, just a few months after getting the 20 inch Obsession. The main reason I bought a 20 inch scope rather than making one was that I didn't have the time to make something that big and time consuming. As I found out, building a platform is just about as time consuming as building a scope...
I bought the drive components from Tom Osypowski of Equatorial Platforms, and he generously supplied some photos and advice to help me along. As I've found out over the years, TomO is a true gentleman and I'm fortunate to count him as a friend.
The platform is a clone of his original cylindrical based design and is driven by a lead screw. This thing is robustly overbuilt and probably didn't even notice the 20 inch when it was sitting on it. It would track for 62 minutes and would turn itself off at the end of its tracking run. I'm still very proud of this platform.
This is a shot of the 20 inch Obsession sitting on the cylindrical platform. Who's the guy with the goofy smile and why is he wearing sunglasses in the shade?
The paper cone that helped me figure out the geometry of the conical platform design. The writing on the three photos explains what's going on...
Paper Cone photo 1
Paper Cone photo 3
This is the second platform I built for the 20 inch. Again following TomO's lead this platform is based on his conical design, which has the advantage of letting the forces of the scope travel more directly to the ground for added stability. Plus it weighed about 1/4 the cylindrical platform!
The conical platform geometry was a real head scratcher at first when I was trying to figure out how it worked so I could draw up plans. All became clear when I rolled a cone out of paper - see below - and traced a line around it. Pretty cool!
This platform was even steadier than the cylindrical version even though it was much smaller and lighter. One winter night I found out just how steady it was when I had my scope set up at Chuck Dethloff's place for a few very rare clear winter nights in the late 1990's. The ground thawed out during the day and re-froze each night, essentially cementing the platform's feet to the ground. While observing, the scope would barely quiver when I gave it sharp rap. Amazing.
I sold this platform when I sold the 20 inch scope in 2004 and I haven't seen it since.
This shows the 20 inch Obsession on the conical platform at the OSP in 2002 or 2003.
Paper Cone photo 2