Nested Spheres with Ball
by stevemedwin, published
The inner sphere spins freely on its axis while the ball bounces around (check out the movie in the downloads). The design started in GroBoto as four toruses for each sphere and then was twisted and assembled in Cheetah3D.
This model came out the best when I left some clearance between the points facing inward on the outer sphere and the cups on the inner sphere. Just be sure to clean out all the support structure that is needed for a successful build especially at the pivot points. The one pictured is about 42 mm in diameter and it took several hours to clean up so be patient! I printed an earlier version 63 mm in diameter before I added the points to allow the spinning.
I used ReplicatorG with 0.27 mm layers to print in white PLA on my Replicator2. The next time I print this it will either be with a thinner layer or larger scale.
The STL file is almost 200 mb so you might want to download the OBJ file and then convert it.