Remembering an old toy from when I was a child, I found myself in the drawer of the glass marbles they were giving away in the Lidl discounters last year. They have a bigger diameter than the classic glass marbles, they are about 25mm. I have included a 26mm hollow sphere in the design. All it takes is 3 marbles to make this little UFO run across the floor.
I planned to print it divided into two parts because inserting spheres during printing would not have been possible. Just print the two parts, insert the marbles and glue them together.
I will probably print it in two different colors.

I'm going to print it tonight and will be posting photos soon.