V2 Gravitrax Thingitube

The design of the flipping part is altered and should now print without problems on most printers. Added a STL file - supplied by Marcel_X - that replaces the need for a special metal axle.

A sincere Thank You to Marcel_X and basti_vapes for their comments and input which made the improvments possible.

Please note that the balance of the flipping part depends on how solid it is printed. On my Flashforge Finder with print setting "fine" it comes out well balanced. "Fine" stands for 3 perime