GraviTrax compatible tracks

With [more piers](https://www.thingiverse.com/thing:2738439) (or posts, pillars or how you call them) you will need more tracks for bridges immediately.

I made some for my sons.

There is also an extra long track rail that is not available in the original GraviTrax set that covers 4 bases (!)

Links to my other GraviTrax compatible parts:
Curves, Straights, and Joins: https://www.thingiverse.com/thing:2738494
Pendulum ball starter: https://www.thingiverse.com/thing:2738573
Magnetic cannon: https://www.thingiverse.com/thing:2738601
Bridge piers: https://www.thingiverse.com/thing:2738439