Thie Great Ball Contraption, which I am calling my Rainbow Double Step, was designed by well-knowb GBC builder Maico Arts, for the 2017 Skaerbaek Fan Weekend GBC workshop. I didn’t attend, but the plans for this module are available on his website [as apdf download]. Once again, I easily found the pieces I needed to build the model. Its two steps are driven via a cam arragement which can best be seen from underneath. The steps are guided in their travel by two vertical shafts, and balls roll from the input bucket onto each step and are trapped by the 1×2 grille slopes until they hit the next step or the output wall.