According to Brian Davis' lexicon, a great ball contraption step feeder has a series of vertically oscillating ledges or steps, each just a little bit higher than the preceding step. The first step lifts a ball out of the bin, and at the top of the lift the ball rolls onto a static step with another moving feeder step on the other side, which repeats the process. Steps can be driven by cams on a central drive shaft at the base (or partway up). Steps in fact can be any width or length down to the nominal size of a single ball. The mechanism can be seen in this animation:
- Single-acting: odd-numbered steps oscillate up and down synchronously, while even-numbered steps are stationary (passive "holding pens"). Since all the moving steps are synchronous, they can all be part of one structure, moved by a cam at the base. It is also possible, if the step is the width of a ball, for half the step to oscillate and the other half to be static.
- Double-acting: every step moves up & down, with alternate steps 180 degrees out of phase, potentially much faster.
- Using rotation instead of linear vertical motion. See Cloud example below.
It is also possible to combine elements of these different types into one module. For instance, as shown in the animation above, every second step is static (like for single-acting), and each moving step is 180 degrees out of phase (like for double-acting).
|MOC||builder||explanation given||image available||video available||instructions available||follows GBC standard|
|Cloud||Torso||brief||123||YouTube||no||Front and back of in-basket are too high|
|Module name||Builder||Has instructions|
|LEGO GBC Stair Lift||Josh DaVid||Alas no|
- "The Great Ball Contraption." <http://www.teamhassenplug.org/GBC/contraptionideas.htm>.