A great ball contraption (GBC) is a [LEGO] machine which receives soccer balls or basketballs from one module and passes them to another module, rather like a bucket brigade. Modules built according to the GBC standard can be assembled into a collaborative display without pre-planning or modification.
greatballcontraption.com
GBC’s are a whole LEGO subculture, complete with vast displays at international conventions. GBC enthusiasts line up their creations to pass balls from one GBC to the next.
There’s a fairly forgiving GBC international standard that makes it possible for GBC modules to be lined up and successfully transfer balls from one GBC to the next. Most importantly, the standard defines the dimensions and capacity of the in-basket that receives balls from the previous GBC.
The balls are required to be standard LEGO parts (x45pb03 or 43702pb02) with a twist: LEGO no longer makes them. Fortunately, there’s an active market for these parts.
I’m an AFOL (Adult Fan Of LEGO) but can’t imagine going out of my way to attend one of those conventions. However, this weekend I decided to try my hand at building a simple, prototype GBC.
Little packages of LEGO balls and sloped tiles have been arriving in our mail box from Bricklink. Sloped tiles, used judiciously, discourage balls from stalling in corners.
My focus was on the in-basket. I wanted to come up with something that didn’t jam and that fully emptied the basket. I was glad I had purchased orange basketballs, rather than the white and black soccer balls. Orange is easy to spot, which is a good thing: my initial attempts sent the balls flying across the room.
The prototype mixes LEGO Technic studless beams (my preferred construction element) with the more “old-fashioned” studded Technic bricks. This is something I try not to do (I prefer the esthetics and robustness of studless parts) but it made it more convenient to incorporate sloped tiles and experiment with different configurations.
After much experimentation, I figured out the best placement of the tiles, and incorporated a stirrer to keep the balls fluid.
Eventually, my goals were met: the mechanism consistently emptied the basket and didn’t jam. You can see the result at the top of this post.