There’s a peculiar subset of Lego fan that doesn’t spend their time building perfect replicas of iconic cars or elaborate brick-built model railroads. They instead create Great Ball Contraptions, or GBCs, for short: complicated contraptions that do nothing more than move tiny balls from area to another.
It sounds like a pointless hobby akin to creating Rube Goldberg machines, but in reality, the thousands of Great Ball Contraptions builds you’ll find online demonstrate some of the most original and complicated Lego creations ever assembled. Each GBC is an expression of its builder’s unique skills and interests, and the only thing more fascinating than watching one in action is watching hundreds of them lined up at a Lego convention creating a gigantic ball moving factory. Here’s some of our favourite GBCs, but be forewarned: It’s a deep rabbit hole you might not want to fall into.
Basketball Player Roulette GBC Module
NDL-GBC has shared a small collection of their GBCs on YouTube, but their most creative takes advantage of the short-lived Lego NBA sets. Those included not only the tiny basketballs that many GBCs use, but also minifigures with spring-loaded legs that could actually shoot free-throws. In this GBC, a never-ending circle of pointy-headed Lego NBA minifigures grab a basketball from an animated stair lift and then shoot it into a net with perfect accuracy.
You can find the instructions to build this one yourself on Rebrickable, but you’ll first need to stock up on those spring-loaded minifigs.
Robot Dreams GBC Module
If you’re passionate about Lego, you need to start following JK Brickworks on YouTube. It’s where Jason Allemann and their partner Kristal share their incredibly polished Lego creations (two of their custom builds have actually been turned into official Lego sets), including this GBC that features a production line of robots picking and placing balls that are passed along to each other in the process. It demonstrates not only Allemann’s artistic skills, but their mastery of Lego Technic that brings the collection of bots to life.
Five Tilted Rings GBC Module
Some of the best Lego GBCs leave you wondering if the laws of physics are being bent or broken, and that’s the case with Akiyuki Brick Channel’s contraption. It features five spinning off-axis rings that somehow manage to pick up balls and pass them between each other, eventually elevating them to a drop-off point. The complex Technic gearing alone in this build is a masterpiece of engineering, and we could watch it in action for hours on end. Full instructions to build your own are shared here.
Pneumatic Ball Factory V2.0
Three electric motors, 17 pneumatic pistons, three servos, and almost 60 inches of Lego conveyor belts power this GBC by Quanix, which looks like a miniaturized version of a car factory. Robotic arms pick up individual balls and load them onto palettes which are shunted around the tiny factory on conveyor belts. It’s a joy to watch in motion, but with more than 3,000 parts it also looks like it was a nightmare to build, especially when it came to routing and organising all of the pneumatic tubing so it wasn’t in the way.
Akiyuki Marble Run GBC Module
It might look like a roller coaster where balls are lifted to the top of the structure so that gravity can bring them shooting down the rails to the bottom, but Berthil van Beek’s marble-run GBC actually works in reverse. A pair of giant Lego flywheels spinning at over 1,000 RPM propel the small balls up the inclined tracks until they crest at the top and gravity takes over, bringing them back down to ground level.
Lego Railway System GBC Module
One of the largest single GBC creations we’ve ever seen, Akiyuki Brick Channel brings Lego’s wonderful train sets into the mix. This contraption features an entire miniature railroad with self-powered cars that load up on balls and eventually deliver them to a tipper that rotates each one upside down to empty it out. The video is worth watching, not only to see the layout in action, but also the clever engineering that controls the timing of the rail cars to ensure there’s never a catastrophic collision. You can find the instructions to build your own here.
Lego GBC Jurassic Park
Who doesn’t love a good story about science and technology running amok? It’s why Jurassic Park was such a huge hit, and is somehow even better when turned into a GBC. In Josh DaVid’s recreation of the scene where the T.rex escapes its paddock, the dino doesn’t dine on goats and lawyers but balls instead. Every time it leans forward, it grabs another ball and then leans back to swallow its meal, at which point the balls are dumped out onto another track to complete their journey. Life finds a way.
Strain Wave Gearing GBC Module
As unorthodox designs go, it doesn’t get much stranger than Akiyuki Brick Channel’s GBC built around a strain wave gearing system where an elliptical inner gear rotates inside a larger circular gear. To make the different shaped gears function together required some incredible Lego Technic engineering, and watching what’s going on behind this GBC is just as fascinating as seeing it pick up and drop balls as it makes its rotations. You can see a breakdown of how it was built here, but do your brain a favour and don’t try to build your own.
Lego GBC EV3 Writer
Going above and beyond the call of duty, the YouTube channel 20100 shared this GBC EV3 Writer, which doesn’t just move balls from one container to the next, it sorts them by colour — white and orange — and then releases and arranges them to spell out custom messages on a display tray. It’s even slower than an old ‘80s dot-matrix printer, but somehow that makes watching it in action even more captivating.
Great Ball Contraption Tower
There’s so much happening in this Great Ball Contraption Tower designed to look like a skyscraper under construction that you’ll probably want to watch through this video again and again just to take it all in. Diego Baca stacks several different approaches to GBC construction into one machine that’s so elaborate it’s powered by an app running on Windows 10.
Invisible Lift GBC Module
The video’s 7 years old at this point, but Akiyuki Brick Channel’s Invisible Lift GBC Module still deserves recognition for its incredibly clever use of clear Lego pieces to create a ball lift that appears almost invisible from the right angle. It’s not just a neat effect, as you can see from the complex structures on either side of the lift. Using small Lego poles to securely grasp and raise a ball isn’t easy, and a mountain of Technic engineering had to be thrown at the problem to get the lift to function properly and reliably.
Catch and Spin Robots GBC Module
The best GBC modules are also the most deceptively simple ones. Here a pair of red and yellow robots patiently wait for a ball to be delivered while eagerly clapping their hands and bobbing their heads like a pair of synchronised swimmers. Those rhythmic motions continue until the robots finally grasp a ball, at which point an elaborate Technic mechanism is activated causing the robots to spin 360 degrees while delivering the ball onto a higher platform. A hidden network of complex gearing powers the highly choreographed routine, and it reinforces the fact that the Akiyuki Brick Channel YouTube channel is responsible for some of the best GBC creations out there.