Among the many amazing, fantastical things common to LEGO conventions, the Great Ball Contraption is a standout. It is essentially a Rube-Goldberg-esque machine that exists solely to justify its own existence. We’ve written about the Great Ball Contraption (GBC) a few times here, and most recently Ronald wrote a great walkthrough of how to get started building your own module.

Ever since my first LEGO convention, I knew I wanted to build a GBC module. When our kids were old enough to attend a convention, they were similarly bitten by the GBC bug. Last year, for Christmas, I told my son that if he worked with me to build a GBC module, I’d pay for the parts to build it and a trip up to Seattle so we could enter it into BrickCon’s 2024 Great Ball Contraption. He was on board so we got to work.

Design or Borrow a GBC?

First, we had to decide if we were going to design our own module or use someone else’s design. For a few weeks, we tried to build different prototypes to see what would spark our interest. We got some interesting movements and some lightbulb moments, but ultimately, we couldn’t string a full module together.

We took a look at Planet GBC, a great resource to get inspiration for a GBC module, purchase instructions, or even purchase an off-the-shelf kit. At first, we picked out a module that would have been about $100 after shipping. I consulted with a colleague who’s done modules before, and he strongly advised that we start smaller, simpler, and then source bricks from BrickLink instead. We took this idea and it really paid off. (A quick fast forward: after one weekend running the module we learned that anything that can break will break. It’s almost comical where those little balls end up.)

To find a module with instructions, we searched Rebrickable for “GBC Module” and after looking at a few options chose the CradleTipper by Stork:

If you’re considering entering a GBC, I can’t recommend more to start with a simple model. It makes soaking up the experience and taking notes for next time a lot easier. This particular module played well off of the parts we had on hand and seemed simple enough in terms of the number of mechanisms at work. Here’s the module at work:

We scoured our collection for parts, and after a BrickLink order and a few substitutions, here’s our first GBC module:

The first thing we did after completing the model was testing, obviously, but then we let it run for a few hours just to make sure we found any issues or loose connections. We were really happy with what we made, the model we chose, and how it all came together. It was also fun to go through this whole process with my son. Seeing his face light up the first time the balls did what they were (mostly) supposed to do was such a blast.

Meeting the Team

This being our first MOC on display ever, I won’t pretend to be an expert, but this was our experience. It’s common for a convention to run from Thursday to Sunday, with the public only being allowed in on Saturday/Sunday and the other days for builders. I could only rationalize taking our son out of school for one day, so we drove up Friday morning.

Walking into the exhibit hall, everything still felt very much in ‘setup’ mode, so we didn’t feel like we’d missed anything. Walking up to the GBC section, we introduced ourselves to the team and ran into our first problem. “Is that your only power source?” said one builder, forlornly looking at our sad little battery box. For a moment, I thought we had made a big mistake but then fellow builder and PORTLug-er Rick Vogt came over and saved the day. Rick is a GBC veteran with a number of cool GBC modules. He said we could plug our motor into one of his 9V speed regulators and gave us the lay of the land.

These 9V speed regulators are a must if you want to participate. Beyond long-term, consistent power, you can also save yourself from messing with gear ratios by turning the power down to slow a motor. We were shown our spot, put our name tag down in front of the build, and slotted it into the GBC track. And just like that, we had achieved a long term LEGO goal!

The other modules on the track ranged from similar sized/sope to ours to a Tron module that was taller than me by Diego Barca. (Extra points for the Ninjago t-shirt from our baseball excursion!)

In the early evening of Friday, we did a walkthrough of the whole track. This allows builders to explain common fail points, fixes, or quirks so that anyone on the team can fix a module if there’s an issue. In addition, we learned that they keep a small number of modules on hand to swap out if someone needs to tinker with their module. One of my favorite memories of the trip was a group of grown adults listening intently as my 8-year-old son explained our GBC module. Everyone took him seriously, and he felt so chuffed to be included.

In the Pit for Public Hours

We got to the hall on Saturday an hour before the doors opened to the public. I thought we’d feel nervous, but Rick and the team made us feel prepared. At 9 am, the doors opened and we were almost instantly swarmed. My son stood behind his module and answered questions as they came in. Everyone kept asking him how he got to be on the other side of the table, and he would proudly point to our module and say, “I built that!” Here’s a view from behind the rope:

GBC builders should expect to spend most of the weekend behind their modules, both to watch your module but to be also to be a part of the team. That said, with an 8-year-old’s attention span, Rick graciously offered to watch our model so we could take breaks here and there. When we returned, we learned that our model didn’t have a single issue the whole time. We chalk this up to its simplicity, as well as its speed. It turned out we were also the slowest module in the track, which can be a good thing. Having slow modules here and there keeps the balls from backing up in the track—it works to regulate the whole track.

Here is a video from Beyond The Brick showing the full track. You can see our module at the 6:40 mark:

Overall, this was a wonderful experience,, and we couldn’t recommend getting involved more in GBC—especially if you’ve been on the fence. The friends we made that weekend really helped get us up to speed. We’re planning on bringing this module, and hopefully some new ones, to both Bricks Cascade and BrickCon this year. Say hi if you see us!

Do you have any stories about getting started with GBC? Let us know in the comments below.

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