What’s a LEGO GBC?

In the video playlist below you can see all of our LEGO GBCs created entirely from official LEGO sets. We made it really easy to get yourself started today!


Of all the things made with LEGO, our favorites are inevitably the Great Ball Contraptions. GBCs, as they are known for short, are a kind of Rube Goldberg-style machines designed with the sole purpose of moving tiny LEGO balls through a circuit. The GBC should not be confused with a Rube Goldberg machine, though. This device is not accomplishing a particular task, it’s just keeping the balls rolling.


A LEGO GBC is an elegant ballet of moving balls and each module of the machine has been carefully designed to efficiently move the balls individually or in groups on to the next component. The mechanisms that move the balls through the loop are generally as complex as possible, using clever actions that are reminiscent of the workings of a factory right out of How It’s Made. At the end it all starts over again.


We think, the Great Ball Contraption is just about the greatest feat of LEGO engineering that there is. The combination of planning, ingenuity, and commitment makes it challenging to put together a truly Great Ball Contraption. An extra challenge we take is the creating of a GBC entirely build from an existing LEGO Set.


We made it really easy to get yourself started today!

Check our LEGO GBC C Model building instructions


Design standards

When building a module you have to keep into account a couple of design standards like the dimensions, the location of a few elements and the throughput speed. In this way you can connect multiple module to each other.

With these as a basis, anyone interested in a big GBC loop can participate with a module. You can make it as simple or complicated as you like. As mentioned above, the objective of a GBC is to pass LEGO balls from one module to the next. Modules must conform to the following rules:

  • Each module should have an “In” basket, and will move balls to the next module’s “In” basket, which must be directly in line.GBC_02
  • The In basket should be 10 studs by 10 studs (outside dimension) with an 8×8 opening, and should be 10 bricks (beams) tall.
  • The front of the basket should be 32 studs from the back of the module. This will allow all modules to be lined up against a wall. The back of the module CAN be closer to the basket, but not farther.
  • The In basket should be located on the left side of the module, and output should go to the right.
  • There are no size limits, beyond those listed
  • Each module should be able to accept balls at an average rate of 1 ball per second. Balls can be passed continuously, or in batches. A batch should not exceed 30 balls.


As can be seen in the images, each module has an In basket. The Out basket is the In basket of the next module. Each module consists of a system that carries the balls from one basket to the next. This system can be as simple or complex as each participant wants as long as it manages to deliver 60 balls every minute, one by one or in batches no bigger than 30 balls. A basic module with the In basket on the corner can also serve to change the direction of the GBC 90º, allowing the modules to be placed in a closed loop. There is no limit to the length of the module as long as it complies with the rest of the rules.


Check our LEGO GBC shop to see all our models (created from official LEGO Sets) and start building yourself!


In the video playlist below you can see all of our LEGO GBCs created entirely from official LEGO sets.