Great Ball Contraptions - GBCs for beginners - LEGO ball contraptions

A beginner’s guide to Great Ball Contraptions (GBC)

If you’ve been to LEGO shows around the country, you will no doubt have seen big loops of LEGO mechanisms pushing little plastic balls around.

These hypnotising mechanisms are known as Great Ball Contraptions – abbreviated to GBCs – and are created from many “modules” joined together, enabling huge “loops” to be created by many builders.

Where to find instructions and information on GBCs

GBC is quite an established format now, and there are some great resources online for both new and experienced GBC builders:

  • GBC standards – these are the standards to ensure that your GBC fits with other modules. The original standards are still online, but are a little harder to read
  • A good place to start for beginners is to build a well tried and tested GBC module –Brickworld workshop modules are a good place to start, as recommended by Huw who has given us plenty of tips for GBC beginners below

Tips for beginners to Great Ball Contraption

Here are some great tips for beginners to Great Ball Contraptions from Huw of Brickset.com, who’s a bit of a master when it comes to running GBCs at shows and exhibitions.

  1. Keep your machines simple and don’t be too ambitious: Akiyuki machines are fantastic and I’m sure his run perfectly, but they can be difficult to run reliably so are best avoided by the beginner hoping to run them all weekend. Brickworld workshop modules, are a good place to start.
  2. Don’t use too many balls: The GBC spec calls for machines to handle one ball per second, or a batch of 30 every half minute, but attempting to do so is asking for trouble. The BPM rate (balls per minute) will be largely dictated by the number of balls in the circuit so start off with a few then add more as the day goes on if everything is running reliably. On average, the circuits I’ve been involved with run at about 30 BPM.
  3. Have a couple of machines spread around the circuit that can act as ball reservoirs and flow regulators. Maico Arts’ stepper (PDF instructions here) is excellent for this purpose, especially if the input ramp is extended to 15 long.
  4. If you’re using Power Functions and powering from 9V train controllers, design your machines so that they operate normally when it’s at full power and turned clockwise. That makes it much easier for your collaborators should they need to address problems with your machines in your absence.
  5. Prioritise reliability above everything else: you do not want to be picking up balls and troubleshooting all weekend. Before the show, test, test, then test again!
  6. Build some ball boxes (8 bricks high, 8 wide studs width internally) that can be used to receive balls should machines need to be worked on out of the circuit
  7. Bring spare modules: keep them under the table just in case, especially if your modules have not been run at a show before.
  8. Bring a box of spare parts: gears can shatter, universal joints can break, machines might need modification or need to be connected together.
  9. Ball barriers at the front of tables [even just a brick built wall a few bricks high] are essential to stop strays from rolling off under the public’s feet.
  10. If the depth of the tabletops allows, fasten tablecloths to them using bulldog clips at the back and ends to prevent kids from tugging on them and moving the machines out of alignment.
  11. If you’re in a non-carpeted room, tables will get pushed by the crowd causing machines to be knocked out of alignment, so be prepared to keep moving them back.
  12. If you’re planning to use a ring of tables with an operating area inside, you will need at least one bridge, preferably two. One should be high enough to walk under.
  13. Also if planning to use a ring of tables, it’s handy to have one or more inside on which to work on machines.
  14. Take plenty of extension leads and use gaffer tape to tape them down in high traffic areas to save tripping over them.
  15. Finally, have fun and don’t get stressed out! Expect your modules to have issues: do not be disheartened, have replacements available and swap out as required.

What to take to shows with Great Ball Contraptions

Here’s a handy checklist of what to take to shows and exhibitions if you’re taking Great Ball Contraption modules:

  • Ball boxes (8 high, 8 wide internally) that can be used to receive balls should machines need to be taken out of the circuit for repair
  • Ball-poker, to poke balls out of hard-to-reach spaces. This could be just a long Technic axle.
  • Spare modules: keep them under the table just in case, especially if your modules have not been run at a show before
  • A box of spare parts: gears can shatter, universal joints can break, machines might need modification or need to be connected together
  • Ball barriers, for the front of tables to stop strays from rolling off under the public’s feet. They can be as simple as a 2 high wall built with 2×4 bricks
  • If you’re planning to use a ring of tables with an operating area inside, you will need at least one bridge module, preferably two. One should be high enough to walk under
  • Extension leads and gaffer tape to tape them down in high traffic areas to save tripping over them.
  • Large bulldog clips – these are really handy for keeping tablecloths out of the way
  • Tablecloths, if required by show organiser (Brick Alley members – we have tablecloths so you don’t need to bring any to our events!)

How to power your GBC loop

Many GBC builders use the 9V LEGO train regulator to power their GBC modules and these Power Function Extensions to connect from the regulator to the motor in your modules. You can stack multiple motors per regulator – typically 3 – 5 motors per regular is accepted practice.

Tips for running GBC at shows and exhibitions

  • If planning to use a ring of tables, it’s handy to have one or more inside on which to work on machines
  • Don’t use too many balls: the GBC spec calls for machines to handle one ball per second, or a batch of 30 every half minute, but attempting to do so is asking for trouble. The BPM rate (balls per minute) will be largely dictated by the number of balls in the circuit so start off with a few then add more as the day goes on if everything is running reliably. On average, the circuits I’ve been involved with run at about 30 BPM
  • Have a couple of machines spread around the circuit that can act as ball reservoirs and flow regulators. Maico Arts’ stepper (PDF instructions here), is excellent for this purpose, especially if the input ramp is extended to 15 long
  • If the depth of the tabletops allows, fasten tablecloths to them using bulldog clips at the back ends to prevent kids from tugging on them and moving the machines out of alignment
  • Watch for tables being pushed forwards by the crowds which can cause machines to go out of alignment. This is especially a problem in non-carpeted venue
  • Have fun and don’t get stressed out! Expect your modules to have issues: do not be disheartened, have replacements available and swap out as required.

That’s it – we hope you have fun with Great Ball Contraptions!