Lego GBC Balls

GBC Balls are a quintessential part of Lego Great Ball Contraption, without them it would just be a bunch of strange contraptions.

The typical ball is a Lego sports ball most often recognized in their soccer and basketball printings, however, these balls have not been produced for many years and although plain orange and white counterparts are still produced they can be expensive to procure in large quantities.

So I set out to do a comparison of Lego vs some non-Lego balls as well as compare the UV properties.

Properties of the Lego sports ball

Lego sports balls have two key properties that impact GBC modules design,
these being

  • Diameter: 14.00 mm
  • Weight: 1.50 grams (~0.05oz)

Depending on your module style will depend on how much these can be varied when using non-Lego balls.

Module styles that are tolerant of ball changes

Typically Chain, Stepper and Saw-Tooth based modules will tolerate a wide range of ball weight and size changes as their operation does not depend directly on the properties of the ball

Module styles that are NOT tolerant of ball changes

Modules that are designed based on ball geometry and weight can have varying levels trouble with non-Lego balls.

These modules are

GBC Module Style Weight matters Size matters
Picking / Grabbing Possibly Yes
Shooters Yes Yes
Ball pumps No Yes
Weight Tippers Yes Possibly


For my comparison I wanted to test size and weight and also the UV properties of some of the non-Lego balls

  • 14mm UV  Beads
  • Lego Sports balls
  • PV-Productions UV balls
  • 14mm plastic beads
  • Lego UV parts (a spider and a ghost)


Size and Weight Results

For weight I used gram scales and took the average of several measurements for each item.

Dimensions was the same process, although this was a little harder as none of the test balls was perfectly round.

TestItem Weight Weight % of Lego Diameter Diameter % of Lego $/100
UV Bead 1 1.38 92% 13.9 99% $6
UV Bead 2 1.41 94% 13.8 98% $6
LEGO Basketball 1.49 99% 14.08 100% $40-$120
LEGO Soccer Ball 1.51 101% 14.08 100% $40-$120
PV-Productions UV 1 1.67 111% 13.9 99% $60
PV-Productions UV 2 1.64 109% 13.85 98% $60
Bead – blue 1.31 87% 13.6 97% $20
Bead – green 1.42 95% 13.6 97% $20
Lego UV – Spider 0.36 24% 20 142% $48
Lego UV – ghost 3.02 201% 40 284% $150

UV Results

For UV testing I did three separate tests where I changed the amount of time the items were under UV light, these were for

  • 1 second
  • 5 seconds
  • 10 seconds

However when I compiled my discharge results there was no consequential difference between a 1 second or a 10 second soak, which means when “charging” balls for night time running soaking a ball for long periods is not required.

Test Item Time to discharge (seconds)
PV-Productions UV Balls 120
Lego UV 60
UV beads 5

Final Thoughts

If your are designing Chain or Stepper based modules, all of the balls here would work fine (the spider may not roll very well)

For Shooter and Picker modules even a 0.1mm change in diameter or a 0.1 Gram (or 0.003oz) difference can change the behavior of the module and I would strongly recommend acquiring genuine Lego sports balls for testing and tuning these kind of modules.

For glowing UV balls PV-Productions are excellent outlasting Lego’s on UV materials by a factor of 2 and Lego aren’t producing UV soccer balls anytime soon, make a worthwhile investment.