Lego Great Ball Contraption (GBC) Balls

thingiverse

GBC is the term for a series of LEGO modules passing Lego soccerballs and basketballs from one module to the next. I have recently built a few custom GBC modules, but found myself at a loss as to acquiring the balls. The only place to get them is from LEGO or Bricklink, and factoring in shipping they cost approximately $1.50 CAD per ball. Ouch. Instead of paying that exorbitant price, I made my own. The design was easy - I spent only 5 minutes in Tinkercad - but the printing was tougher. In order to work with catapult modules, the balls have to have a very similar weight to the originals. Here's a list of what I did to make them weigh and print correctly. #Run a flow test. Make sure you do this. I won't go into detail here as it's explained in many other places online, but without this the halves and peg will not fit together. #Adjust your infill. Turn off all helpers (supports, brim, etc.) in your slicer and load two halves and a peg. Then slice and check the estimated weight. The trick is to keep re-slicing until your weight is around 1.52 grams, give or take .05 grams. Then add your helpers in again and re-slice. This should give you a pretty close weight, though it may not be precise. I take the result, weigh it on a gram scale, and adjust my infill accordingly. Repeat printing, weighing and adjusting until your weight is accurate. Note that you generally don't need to do this for most modules to work, but I like for my balls to be as close as possible. #Print at high resolution. Make sure you print at around 0.05mm layer height so the balls will roll. If you reduce the resolution much more than this, the balls will jam up some modules. I think that about covers it.