The Great Ball Contraption Wiki


From The Great Ball Contraption Wiki

A great ball contraption conveyor mechanism moves balls up horizontally, vertically, or any angle in between.

These modules typically use a belt constructed of chain or tread links, with some raised parts (usually bricks or plates, or pairs of pins) that drag balls along when the belt is rotated.

Length of belt[edit]

Rafe Donahue has an equation for determining the number of links needed for a given conveyor belt length (using the Technic link with two pin holes). If one is using the small sprockets (part 57518) with six teeth, and these sprockets are spaced n studs apart, then the total number of tread pieces needed (t) can be computed to be t = 6 + (4/3)n.

Thus, if one is using a 13-stud-length beam and places the sprockets on axles at the ends of the beam, those sprockets will be 12 studs apart. Thus, to place treads around these sprockets, one would need 22 tread pieces because 6 + (4/3)*12 = 6 + 16 = 22.

Note that n must be a multiple of 3 for the total to be an integer.

This formula is not magic but is easily derived by noting that 6 tread pieces completely cover one sprocket. In a conveyor, one-half of each sprocket is covered on each end. That accounts for the "6" in the formula. Inspection reveals that 2 tread pieces span a distance of 3 stud units. Thus, along the top, and along the bottom, of the conveyor, each 3 unit distances requires 2 tread pieces. So, the total is made up of left sprocket plus right sprocket plus top plus bottom giving us t = 3 + 3 + (2/3)n + (2/3)n = 6 + (4/3)n.

If one uses the large sprockets (part number 57519) for a conveyor, then I would surmise (although I have not verified this experimentally) that the formula for the total only replaces the "6" with a "10" to yield t = 10 + (4/3)n. Proof of this conjecture is left as an exercise to the reader.  ;-)

The requirement for a whole number of links means that often the belt is slightly too long for the distance (and taking one link out makes it too short). In such cases, it may be necessary to use some sort of tensioning mechanism - something that changes the length of the path the belt takes - to take up the slack. This is most needed if the belt is being driven from the lower sprocket, but is not as important if being driven from the higher sprocket.


Ball throughput can be regulated by varying either the speed of the belt, or the density of the raised parts. For example, a belt as described above (constructed of links with pin holes wrapped around small sprockets) with pins in every sixth link being driven at 60 rpm will deliver (up to) 1 bps. One could achieve the same ball rate with pins in every third link, and driving at 30 rpm.


Brian Davis and SMART proposed several variations.[1]

  • chain-based: a continuous chain drive, with paddles or blades that sweep balls from the input hopper to the top. Benefits include that it could grab more than one ball at a time (depending on the conveyor width) and small footprint. A key design consideration is the input hopper geometry.
  • belt-based: a series of overlapping tank tread belts lift balls up shallow inclined path, with perhaps axles or other small thin parts keeping dumped balls from being pinched or spun between consecutive belts. It may be limited to very shallow slopes.
  • custom belt: a wide belt of frictionless-pin-linked studless beams carried and driven by various tires instead of gears. Might be heavy compared to a chain, but novel.
  • multi-bladed/propeller: a series of rotating blades project through the conveyor floor, such that the first rank of blades lift the balls up and forward, and as they rotate back down the second rank of rotating blades continues the process.
  • roofed: a smooth sloping floor of conveyor just holds balls against moving roof that pulls balls up the passive floor. Feeding may be a problem, and may be easier from the side rather than the bottom end.
    • tank-tread roof: balls roll up the floor ramp at half the speed of the belt, rolled by the moving roof above. May be limited to single tank tread length, as transitioning to a second belt is problematic.
    • custom or link-based roof: moving roof uses hanging paddles to snag balls in a pocket or cell, dragging them up the ramp.
  • The chain lift could be considered a variation.


MOC builder explanation given image available video available instructions available follows GBC standard
Ball Counter Module V1.5 LegoGBC yes no yes yes no
module de GBC 2 pg52, TeClem8 (Technic57) and Nicoboost no no YouTube no no
Module de GBB 2 pg52 no no YouTube no no
GBC Donahue Rafe Donahue, with Steve Hassenplug and Brian Alano PowerPoint (in English) yes Flickr multiple formats yes