The Big Brother of our new GBC 18, Multiple GBC modules in one build, GBC 15 remains the biggest GBC we ever created! Tobias Witmer (NL) built it last weekend and, he too, got it running smooth as butter. Nice work! Up to your next Great Balls Contraption;) https://pv-productions.com/product/lego-gbc-15-42055-building-instructions/