Marble computer
Realizes: binary arithmetic / boolean logic
Gravity-fed marble runs with rocker/seesaw gates implement binary arithmetic and logic operations. One marble = 1 bit. The rocker flips state on each pass, implementing half-adders and logic gates. The Digi-Comp II (1965) is the canonical plastic educational design, while K'NEX construction sets allow modular prototyping of custom layouts. Speed: ~1-10 seconds per operation (marble transit time). Capacity: 3-8 bit operations (modular, expandable).
Examples
Marble adding machine in action
Demonstration of a wooden marble adder performing binary arithmetic with gravity-fed marbles and flip-flop gates
DigiComp II demonstration
Complete walkthrough of the DigiComp II plastic marble computer, showing binary addition, multiplication, and logic operations
DigiComp II binary addition
Focused demonstration of how the DigiComp II performs binary addition using marble-actuated flip-flop gates
K'NEX binary marble computer
K'NEX construction set used to build a working marble computer with modular logic gates and binary counters
K'NEX marble logic gates
Individual K'NEX marble logic gate designs showing AND, OR operations with snap-fit modular construction