Adam Richard Cooper built this hand-cranked model of a classic mechanical governor–which, as MachinistBlog succinctly put it “regulates the speed of steam engines by acting as a negative feedback system”–and made the dimensional drawings and build notes freely available for download at his site. I like the idea of a hand-cranked governor model, particularly, because it provides tactile feedback of the device’s purpose: You crank it faster, it gets harder to crank.