A LEGO Difference Engine

Back in 1991, the Science Museum in London built a working example of Babbage’s Difference Engine #2. It took years of effort to produce that brass beauty.

Now Andrew Carol, a software designer at Apple, has designed and built several subsets of Difference Engine #1 out of LEGO components. Carol’s design is small and compact, and built using standard LEGO pieces.

“Babbage’s design could evaluate 7th order polynomials to 31 digits of accuracy. I set out to build a working Difference Engine using standard LEGO parts which could compute 2nd or 3rd order polynomials to 3 or 4 digits. I have built two generations of Difference Engines and am designing the third version now.”

Engine No. 2 relies on lots of vertical rods for translating information between the machine’s components. The plastic Legos were too soft for the task. But Babbage’s earlier design, No. 1, while more complex, works with gears, and Lego has gears aplenty. Once Carol had managed to get a key component working—a mechanical adder that retains the numbers being added—it took him three months to build his own, all-Lego, difference engine.

Lego Difference Engine 1