Building the World's First Computer: Babbage's Analytical Engine

 I finally got my prototype to do a real calculation: computing the Fibonacci sequence F(n) = F(n-1) + F(n-2). Started with 1 and 1, the sequence is 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377,... Here's a still image after it just computed 233, and here's a video of it computing all the numbers from 2 to 377 in less than two minutes. (The resolution is poor because Blogger has a 100MB limit on videos; see https://youtu.be/I2eggg87dSU for a better version on YouTube.) It's running at the full "Babbage speed" of 157 milliseconds per digit. I consider this my first real milestone! There are three phases to the computation, assuming F(n) is on digit wheel A1, F(n-1) is on anticipating carriage wheel F, and digit wheel A2 is zero. add A1 to F, while simultaneously preserving A1 by copying it to A2. move F to A1 move A2 to F Repeating that generates the Fibonacci sequence on A1. Below is the detailed microcode.  Each quoted string lists the operations that are exe...

Part of the motivation for using 3D printed parts to to explore the limits of what can be done to implement Babbage-like mechanisms with parts that have poor dimensional accuracy. My Lulzbot Taz 6 printer has a nozzle diameter of 0.5mm, which is 0.02", or 20 mils. The feature accuracy is probably twice that, or 40 mils. Standard machinist tolerance for metal fabrication is 5 mils, so we're about 8 times worse. There are many places where the inaccuracy doesn't matter, or where a little hand-finishing with sandpaper can improve the fitness. But there are some cases, especially where two printed parts interact with each other, that are unfixable. One example was the scheme I had devised for digit wheels that allows them to stack without resting on each other even though there are no framing plates like Babbage used for many of his designs. When built entirely with 3D-printed parts, it required two concentric cylinders to fit closely together. It's a bit of a challenge to...