In fact, if you watch the video in the article, it takes you through the 3 prior iterations. Hollow clock v3 had a gear that drove the hour hand from the motion

In fact, if you watch the video in the article, it takes you through the 3 prior iterations. Hollow clock v3 had a gear that drove the hour hand from the motion of the minute hand (which is driven from its end). The problem with that, at least with 3d printed parts, was the motion is "jerky". I built one and it never worked well. I'll be trying this version soon!