I spent a couple of hours this morning learning more about mechanical linkages on YouTube — specifically four-bar linkages (sometimes stated as 4-bar). These little beauties are in lots of places that I hadn’t thought too much about. For instance, they’re used in adjustable desk lamps that clamp to the edge of your desk, car steering, windshield wiper mechanisms, oil derricks, locomotive wheel drives, and many more places.
The first place I ever conciously experienced a four-bar linkage was in a Halloween prop often called a pop-up or grave popper. This is where some sort of monster pops up from behind a gravestone to scare the sugar out of any unsuspecting Trick-or-Treater!
Here’s an example of the four-bar linkage powering a vertical Halloween pop-up: