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:
Here’s the ever-popular jumping spider. This one goes in a little more of a horizontal direction.
And here’s a peek at the four-bar mechanism for the jumping spider…
Here’s a setup using rotary motion to activate the four-bar linkage which makes a kinder, gentler Halloween ghoul. He mistakenly calls it a 2-bar mechanism but I think we can forgive him for that. Can you spot the 4th bar? (It’s the chain).
And here’s a use of a 4-bar mechanism in a cute greeting card:
Four-bar linkages are used in all sorts of more sophisticated engineering design. If you want to see some hard-core uses, check out this Wikipedia page.