ABSTRACT
This article tells the story behind the Transmission puzzle (see Figure 1). This puzzle has a board with four pins and four gears. The object is to put the gears on the pins and make them spin freely. When solving the puzzle, you will discover that you can put any three gears anywhere and they will always spin. However, when the fourth is added, they get stuck and don’t spin anymore. So how does this puzzle work and why do the gears get stuck?
