Unusual Gear Shapes: Do They Rally Work? Videos for Engineers
We are all familiar with standard round gears, worm gears, differential gears, and orbital gears - well, maybe not as many are familiar with orbitals. These videos demonstrate how the proper geometric relationship between meshing gear sets allows just about any shape to work. While a lot of the shapes shown are curiosity objects, there are reasons for using such devices. If you imagine a pushrod attached to the output gear, you will notice that for non-round gears, there is a non-linear relationship between the constant input rotation speed of the driven gear and the output gear.
One fairly common, but not so familiar type gear is the Geneva mechanism. It is used where incremental movement at the output is required. The video below, and the animation shown to the left (click it) demonstrates how while the driven gear (green in the animation) rotates at a constant speed, the output gear (red) rotates only when the pin on the green gear engages it. During the rest of the green gear rotation, the red gear is prevented from rotating by the semicircular portion of the green gear.
If you ever have the opportunity to inspect the inner workings of an older copying machine, you'll be amazed at the complexity. If you have access to an old, mechanically driven embroidering sewing machine, note the shapes of the pattern gear sets to see how they create the complicated pattern. Increasingly, electromechanical devices are replacing purely mechanical drive systems for precision, efficiency, and cost reasons. Remember from electrical circuits class that every mechanical system has an electrical dual, it is a fairly simple matter, theoretically, to substitute some of mechanical components with electrical circuits. Mechanical engineering students are taught the same concept of duality, but from the opposite viewpoint. We like them even though their priorities are backwards ;-)