This gear drive was a new one on us ... ball-screw actuator could (and WAY more engagement than a simple pinion moving a rack), so the forces it can control are greater—sufficient to steer ...

Figure 1.1.6: The green gear with only five teeth has a severe undercut, which weakens its teeth. This undercut is necessary to avoid interference with the teeth from the other gear during rotation.

Different gears like spur, bevel, worm and wormwheel, rack and pinion, meshed gears, and threaded bars serve various purposes. When selecting a gear system, consider speed, direction, force ...