Mechanisms—usually simple machines or a combination of simple machines—transform a specific type of motion into another type of motion. Most mechanical operations today still apply the basic science of mechanisms. Even complicated machines, like vehicle engines, still use many mechanisms to function. Some of the most widely used mechanisms include the bevel gear, bell crank, ratchet and the rack and pinion.
Bevel gears change the direction of a rotational motion. Typical bevel gears alter this rotational motion by 90 degrees, but some are designed with different degrees, depending upon the type of machinery. Typical bevel gears have two shafts that intersect into a 90-degree angle. These two shafts have toothed gears that interact with each other to transform the motion from vertical rotational into a horizontal rotational, or vice versa. Hand drills use this type of mechanism, and it changes the vertical rotational movement of the handle into a horizontal rotational movement so the chuck can drill through wood or other materials.
A bell crank changes the direction of a linear motion by using two straight bars joined together by a movable L-shaped bar with a pivot in the middle. It is named as such because it was first used to strike bells. Bell cranks can change linear movement from 90 to 180 degrees, typically focusing on 90 degrees. When one of the straight bars is pulled or pushed, the movable L-shaped bar rotates on the pivoted joint, causing the other bar to be pulled or be pushed. 90-degree bell cranks typically change a vertical linear movement into a horizontal linear movement.
Rack and Pinion
In the majority of vehicles, the steering wheel uses a mechanism known as the “rack and pinion.” It consists of two major parts: the rack, which is a straight, flat bar with a set of teeth on one of its sides, and the pinion, which is a gear with teeth connected to the rack’s teeth. This mechanism changes rotational motion into linear motion, and vice versa. When the driver rotates the steering wheel, the rack and pinion transforms this rotational movement into linear movement, changing the direction of the front wheels.
A ratchet is designed to allow linear or rotational movement but only in a single direction. It consists of a pawl and either a rack or a gear, depending on the type of movement for which it is designed. Unlike typical tooth designs found in most mechanisms, the gear or rack in a ratchet has asymmetrically designed teeth that lock into the pawl to stop it from moving in the opposite direction. The pawl has a spring and a pivot joint on one end and a tooth on the other. When a ratchet is moving in the desired direction, the pawl seamlessly slides between the teeth of the gear or rack, creating a clicking sound every time it passes a tooth. Cable ties, available in electronic shops, use ratchets as a locking mechanism to secure rolls of cables and wires.