5 MECHANISMS THAT CONTROL MOTION

5.1. Direction control: Ratchets

 A ratchet is a mechanism that controls the direction of motion. It allows motion in one direction, but not in the other, as you can use the picture.

5.2. Speed reduction: Brakes

Brakes use friction to reduce speed. They are activated by certain levers. The lever transmits force to an output receptor, which puts pressure on the wheel.

 The types of brakes are:

Disc brakes:

 

Band brake:

Drum brake:

4.2. RECIPROCATING ROTARY - LINEAR TRANSFORMATION

The pedal mechanism of a bicycle transforms the reciprocating movements of our legs into continuous rotary motion. In a similar way, the pistons of a car engine produce a reciprocating linear motion that turns the wheels.

Crank and rod mechanism

The piston moves a rod forward and backward. This rod turns the first wheel. The second wheel turns because it's connected to the first wheel by another rod.

USES: This mechanism was important for the fist steam engines.

Crankshaft mechanism

We can connect multiply rods to one shaft. The rods are connected to cranks, and the cranks are connected to the crankshaft.

USES: We can use crankshaft for combustion motors that use pistons.

Cam mechanisms

A cam is an irregulary shaped device that rotates on a shaft. When the cam rotates, it pushes a special bar called a follower. The follower can move other parts or it can turn a switch on and off.

We can put multiple cams on one shaft, called a camshaft. We can use it to synchronize the movements of various parts, such as the valves of an internal combustion motor.

USES: We can find camshafts in toys, automatic tools and combustion motors.

USES: There are often eccentric cams in sewing machines and other devices that transform rotary to linear motion.

4.1. ROTARY-LINEAR TRANSFORMATION

Wheel

With each rotation, a wheel moves forward a distance that is equal to its circumference(2 times PI times R). As a result, we need less force to move vehicles with larger wheels and they move more quickly.

Rack and pinion mechanism

A rack and pinion mechanism has two parts. The rack is a bar with many teeth and the pinion is a gear with teeth that interlock with the rack.

Nut and bolt mechanism

A nut and bolt mechanism transforms rotary motion into linear motion. It has two parts: a bolt of shaft with a spiral groove and a nut that turns around it.

USES: We use it to hold things together. We can also fin them in scissor jacks for lifting cars, water tap mechanisms and screw-top bottles.

Winch and crank mechanism

A winch is a cilinder that rotates around an horizontal axis. We attach a rope to the winch and to a load. Then we turn the crank to rotate the winch. The rope rolls up around the winch and lifts the load.

F x d = R x r

We use winch and crank mechanism to lift or pull heavy loads.