Mechanical Systems and Motion Transmission Principles

Classification of Mechanisms

Transmission of Motion

• Linear transmission: lever, pulley, block and tackle
• Rotary transmission: friction wheels, belt drive, gears

Transformation of Motion

• Rotary to linear: wheel, rack and pinion, nut and bolt
• Reciprocating: crank and rod, crankshaft, cam

Motion Control

• Direction control: ratchet, freewheel
• Speed reduction: brake

Energy Accumulation

• Absorption/dissipation: spring

Connection

• Linkage: clutch
• Support: plain bearing

Levers

Class 1: Levers can do both of those things; the fulcrum is between the force and resistance.

Class 2: Levers increase the force that we apply; the resistance is between the fulcrum and the force.

Class 3: Levers increase the distance that the end of the lever moves; the force is between the fulcrum and resistance.

Rotary Transmission

All of these mechanisms keep the same speed ratios, but each one offers a different advantage. Metal chains are stronger and last longer than rubber or plastic belts.

Worm Drive

A worm drive reduces the speed of a rotary system very effectively.

Rotary to Linear Transformation

Wheel

Wheels are essential parts of bicycles. They move more easily because they reduce our contact with the ground and decrease friction.

Rack and Pinion

The rack is a bar with many teeth and the pinion is a gear with teeth that interlock with the rack. These are commonly used in sliding doors.

Nut and Bolt

These transform rotary motion into linear motion. They consist of a bolt or shaft with a spiral groove and a nut that turns around it.

Winch and Crank

A winch is a cylinder that rotates around a horizontal axis. We attach a rope to the winch and to a load. The crank rotates the winch.

Reciprocating Rotary and Linear Transformation

Crank and Rod

This mechanism was important for the first steam engines. Today, we find cranks and rods in internal combustion engines, as well as windscreen wiper mechanisms.

Crankshaft

We can connect multiple rods to one shaft. The rods are connected to cranks, and the cranks are connected to the crankshaft. Crankshaft mechanisms can synchronize movement.

Cam

A cam is an irregularly shaped device that rotates on a shaft. When the cam rotates, it pushes a special bar called a follower. These are often found in toys.

Motion Control Mechanisms

Ratchets

A ratchet is a mechanism that controls the direction of motion. It allows motion in one direction, but not in the other. These are used in watches.

Brakes

Brakes use friction to reduce speed. They are activated by some type of lever.

• Disc brakes: A disc connected to an axle.
• Band brakes: A drum connected to an axle.
• Drum brakes: A drum connected to an axle.

Energy Accumulation: Springs

Springs are flexible devices that absorb energy when we apply force to them. They are used in items like beds and sofas.

• We push a compression spring.
• We pull on a traction spring.
• We bend a torsion spring.

Bearings and Support

The support that holds a rotary shaft is called a bearing. It keeps the shaft in position.

Plain bearings are formed by two rings. One of the rings is connected to the rotary shaft and the other is connected to the support.