MECHANISMS THAT CONTROL MOTION

DIRECTION CONTROL: ratchets
A rachet is a mechanism that controls the direction of motion. It allows motion in one direction, but not in the other.

SPEED REDUCTION: brakes

Brakes use friction to reduce speed and they are activated by levers that transmit force to an output receptor, which put pressure on the wheel. This produces friction, and slow down the wheel.

There are various types of brakes according to where the friction is produced:

Disc brake

Band brake

Drum brake

⇨Disc brakes: A disc is connected to an axle. Brake pads apply pressure to the disc.

⇨Band brakes: A drum is connected to an axle. A flexible band applies pressure to the outside of the drum.

⇨Drum brakes: A drum is connected to the axle. A pair of brake shoes apply pressure to the inside of the drum.

  ⇒TRANSFORMATION OF MOTION⇐

ROTARY-LINEAR TRANSFORMATION

WHEEL

Wheels reduce contact with the ground and decrease friction. If there isn't enough friction, they can slide out of control. We need less force to move vehicles with larger wheels and they move more quickly.

RACK AND PINION

This mechanism has two parts: the rack is a bar with many theeth and the pinion is a gear with theeth that interlock with the rack. It transforms rotary motion into linear motion.

NUT AND BOLT

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

WINCH AND CRANK
It is a cylinder that rotates around a horizontal axis. We turn the crank to rotate the winch. The crank increases the force and the winch transforms rotary motion into linear motion. This mechanism has the Law of the Lever.

RECIPROCATING ROTARY-LINEAR TRANSFORMATION

CRANKSHAFT

We can conect multiple rods to one shaft. The rods are connected to cranks, and the cranks are connected to the crankshaft. It can synchronise the movements of various parts.

CAM

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

When we put multiple cams on a shaft, it's called a camshaft. We can use it to synchronise the movements of various parts.

ROTARY TRANSMISSION

Rotary transmission systems put two rotating elements into contact. These mechanisms have two purposes:
⇒Transferring rotary force to an input location to another location.
⇒Changing the rotary speed by using rotating elements of different sizes.
There are various mechanisms:

    

Pulleys with belts

Friction wheels

Interlocking gears

Sprockets with chains

 

Here, the most reliable mechanism is the interlocking gears, because they don't slip easily.

CHANGES IN SPEED

We can increase, decrease and make constant the speed with these systems:

  

Decreasing and  Increasing speed system

Cosntant speed system

SPEED RATIOS

The relationship between the speeds of the two wheels is inversely proportional to their sizes. 

                                      

                         N2/N1=D1/D2

The relationship is called the ratio of transmission, where N is the speed of relation and D is the diameter of the wheel. 

BELT DRIVES AND GEAR TRAINS  

-Wheel 1 turns wheel 2, wich moves faster because it is smaller. If wheel 1 makes 1 rotation, wheel 2 makes 1.5 rotations.

-Wheel 2 and wheel 3 are connected to the same axis, so they turn together.

-Wheel 3 turns wheel 4, wich moves faster because it is smaller. If wheel 3 makes 1.5 rotations, wheel 4 makes 3 rotations (1.5x2=3)

                      N4/N1=D1XD3/D2XD4

CHANGES IN DIRECTION AND ROTATIONS

We can change the direction of the rotation by using belts in different possicions or different axis.

Parallel axes

Perpendicular axes

Different posicion of the belts

Crossed axes

 








WORM DRIVE
A worm drive reduces the speed of rotary system very well. It has two parts: a worm shaft and a worm gear. The shaft has more than one groove. Each groove interlocks with one of the worm gear. This mechanism is not reversible.

LINEAR TRANSMISSION OF MOTION

Levers

A lever is a rigid bar that truns around  point called fulcrum. Various forces may act on the lever at the same time. When the forces acting on opposite ends of a lever are equal, we say the lever is in equilibrium. We can express this mathematically as the Law of the Lever:

                                       F x d = R  x r                            

CLASSES OF LEVERS

A HAND CRANK

It has two parts, one is connected to a rotating shaft and the other forms a handle. We can use a hand crank to apply force at a distance from the axis of the shaft. It has the Law of the Lever.

Class 2 lever

PULLEYS AND COMPOUND OF PULLEYS SYSTEMS

In a system of pulleys, equilibrium between the forces depends on the path that the rope follows.

PULLEYS

A pulley is a wheel that rotates around an axis and has a groove. We use this mechanism to apply less force. There are two basic pulleys:

Fixed pulley (F=R)

Movable pulley (F=R/2)

                                                     

COMPOUND PULLEY SYSTEMS

This is a special combination of fixed and movable pulleys.The more pulleys we have, the mechanism is more complex, but  it is easier to lift the load.

    

  Vertical and Exponential systems

Horizontal System

CLASSIFICATIONS OF MECHANISMS 

Rotary transmission

Transmision of motion
* Linear transmission⇒ puley
* Rotary transmision⇒ gears

Linear transmission

Transformation of motion

* Rotary-linear⇒ rack and pinion

* Reciprocating rotary-linear⇒ crankshaft

Rotary-linear

Reciprocating rotary-linear

                                           

                     

Motion control

* Direction control⇒ ratchet

* Speed reduction⇒ brake

Speed reduction

Direction control

Energy accumulation
* Absorption/Dissipation⇒ spring

Connection
*Linkage⇒ clutch
*Support⇒plain bearning

Linkage (clutch)

Support (plain bearning)

CONSERVATION OF ENERGY AND WORK IN MECHANISMS
Mechanisms can´t create energy on their own. All mechanisms produce the same amount of work that is done to them, including energy that is lost to friction and heat.
If a mechanism increases force, it must decrease motion, in this way, energy and motion are conversed.

 MECHANISMS

WHAT IS A MECHANISM?

A mechanism is a device designed to transform input forces and movement into an output force and motion.

Mechanisms transmit and transform force and motion from an input source, to an output receptor.In the case of a bicycle the input source is our legs.

                               

                               

THE PARTS OF A MECHANISM

                      Input of force and motion
                                      ⇩
                               Mechanism
                                      ⇩
                      Output force and motion

BLOGS
Blogs are a special type of web page. Many blogs are opinion generator about a variety of topics. Other blogs are used as 'online diaries' for people.

Bloggers publish entries in chronological order, with newer posts appearing at the top of the list. People can write a comment with their opinion as well.

Tumblr, Wordpress and Blogger are some of
the most popular weblogs.

WIKIS

A wiki is a collection of web pages that visitors can edit, modify or expand.

 Adding new content to a wiki page is easy:

Other example of wiki

1.-Click in the Edit button.

2.-Write a new contribution.

3.-Click in the Save button.

An example of wiki

WIKIPEDIA

Wikipedia is a universal encyclopedia with no restrictions on use, modification or redistribution. Anyone can contribute their knowledge to this project.