DESIGN & TECHNOLOGY
MECHANISMS
UPPER SECONDARY
MECHANISMS
INTRODUCTION TO
MECHANISMS
MECHANISMS
What are mechanisms?
Mechanisms are used to make simple machines
that make work easy.
MECHANISMS EVERYWHERE
Can you identify the mechanisms?
How did the Egyptians build the pyramid?
ANCIENT & MODERN MECHANICAL SYSTEMS
Compare between the ancient and modern
mechanical systems?
Well Water pump
Trebuchet Missile launcher Back hoe Excavator
ANCIENT & MODERN MECHANICAL SYSTEMS
TREBUCHET MISSILE LAUNCHER
DIGGING EXCAVATOR
MECHANICAL SYSTEMS
Mechanisms are mechanical systems.
A mechanical systems is used to change
one kind of movement into another.
A mechanical system has an INPUT, a PROCESS and an OUTPUT
MECHANISM
Input motion Output motion
Process
An open loop system is a one way process. The water will continue
flowing until someone close the tap.
MECHANICAL SYSTEMS
OPEN AND CLOSED LOOP SYSTEMS
Open-Loop control
PROCESS
Input Output
Turns tap Releases
water
Screw mechanism
MECHANICAL SYSTEMS
OPEN AND CLOSED LOOP SYSTEMS
Closed-Loop control
PROCESS
Input Output
Fills water Releases
waterLever
mechanism
Feedback
float is low
An closed-loop control system can respond to changes in situation
using feedback.
Toilet Cistern
Toilet cistern :
1.Cistern 2.Flapper 3.Rim 4.S-bend (S- trap)
5.Main drain 6.Float 7.Ballcock lever 8.Inlet valve
MECHANICAL SYSTEMS
Closed-Loop control(1)Cistern lever push down.
(2)Flapper lift up and release
water into (3)rim.
(6)Float will lowered down until all
water released and lift up (7)ballcock.
(7)Ballcock will let in water to fill
up the tank.
(7)Ballcock will rise as water to fill
up the tank and close again the inlet.
TYPES OF MOVEMENT
FOUR BASIC MOTIONSCircular motion Oscillating motion
Linear motion Reciprocating motion
QUIZ
Both the oscillating and reciprocating motion are
moving to and fro. What’s the difference between
the two movements that distinct them?
Oscillating is moving to and fro but at an
angular movement
Reciprocating is moving to and fro but in
linear motion.
FUNCTIONS OF MECHANISMS
The functions of mechanisms can be grouped into :
Conversion of motion Transmission of motion
Control of motion
•The speed of movement
•Transmission of motion
•Control of motion
FUNCTIONS OF MECHANISMS
Conversion of Motion
Mechanisms change one type of movement into another.
Screw mechanisms – rotary to linear motion.
FUNCTIONS OF MECHANISMS
Transmission of Motion
Mechanisms change the place of movement.
Lever-linkage mechanisms
linkage lever
Control of Motion
Mechanisms can
change the speed of movement.
FUNCTIONS OF MECHANISMS
Mechanisms can
change the direction of movement.
Gear mechanisms
Gear mechanisms
Clock
Hand drill
FUNCTIONS OF MECHANISMS
Control of Motion
Mechanisms can
change the distance of movement.
Mechanisms can
change the amount of force produced.
Screw-linkage mechanisms –
rotary to linear motion
Linkage mechanisms
Pantograph
Lifting jack
Mechanisms Activity 1
Construct a pantograph.
Challenge :
You are to construct a pantograph using the ice-cream
sticks.
Discussion :
Do the lengths of each part affect
the enlargement/reduction of the
drawing?
Duration :
10 mins
MECHANICAL SYSTEMS
MECHANISMS
MECHANICAL
CONTROL
MECHANISMS
LEVERS
MECHANICAL CONTROL
LEVERS
A lever helps us to do work. With a lever, a small input force (effort)
can create a large output force. There are 3 classes of levers and the
relationship between the effort, load and fulcrum determine its class.
E
FL
L
E
F
MECHANICAL CONTROL
LEVERS
MECHANICAL CONTROL
Classes of Levers
fulcrum fulcrum fulcrum
Force you
apply
Force you
produce
Fulcrum
L E
F LE
F
LE
F
MECHANICAL CONTROL
Examples of Levers
Wall nut cracker
2nd class
Scissor
1st class
Tweezer
3rd class
Rowing using an oar
1st class
Crowbar
2nd class
E
F
L
EF
L
EFL
E
F
LE
F
L
QUIZ
A pair of scissors is actually made up of two first
class levers. It is easy to cut a paper but not a
thick cardboard. How will you modify the scissors
so that cutting a thick cardboard is easy? Why?
Move the load closer to the fulcrum just like a pair of
snips. The shorter distance of the load to the fulcrum will
create a smaller moment. Thus less effort needed.
E F
LE
F
L
QUIZ
Is a wheel a group of 1st class levers?
Yes it is ! The 1st class levers are connected at their
common pivot and as they turn they form a wheel.
MECHANICAL CONTROL
LEVERS- Wheels and axles
A wheel and axle is a
form of a lever.
wheelaxle
MECHANISMS
LINKAGES
MECHANICAL CONTROL
LINKAGES
Levers are sometimes connected in different ways to create linkage.
LINKAGES
- Lever-linkage
MECHANICAL CONTROL
Pantograph
Tool box Scissor platform
Mechanism turn small
effort into large pushing
force.
Mechanism enlarges or reduces
sketches.
Mechanism open and close toolbox.
MECHANICAL CONTROL
LINKAGES
- Four-bar linkage
Four-bar linkage has four
connected parts.
Convert motion from :
•One type to another
•One speed to another
•One size to another
•One axis to another
MECHANICAL CONTROL
Examples of Four-bar linkage
MECHANICAL CONTROL
LINKAGES
- Types of linkage
Mechanisms Activity 2Construct a four-bar linkage.
MECHANISMS
Procedure :
Make up a four bar linkage as shown using the ice cream sticks
provided. Used the paper fasteners for the moving pivots and
drawing pins for the fixed pivots.
Discussion :
Investigate how strips of different
length affect the movement.
Duration :
10 mins
MECHANISMS
PULLEYS
MECHANICAL CONTROL
A pulley is used to transmit motion using TWO types of pulley system :
PULLEYS
Lifting Pulley System :
To lift heavy loads using rope
or chain.
Driving Pulley System :
To transfer rotary motion from one
shaft to another using belt.
MECHANICAL CONTROL
PULLEYS
Pulley
Rope
Force
Weight
Fixed Pulley• Object moves
• Pulley stays in the same spot
• Force applied only on one end of the rope
MECHANICAL CONTROL
Pulleys
- lifting pulleys
Pulley
Rope
Force
Weight
Movable Pulley• Pulley is attached to object
• Pulley and object move together
• Rope is attached to something
that does not move
• Force applied to other end of rope
Reaction
Force
MECHANICAL CONTROL
Pulleys
- lifting pulleys
QUIZ
Why do we need a fixed and movable pulley?
What’s their uses?
Pulleys help us to
do work easily .
A movable pulley
has a mechanical
advantage over a
fixed pulley.
MECHANICAL CONTROL
Pulleys
- lifting pulleys
A fixed and movable pulleys can be combined to form a compound pulley.
Advantage:
More pulleys, less effort to lift up weight.
Fixed pulley
Movable pulley
2 pulleys 3 pulleys 4 pulleys
QUIZ
What are the mechanisms used by the mobile
crane to lift up heavy objects? Do you think the
crane can lift twice its own weight?
The mechanism is a pulley system.
By using compound pulley system,
the crane can lift up weight twice its
own. But the mobile crane needed the
Support of the outrigger to anchor it to
the ground to transmit the reaction load
to the ground for stability.
Flat Belt Toothed BeltVee Belt
MECHANICAL CONTROL
Pulleys
-Belt pulleys
Advantages :
quickly and easily slid into
position over the edge of
the pulleys
can be driven at high
speeds
Disadvantages :
can not transmit large load
slipping when overloaded
Advantages :
Better grip than flat belt
(more efficient),
Can transmit larger load
than flat belt
Disadvantages :
relatively difficult to fit
slipping when overloaded
Advantages :
very little noise is produced
transmit high power load
no slipping
Disadvantages :
difficult to manufacture
MECHANICAL CONTROL
Pulleys
-Belt pulleys
Flat belt pulley
Eg. Conveyor belt
Vee belt pulley
Eg. Bench drilling
machine
Toothed belt pulley
Eg. Motorcycle gears
MECHANICAL CONTROL
Pulleys
-Open and crossed drive belt pulleys
Open drive :
pulley rotate same direction.
Crossed drive :
pulley rotate in opposite direction.
QUIZ
How can you overcome the problem of ‘slip’ for
the flat belt pulley without using other type of belt
pulleys?
Use a pulley with groove that will hold
the pulley in placed.
MECHANICAL CONTROL
Pulleys
-Driver and driven pulleys
Diameter of Driven pulley > Diameter of Driver pulley
Driven pulley turns than Driver pulley.
Diameter of Driven pulley < Diameter of Driver pulley
Driven pulley turns than Driver pulley.
MECHANICAL CONTROL
Pulleys
- Applications of pulleys
MECHANICAL CONTROL
Pulleys
- Applications of pulleys
Pulleys transmit
movement from
Motor to drum
Washing
machine
Pulleys lift and lower
weights for crane.
Gantry crane
Blinds
Pulleys raise and
Lower sails and
blinds.
If both pulleys are of the same diameter,then they will rotate at the same speed.
When one pulley is larger than another, thenmechanical advantage and velocity ratio
are introduced.
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)
MECHANICAL CONTROL
Mechanisms are often used to allow a small effort to move a
large load. This property is called Mechanical Advantage (MA).
Mechanical advantageis calculated by dividingthe load by the effort.
Mechanical Advantage(MA) & Velocity Ratio(VR)- Mechanical Advantage
Mechanical Advantage = Output = Load
Input Effort
MECHANICAL CONTROL
Mechanisms are used to translate a small amount of movement into
a larger amount. This property is known as Velocity Ratio (VR).
It can be calculated by dividing
the movement of the effort by
the movement of the load.
Mechanical Advantage(MA) & Velocity Ratio(VR)
- Velocity Ratio
Velocity Ratio = Input = Distance moved by Effort
Output Distance moved by Load
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)
- EfficiencyIn an ideal world, mechanical advantage and velocity ratio would always
be equal to each other. In reality, because of friction, air resistance, this
ideal situation would never be achieved.
We said the system is not 100% efficient.
Efficiency = Mechanical Advantage X 100%
Velocity Ratio
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Mechanical Advantage for Lifting Pulley System
No. of Pulley = 2 No. of Pulley = 4No. of Pulley = 3
MA = 2 MA = 3 MA = 4
Mechanical Advantage (MA) = No. of Pulleys
QUIZ
How many pulleys are used to raise the shelter
and its mechanical advantage?
3 pulleys are used. M.A. = 31st
pulley
2nd
pulley
3rd
pulley
You can also count the no. of
rope lifting the load equal to no.
of pulleys.
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Mechanical Advantage for Lifting Pulley System
Mechanical Advantage (M.A) = No of pulleys
= 4
M.A = Output = Load
Input Effort
4 = 200
Effort
Effort = 200 = 50 N
4
Mechanical Advantage = Output = Load
Input EffortEffort
Load
200N
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Mechanical Advantage for Lifting Pulley System
Effort
Load
Mechanical Advantage (M.A) = No of ropes supporting load
= 4
Effort = 50 N
200 N
Each rope will exert an effort of F Newton.
F + F + F + F = 200
4 F = 200
F = 200
4
= 50 N
200N
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Mechanical Advantage for Lifting Pulley System
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Velocity Ratio for Lifting Pulley System
Velocity Ratio = Input = Distance moved by Effort
Output Distance moved by Load
10cm
40cm
VR = 40 = 4
10
In order to lift the 200 N load with a small
effort of 50 N, the effort of pulling the rope
will have to move 4 times longer than the
distance lifted for the load.
10cm
40cm
Effort
Load
200N
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Velocity Ratio for Lifting Pulley System
MECHANICAL CONTROL
Mechanical Advantage(MA) & Velocity Ratio(VR)- Efficiency for Lifting Pulley System
Efficiency = Mechanical Advantage X 100%
Velocity Ratio
Efficiency = MA x 100%
VR
= 4 x 100
4
= 100 %
MA = 4
VR = 4
This is a perfect condition but in reality the efficiency will be less
than perfect due to friction.
Effort
Load
200N
QUIZ
The same 4 pulley system is used to lift up 200 N of
load. But when the effort was measured it showed 60
kg more than in ideal condition. What’s the efficiency
and why is the effort higher than calculated?
VR = No of pulleys
= 4
MA = Load
Effort
= 200
60
= 3.33
Efficiency = MA x 100
VR
= 3.33 x 100
4
= 83.3 %
A higher effort is needed to overcome the
frictional force between the rope and the
pulley during lifting.
Effort
60N
Load
200N
MECHANICAL CONTROL
Velocity Ratio(VR)
Velocity Ratio (VR) is the relationship between the input and
output movements in a mechanical system. It is also known as
Transmission Ratio (TR).
Output movement
Input movementVelocity Ratio =
The ratio can be used to compare distances, angles or number of revolutions.
MECHANICAL CONTROL
Velocity Ratio(VR)- Velocity Ratio for Belt Pulley System
motor
DriveR pulley
DriveN pulley
dia. of DriveR pulley
dia. of DriveN pulley
Output Speed
Input SpeedVelocity Ratio = =
MECHANICAL CONTROL
dia. 200 mm
dia. 40 mm
Motor,
1500 rpm
Drum
Velocity Ratio(VR)- Velocity Ratio for Belt Pulley System
Velocity Ratio = dia. of DriveR pulley
dia. of DriveN pulley
1
5
Output speed
Input speed=
= =40
200
1
5
5
1500Output speed =
= 300 rpm
QUIZ
Both MA and VR are ratio of their output to input. But
for a belt pulley, why the VR in terms of pulley diameter
is input diameter to output diameter and sometimes
the opposite?
MA = Output force
Input forceVR = Input movement
Output movement
Input speed
(Driver)
Output speed
(Driven)Output speed
(Driven)
Input speed
(Driver)
Ø input Ø output Ø input Ø output
VR is inversely proportional to Ø input / Ø output
VR = Ø Output / Ø Input
Input speed/output speed = Ø Output / Ø Input
MECHANISMS
CAMS
MECHANICAL CONTROL
CAMS
A cam is a specially designed and shaped piece of material that rotates,
causing a lever or rod to move.
MECHANICAL CONTROL
CAMS
- Rotary camsThe THREE common type of cams :
Pear Snail Eccentric
The cam-and-follower converts circular movement to a kind of oscillatory
motion. It cannot work the other round.
MECHANICAL CONTROL
CAMS
- Pear shaped cam
The follower remains motionless for about
half of the cycle of the cam and during the
second half it rises and falls.
follower
pear shaped cam
slide
CAMS
- Pear shaped cam
MECHANICAL CONTROL
Dwell
Dwell is the period when the follower does not move
MECHANICAL CONTROL
CAMS
- Snail shaped cam
Disadvantage : Rotating in a clockwise
direction would probably lead to the entire
mechanism jamming.
A snail drop cam is used where the drop
or fall of the follower must be sudden.
MECHANICAL CONTROL
CAMS
- Snail shaped cam
MECHANICAL CONTROL
CAMS
- Eccentric cam
An eccentric cam is a disc with its centre of
rotation positioned ‘off centre’. This means
as the cam rotates the flat follower rises
and falls at a constant rate.
MECHANICAL CONTROL
Cams
- Eccentric cam
MECHANICAL CONTROL
Cams
- Distance and rotation graphs
MECHANICAL CONTROL
CAMS
-Applications of cams
Cam key lock
MECHANICAL CONTROL
CAMS
-Applications of cams
Cam operated
pushchair brake
Cam timer
Internal combustion engine
QUIZ
A local toy shop has asked you to design a
model to encourage parents to buy their young
children mechanical toys. The partially made
model is seen opposite. Add a suitable cam that
controls two followers so that they rise and fall.
As the swash cam rotates the
Followers move up and down
alternately. The swash cam
operates like a ‘spinning top’.
The followers move the arms
of the model up and down as
if it is waving.
MECHANICAL CONTROL
GEARS
MECHANICAL CONTROL
GEARS
MECHANICAL CONTROL
GEARSA gear is a wheel with teeth around its edges. Gears can be combined in
different ways to :
- Control speed
- Increasing turning force
- Changing direction of motion
Spur gear Worm gear Bevel gear
Gears are used to transmit power and motion.
MECHANICAL CONTROL
GEARS
- Spur gears• Two gears meshes together
• Both gears rotate in opposite directions
to each other
How do you make the spur gears rotate
in the same direction?
Add idler gear
MECHANICAL CONTROL
GEARS
- Spur gears
MECHANICAL CONTROL
GEARS
- Spur gears• Several spur gear meshes together form GEAR TRAIN.
GEAR TRAIN
Gear train has a driver and driven gear.
Driver gear is connected to a motor to drive the driven gear.
MECHANICAL CONTROL
GEARS
- Gear ratio
MECHANICAL CONTROL
GEARS
- Gear ratio
No of teeth on DriveR gear
No of teeth on DriveN gearGear Ratio =
Note : Gear ratio is also known as Velocity Ratio (VR)
MECHANICAL CONTROL
GEARS
- Gear train and Compound gear train• make large speed change
• increase or decrease the torque (turning force)
QUIZ
How do you increase the gear ratio of a spur
gear without replacing any of the gears?
You can increase or decrease
the gear ratio by adding gears
to form a compound gear train.
MECHANICAL CONTROL
GEARS
- Bevel gears• to transmit motion through 90⁰
GEARS
- Worm gear
MECHANICAL CONTROL
• to turn a worm wheel
•reduce speed considerably but increase turning force
•worm gear has only ONE tooth.
•Worm gear is a ONE-WAY drive system
If worm wheel has 50 teeth, worm gear
must rotate 50 times.
MECHANICAL CONTROL
GEARS
- Applications of worm gear
MECHANICAL CONTROL
GEARS
- Applications of gears
MECHANICAL CONTROL
CRANKS
MECHANICAL CONTROL
CRANKSA cam is an arm that has one end connected to a shaft.
MECHANICAL CONTROL
CRANKS
- Cranks and slider
Cranks and slider converts
movement from circular to
reciprocating motion or the
other way round.
MECHANICAL CONTROL
CRANKS
- Applications of cranks
Sheet metal roller Piston engine
MECHANISMS
RACK-AND-PINION
MECHANICAL CONTROL
RACK & PINION MECHANISMSThe rack-and –pinion mechanism consists of a straight toothed ‘rack’ that
meshes with a toothed wheel called a ‘pinion’.
Rack-and-pinion mechanisms – rotary to linear motion.
Rack
Pinion
Rack
MECHANICAL CONTROL
RACK-AND-PINION
-Applications of rack-and-pinion
Railway track Car steering wheel Bench drilling machine
QUIZ
How does a train manage to climb up a steep
slope and a forklift able to lift heavy things?
By using the rack and pinion.
MECHANISMS
RATCHET-AND-PAWL
MECHANICAL CONTROL
RACHET & PAWL MECHANISMSThe ratchet & pawl mechanism allows movement in one direction but not
the other.
Spring-loaded
The pawl allows the teeth to move one way but the other.
MECHANICAL CONTROL
RATCHET & PAWL MECHANISMS
- Applications of ratchet & pawl
Ratchet Fishing reel
MECHANISMS
SPRING-LOADED
MECHANISMS
MECHANICAL CONTROL
SPRING-LOADED MECHANISMSSprings store elastic energy that can be released to provide a return
movement in mechanisms.
Air pumpClockwork motor
The spring can be used in tension or compression.
Spring in compression
Spring in tension
MECHANICAL CONTROL
SPRING LOADED MECHANISMS
- Compression and Tension Spring
A compression spring is used to resist a squashing force
or compressive force.
A tension spring is used to resist a stretching force
or tensile force.
MECHANICAL CONTROL
SPRING LOADED MECHANISMS
- Torsion and Flat Spring
A torsion spring is used to resist
a turning force or torque force.
A flat spring is a piece of material
that returns to its original shape
when bent.
MECHANISMS
SCREWS
MECHANICAL CONTROL
SCREWA screw is a ramp wrapped around a cylinder. It can produced a very large
force.
Screw mechanisms – rotary to linear motion
MECHANICAL CONTROL
SCREW
MECHANICAL CONTROL
SCREW
- Applications of screw
CABLE CONTROL
MECHANISMS
MECHANICAL CONTROL
CABLE CONTROLCable allow things to be controlled from some distance away.
- operated with pedal or lever
- wound on rotating drum
Cable work well in tension for pulling things.
MECHANICAL CONTROL
CABLE CONTROL
- Applications of cable control
Concrete has HIGH compressive strength but LOW tensile
strength. When a heavy load is placed on a concrete beam, the
bottom is likely to crack as it is in tension. Therefore Engineer’s
overcome the low tensile strength of the concrete by adding
reinforcement steel bars along the tensile stress area.
QUIZ
Why do concrete structures have metal bars
(reinforcements) inside them?
Activity
Build and test different shape of beams using papers
by folding. Find out which shape is the strongest.
Try the activity worksheet to find the answer!
MECHANICAL CONTROL
QUIZ
A thin sheet of wood usually breaks easily
along its grain. However, if a few sheets of
wood are glued together with their grains at
900 to one another, this will caused the
completed structure to be stronger.
The layers of ply with the grains at 900 to one another created
an interlocking system that make it strong.
MECHANICAL CONTROL