MECHANISMS
INTRODUCTION
Early man discovered that work could be made easier by using a
mechanical device to control movement and force rather than his bare
hands. Today mechanisms are an integral part of our lives, so much so
that we take them for granted. However complex, all mechanisms have
two things in common:
1.
2.
An input motion and force
An output motion and force
Consider the mechanical devices below:
Page 1
DEFINITION
A mechanism is a device which changes an input motion and force into a desired output
motion and force.
INPUT
MOTION
& FORCE
MOTION
MECHANISM
OUTPUT
MOTION
& FORCE
There are four principal types of motion:
1.
2.
3.
4.
Linear
Reciprocating
Rotary
Oscillating
Linear Motion
This is motion in a straight line and can
be represented by an arrow like this:
Although the wheels of the bicycle in the picture above are going around,
the overall motion is linear in nature as the man moves forward along the
road.
Reciprocating Motion
This is forward and backwards motion
in a straight line. It can be represented
by a double arrow like this:
The engine piston opposite reciprocates up
and down continuously. It does not move at
a constant speed as it has to change
direction at the highest and lowest
positions.
Engine crankshaft and
piston
Rotary Motion
This is motion in a circular direction and
may also be called circular motion. It is
a very common form of motion and can
be represented by a curve with an
arrow head like this:
The chuck of a drill moves in
a circular motion
Page 2
Oscillating Motion
Oscillating motion is essentially
reciprocating motion along an arc. It
can be represented by an arc with an
arrow head at both ends.
A common example is the pendulum in a clock which oscillates continuously
back and forth. In this case the pendulum is instrumental in the time
keeping of the clock. A child on a swing moves back and forth through an
arc as the swing hangs from a pivotal point.
The input and output motions associated with particular mechanisms may
or may not be the same. Consider the examples below:
The paper punch has both a
linear input and a linear output
motion
THE WEDGE
The T-Bar clamp has a rotary input
motion and a linear output motion
Generally mechanisms are used to afford
the user a mechanical advantage. In other
words by putting in a small force we can
get a larger force “out”. The wedge is one
of the earliest known mechanisms known
to man which afforded him this
advantage. From splitting logs to pulling
loads up a ramp the wedge or “inclined
plane” became one of early mans best
friends.
Wedge
Inclined Plane
Page 3
Calculations
Effort
Velocity Ratio
Consider the man opposite
pulling a load up the inclined
plane. The velocity Ratio
produced by this inclined plane h
can be found using the
formula:
Velocity Ratio =
Load
Distance moved by effort
Distance moved by load
If the length of the ramp is “s” and the height is “h” then the man must
pull the load a distance of “s” in order to raise it through the height “h”.
Hence the Velocity Ratio = s/h
If for example s = 10m and h = 4m then the Velocity Ratio = 10/4 or 2.5
In this way the man must move his effort force 2.5 time further than the
load is lifted. In doing this he gets a Mechanical Advantage. It can be
shown that this mechanical advantage is also 2.5 (ignoring frictional
forces in the wheels of the cart).
Mechanical Advantage =
Load
Effort
=
s
h
If the load in this example was 1000N then the effort force would be 2.5
times smaller, i.e. 400N
We can learn from this that if the effort is moved over a greater
distance than the load then the effort force will be smaller than the load
and a mechanical advantage is afforded to the person doing the work.
This mechanical advantage is “paid for” by the person having to move
his/her smaller force over a greater distance (2.5 times more in this
example).
Screw Threads
If an inclined plane type triangle is wrapped around a
cylinder the long edge of the triangle produces a
helix. This is the curve which is used in the
manufacture of screw threads. Screw threads
produce considerable mechanical advantage due mainly
to the shallow angle at which the helix slopes.
Helix
Consider the car jack opposite. By using a crank handle to turn the
threaded bar of the jack the jack rises thereby lifting the vehicle. The
distance moved by the effort is considerably greater than the height
through which the car rises. Hence the velocity ratio is very high and so
too the mechanical advantage. The screw thread plays a large roll in
converting the small input force of the person’s hand into a large output
force at the top of the jack.
Page 4
Drill vices are very useful items in a
workshop. By turning the handle of
the vice very large forces can be
applied to the object in the vice
thereby securing it while it is being
drilled. The lever handle and the
screw thread combined are
responsible for the mechanical
advantage afforded by the vice.
LEVERS
Drill Vice
A lever is a rigid rod pivoted about a fixed point/axis called a
fulcrum.
Levers may be used to produce a small output motion from a large input
motion. In so doing the output force will be much greater than the input
force, hence producing a mechanical advantage. The brake on the soapbox cart and the car handbrake illustrate this use of a lever.
Large movement
Small force
Large movement
Small force
Small movement
Large force
Small movement
Large force
Levers as force amplifiers
Velocity Ratio
As with the inclined plane the ratio of the amount of movement made by
the effort to that amount made by the load is called the Velocity Ratio.
Distance moved by effort
Distance moved by load
Velocity Ratio =
If in the illustration below the man pushes the lever down a distance of
1m and the load rises by 0.5m, then the Velocity Ratio is:
Load
1
0.5
Effort
= 2
Load
Effort
Fulcrum
Lever Diagram
Fulcrum
Assuming that the lever in this example does not bend and there is no
friction at the fulcrum, then the Mechanical Advantage will be equal in
value to the Velocity Ratio. In other words if the weight is 1000N then
the effort force will be 500N (the weight of the lever is ignored in these
basic calculations).
Page 5
LEVER TYPES
Levers are divided into three classes depending on the relative positions
of the load, effort and fulcrum. The lever diagrams below illustrate these
three classes:
Effort
Effort
Effort
Fulcrum
Fulcrum
Fulcrum
Load
Load
Load
Class 1
Class 2
Class 3
Provided the effort is further from the fulcrum than the load in the
Class 1 lever, the Velocity Ratio will be greater than 1 and consequently
the Mechanical Advantage will be greater than 1.
In the Class 2 lever the Mechanical Advantage will always be greater than
1 as the effort is always further from the fulcrum than the load.
In Class 3 there is a Mechanical disadvantage as the load is further from
the fulcrum than the effort. To balance the lever the effort force must
be greater than that of the load.
A practical example of each of the three classes is given below:
E
E
F
E
L
F
F
L
L
E
Class 1
MOMENTS
Class 2
Class 3
Consider a person’s hand applying a
force to a spanner as shown
opposite. The product of the effort
force and the distance from the
effort force to the fulcrum (a nut in
this case) is referred to as a turning
moment or simply a “moment”. It is
measured in Newton metres (Nm).
The Law of the Lever (Principle of Moments)
The Law of the lever tells us that when a lever is in equilibrium the sum of
the clockwise moments is equal to the sum of the anti-clockwise moments.
Sum of clockwise moments = Sum of anti-clockwise moments
Page 6
PROBLEM
The diagram illustrates a lever
microswitch. The spring loaded button
of the microswitch exerts a force on
the lever at the point of the button
amounting to 0.5N. Calculate the effort
force required to depress the lever and
so activate the switch.
5mm
45mm
E
F
L
0.5N
The Law of the Lever tells us that the:
Note:
Always
convert
dimensions
to metres!
Sum of the clockwise moments = the sum of the anti-clockwise moments
Hence: E x 0.05 = 0.5 x .005
⇒ E x 0.05 = 0.0025
⇒ E = 0.0025/.05
⇒ E = 0.05N
The result tells us that the effort force is ten times smaller than the load
force. This makes sense since the effort force is acting over a distance
ten times greater than the distance over which the load is acting.
LINKAGES
A linkage is an assembly of components (generally linear in form) which
are designed to act together and allow forces and motion to be
transmitted to where they are needed. There is an input force and motion
and an output force and motion. The output force may be bigger or
smaller than the input force and it may have a different direction. The
input and output motion may differ in a similar manner. The examples to
follow illustrate some of the basic types of linkages:
Center
Pivot/fulcrum
Input motion and force
is equal in size to the
output motion and
force. The Mechanical
Advantage and Velocity
Ratio are therefore
equal to 1
Offcentre Pivot
In this case the input
motion is greater than
the output motion,
however the output
force is greater than
the input force. Given
that the input is the
effort and the output
the load, the Velocity
Ratio and Mechanical
Advantage will be
greater than 1
Input
Parallel Linkage
Pivot
Output
In a parallel motion linkage the opposite sides of
the parallelogram remain parallel even when it is
pushed out of shape. The lazy-tongs below uses
this principle to good effect as it stretches in
length as the handles are brought closer together.
It is used to pick up objects which are dangerous
or inaccessible.
Output
Pivot
Input
Reverse Motion Linkages
Lazy-tongs
Page 7
Bell Cranks
The calliper brakes of a bicycle illustrate the
use of bell crank levers to change a pull into a
push and take motion around a corner. The
brake cable, when pulled causes the bell cranks
to move in opposite directions and to push the
brake blocks against the wheel rim. The friction
generated brings the bicycle to a halt.
Treadle Linkage
This linkage can convert oscillating
motion into rotary motion and vice
versa. Old foot operated sewing
machine used this mechanism.
PULLEYS
One of the methods used in technology to transmit motion and torque
between parallel shafts is to use a pulley and belt drive. A pulley is a
wheel with a grooved rim .
Pulley
wheels
Parallel
shafts
Graphic symbol for a pulley drive
Motor
Consider the pulley drive opposite. The
motor has a large pulley wheel mounted
on its shaft and this in turn is driving a
small pulley which is mounted on a shaft
which is parallel to the motor shaft. The
Driver
pulley on the motor shaft is referred to
as the driver (“effort”) and the other
pulley is referred to as the driven
(“load”). In this case the driven pulley
Driven
must be rotating faster than the driver.
If the driver has a diameter of 80mm and the driven pulley diameter is
40mm then the driven will rotate at twice the speed of the driver but
with only half the torque. We are already familiar with the formula:
Velocity Ratio = Distance moved by effort
Distance moved by load
Since the diameter of a wheel is directly proportional to its
circumference the formula for Velocity Ratio must be:
Velocity ratio = Diameter of driven pulley
Diameter of driver pulley
= 40mm = 1:2
80mm
This means that one revolution of the driver produces two revolutions
of the driven. Hence the driver rotates at half the speed of the driven.
Page 8
VELOCITY
If the rotary velocity of the motor in the previous example is 1000
revs/min what then is the rotary velocity of the driven pulley?
Solution: Common sense tells us that if the driver rotates at half
(Velocity ratio = ½) the speed of the driven then the driven speed must
be 2000 revs/min.
A formula is generally used to calculate the driven speed.
Rotary Velocity of driven pulley = Rotary velocity of driver
Velocity Ratio
= 1000/0.5 = 2000 revs/min
Consider the pulley arrangement opposite.
If the rotary velocity of the driven pulley is
300 revs/min, calculate the rotary velocity
of the motor shaft.
Driver
Pulley
30mm dia.
Velocity ratio = Diameter of driven
Diameter of driver
= 75
= 2.5
30
1
From the formula above:
300
= Rotary velocity of driver
2.5/1
Driven pulley
75mm dia.
⇒ 300 x 2.5 = Rotary velocity of driver
⇒ Rotary velocity of driver = 750 revs/min
Jockey Pulleys
A problem which may arise with pulley
drives is that any slackness in the belt
may cause the belt to slip. To
overcome this problem a jockey pulley
is often used. This pulley engages with
the belt as shown opposite and keeps
the belt in firm contact with the
driver and driven pulleys. They are
used on many belt drives such as in the
band-saw of your school workshop.
CHAIN &
SPROCKET
Another method of transmitting motion
and torque between parallel shafts is to
use a chain and sprocket mechanism.
This system provides a non-slip positive
drive due to the traction between the
chain and the sprockets. Chain and
sprockets are used widely in technology,
the most common example being the
chain drive on a bicycle.
Jockey Pulley
Chain
Sprocket
Page 9
PROBLEMS
Velocity Ratio
To calculate the Velocity Ratio for a chain
and sprocket drive the number of teeth on
the gears must be taken into account.
Driven
20 teeth
Driver
30 teeth
V.R. = Number of teeth on driven sprocket
Number of teeth on driver sprocket
In the example opposite the Velocity Ratio is:
V.R. = 20/30
⇒ V.R. = 2/3 or 2:3
If the rotary velocity of the driver is 600 revs/min, what would the
rotary velocity of the driven sprocket be?
Rotary Velocity of Driven Sprocket = Rotary Velocity of Driver Sprocket
Velocity Ratio
⇒ Rotary Velocity of driven = 600 = 600 x 3 = 900 revs/min
2
2
3
GEARS
Gears are toothed wheels which mesh
together and like pulleys and chain and
sprocket mechanisms can transmit rotary
motion and torque from one shaft to
another. The pair of gears opposite are
referred to as Spur Gears. The smaller
gear is called the pinion and the larger
gear the wheel. They form a Simple Gear
Train. The shafts rotate in opposite
directions and at different speeds since
the gears are different sizes.
If the driver gear has 15 teeth and the
driven 45 teeth calculate the Velocity
Ratio.
Driver
Driven
Driver
15 teeth
V.R. = No. of teeth on driven gear = 45
No. of teeth on driver gear
15
Driven
45 teeth
= 3/1 or 3:1
This means that 3 revolutions of the driver are required to make 1
revolution of the driven and that the driver rotates 3 times faster than
the driven.
To get the driver and driven gear to
rotate in the same direction an Idler
Gear is introduced between both driven
and driver. This changes the direction
of the driven gear. It does not affect
the Velocity Ratio of the gear train and
is ignored in Velocity Ratio calculations
IDLER
Page 10
COMPOUND
GEAR
TRAINS
To achieve greater velocity ratios
with gears a Compound Gear train
may be used. This involves meshing
2 or more pairs of gears as shown
opposite. The two middle gears in
the illustration are fused together
and rotate at the same speed. To
calculate the total velocity ratio we
obtain the product of the velocity
ratios for each pair of gears. In the
graphic symbol illustration of a
compound gear train A has 10 teeth,
B has 25 teeth, C has 10 teeth and
D has 20.
V.R. = 25 x 20
10 x 10
=
WORM
GEARS
Driver
Driver
5
1
In other words A rotates 5 times
faster than D.
Driven
Driven
Compound Gear Train
C
A
Driver
To achieve a large velocity ratio with
just one pair of gears a worm and
wormwheel may be used. The worm
has a helical groove cut into it like a
screw thread and the worm wheel is
similar to a spur gear. One revolution
of the worm causes one tooth of the
wormwheel to be moved. Hence the
Worm can be treated as a gear with
one tooth.
V.R. = No. of teeth on wormwheel
1
If the wormwheel has 60 teeth then
the Velocity ratio will be 60/1
D
B
Worm
Worm & Wormwheel
Unlike a simple gear train the shafts of the
worm and wormwheel are at 90° to each other.
This may or may not be an advantage. These
gears are widely used in industry as they are
very compact and give such large velocity
ratios. They also have the advantage that the
worm cannot be turned by the wormwheel.
This makes them very suitable as the drive
mechanism of a lifting system. One such crank
operated lifting device is shown opposite.
Worm gear unit with
MM28 motor
Graphic
symbol
Page 11
BEVEL GEARS
As With worm gears bevel gears involve the
transmission of motion between shafts which are
at 90° to each other. By using bevel gears of
different sizes the driver and driven shafts will
rotate at different speeds.
TORQUE
Torque (the turning force in a shaft) is an important consideration in
rotary type mechanisms. Where a mechanism results in a reduction in
speed from the driver to the driven shaft, this speed reduction is
compensated for by an increase in torque. The compound gear train on
page 11 resulted in a velocity ratio of 5:1. This gave rise to a five fold
reduction in speed from the driver to the final driven shaft. Ignoring
losses of energy due to friction, noise etc. the torque in the final driven
shaft will be five times greater than that in the driver shaft. This is why
one puts a bicycle or car in a low gear when going up a hill.
RACK &
PINION
Rack and pinion gears involve changes
in motion from linear to rotary or the
other way round. A common use of a
rack and pinion is the drill feed
mechanism of a pillar drill .
Pinion
Graphic Symbol
RATCHET
& PAWL
Rack
Drill Feed
Mechanism
To lock a mechanism so that it does not slip when under load a mechanism
known as a ratchet and pawl may be used. As the ratchet rotates the
pawl, which is usually spring loaded clicks into the teeth of the ratchet
preventing it from rotating in the opposite direction. Winches, spanners,
screw drivers and fishing reels are examples of devices which use ratchet
and pawl mechanisms.
Pawl
Pawl
Ratchet
Manually operated winch
Page 12
PULLEY
LIFTING
SYSTEMS
The Illustration opposite shows a man raising
a bucket up a scaffolding using a rope and
single pulley. Ignoring friction in the
mechanism the effort force applied by the
man to the rope is equal to the load force
produced by the bucket. This system does
not produce a mechanical advantage and the
velocity ratio is one.
Mech. Advantage = load/effort
Velocity Ratio = Distance moved by effort
Distance moved by load
By using more than one pulley a mechanical
advantage can be obtained. Consider the
pulley arrangement shown here. The load
of 400N is split evenly between both
parts of the cable holding the lower
moving pulley wheel. Hence the force in
each part of the cable is 200N. The
tension force in the cable is the same at
every point and so the effort force (which
is the tension force) must be 200N. The
mechanical advantage is then 2:1.
Another way of looking at this is to
consider the Velocity Ratio. If the load
was raised through a height of 0.5m then
the effort would have to move through a
distance of 1m. This is because both
elements of the cable holding up the
moving pulley must shorten by 0.5m. The
velocity ratio is therefore 2:1
The system opposite uses 4 pulleys with
two movable pulleys. This time the load
force splits evenly between 4 parts of the
cable and so the tension in each part is
250N. Again the tension is the same
throughout the cable and so the effort
force is 250N. The mechanical advantage
and velocity ratio is therefore 4:1. In all
these systems we treat the pulleys and
cables as having no weight and we assume
that the cable does not stretch. Strictly
speaking these factors would have to be
taken into account when real systems are
being designed by engineers.
1m
Effort = 200N
0.5m
Load = 400N
Effort
250N
Load
1000N
Lifting system using 4 pulleys
Page 13
CAMS
Cams are shaped pieces of metal or plastic
which are part of or fixed to a shaft. A
follower presses against the cam as it
rotates causing the follower to follow the
profile of the cam.
Follower
Stroke
The diagram opposite shows the different
Fall
terminology associated with cams. This cam
is a pear shaped cam and it causes the
Rise
follower to move up and down (reciprocate)
continuously. The height through which it
Rotation
moves is referred to as the stroke. The rise
clockwise
and fall motion of the follower is the same
Dwell
due to the symmetry of the cam. For half of
Cam Terminology
the revolution of the cam the follower is in
the dwell position and does not move. Pear
shaped cams are often used to control the
valves in an engine.
Cam shapes
Different cam shapes produce different
follower movements. The shapes
opposite are pear, eccentric circular and
heart shape. Eccentric circular cams are
used in some fuel pumps and heart
shaped cams in bobbins for winding
threads and wools.
Cam follower shapes
Followers may be weighted or spring loaded to ensure that they follow
accurately the shape or profile of the cam.
Radial arm follower
CRANK
SLIDERS
Roller follower
Knife follower
Point follower
Crank slider mechanisms are used to
convert rotary motion into
reciprocating motion and vice versa.
Flat follower
Slider
Guide
Connecting Rod
Crank
A car engine is a very good example of a crank slider
mechanism. The diagram shows the crankshaft of a 4
cylinder engine. As the pistons move up and down the
crankshaft rotates. Hence reciprocating motion is being
converted into rotary motion.
Page 14
LEVERS - 1
Identify the class of lever for each of the following practical levers and label its
load, effort and fulcrum. (the first three are worked examples.)
Load
Fulcrum
Class 2 Lever
Load
Fulcrum
Fulcrum
Load
Effort
Class 1 Lever
(a) Arm
Effort
Effort
Class 3 Lever
(b) Nutcracker
(d) Claw Hammer
(c) Crow Bar
Page 15
EVERS - I
LEVERS – 2
(e) Foot Brake
(f) Scissors
(g) Spanner
(h) Spade
(i) Forged Tongs
(k) Wheelbarrow
(j) Weighing Scales
(l) Microswitch
Page 16
LEVERS - 3
Question 1.
(a) Calculate the Mechanical Advantage for the lever shown if a Load of 60
Newton’s can be raised using an Effort of just 16 Newton’s.
Answer:
(b) Calculate the Velocity Ratio between the two movements – if the Load moves
through 300mm and the Effort moves through 1200mm.
Answer:
(c) Calculate the Efficiency of the above lever.
Answer:
MA x 100%
Efficiency = --------VR
(d) Explain why levers in principle are never 100% Efficient?
__________________________________________________________
______________________________________________
Page 17
LEVERS – 4
Question 2.
Calculate the Force applied to the lever micro switch at ‘X’ in the sketch.
0.3N
Answer:
40mm
10mm
X
Question 3.
For the two levers shown below attempt the following:
(a)
State its Class of lever.
(b)
Find the size of the Effort given that the Load in each case is 36N.
(c)
What is the Mechanical Advantage for the lever?
(i)
3M
Answer:
E
Load
F
1M
(ii)
4M
E
Answer:
2M
F
L
Page 18
PULLEY SYSTEMS - 1
Question 1.
Fill in the missing blanks for the following two sentences:
(a)
Machine shaft
Driven
(a)
(b)
(b)
Driven
Motor
Motor
Driver
Driver
When the motor pulley has a large diameter and the machine shaft driven pulley has a
small diameter we have a speed __________.
When the motor pulley has a small diameter and the machine shaft driven pulley has a
large diameter we have a speed __________.
Question 2.
The arrangement of pulleys shown in the diagram is called a ‘stepped cone’ pulley system. What
are the advantages of this system? On which machine in the Technology workshop can it be
located?
Question 3.
Calculate the Velocity Ratio for the Pulley System?
Driven
ø 75
Answer:
Driver ø 15
Page 19
PULLEY SYSTEMS - 2
Question 4.
In the diagram shown, is a Hoover brush cylinder fitted with a 30mm diameter
pulley and is being driven by a 90mm diameter pulley.
(i)
(ii)
Driven
Calculate the Velocity Ratio
Calculate the Cylinder speed when the
motor shaft is rotating at 1000rpm.
Motor
Driver
(ii) Answer:
(i) Answer:
Question 5.
Calculate for the Pulley systems the (i) Velocity Ratio & (ii) Mechanical advantage.
Effort 15N
1M
Load 30N
0.5M
1N - Effort
Answer:
4N - Load
Load
Page 20
CHAIN AND SPROCKET
Question 1.
Shown in the picture is a bicycle.
(a)
Name two working parts of the bicycle, which are levers?
(b)
State three advantages a chain and sprocket drive over a belt and pulley
drive in this application.
(c)
Identify four areas where friction is encountered in a bicycle, two of
which are of benefit to the cyclist and two of which are a disadvantage to
the cyclist. Suggest how the undesirable friction can be removed.
(d)
On the bicycle above, the driver sprocket (pedal) has 36 Teeth and the
driven sprocket (back wheel) has 12 Teeth, calculate:
(i) The Velocity Ratio.
12T
Answer:
36T
(ii)
Determine the road speed of the bicycle in metres/second (m/s) if
the pedal sprocket (Driver) rotates at 15 revs/minute? The
circumference of the wheel is 2.4 Metres in length.
Answer:
Page 21
GEAR SYSTEMS - 1
Question 1.
The illustrations show simple gear trains in mesh.
State:
(i)
A train that will not rotate,
(ii)
A train that gives no change in direction,
(iii) A train that gives no increase in speed,
(iv) A train that decreases speed,
(v)
A train that does not alter speed.
Answers:
(i)
(ii)
(iii)
(iv)
(v)
(The rotational arrow indicates the driver for each gear train).
Gear Train 1
Gear Train 2
Gear Train 3
Gear Train 4
Question 2.
Name the mechanisms below. Identify their main features? Name two practical
applications of each: one used in industry, the other from everyday life.
(a)
(b)
(c)
Page 22
GEAR SYSTEMS - 2
Question 3.
Drum
32 Teeth
Calculate the number of turns
Of the handle are required to
Rotate the drum three times.
Answer:
8 Teeth
Handle
Question 4.
18
12
Driven
Driver
A
A simple gear train is shown. (A symbolic
representation of the two gears in mesh is also
shown). Calculate the following:
(i)
The gear ratio?
(ii)
If the driver gear operates at 200 rpm
at what speed will the driven gear rotate?
Answer:
B
Question 5.
Shown is a compound gear train
Which has two pairs of meshed
Gears: A and B, and C and D.
A
B
Gear A has 30 Teeth
Gear B has 20 Teeth
Gear C has 40 Teeth
Gear D has 20 Teeth
The Driver Gear D rotates at 240rpm
(i)
(ii)
What is the gear ratio?
Calculate is the rotary
Speed of gear A?
C
D
Driver Gear - 240 rpm
Answer:
Page 23
GEAR SYSTEMS - 3
Question 6.
Identify the gear arrangements shown. Give a practical example of each. Fill in
your answers on the blank spaces provided:
(c)
(b)
(a)
(d)
(e)
Question 6.
A Rack has 200 teeth per metre,
which is meshed with a 20T Pinion gear.
If the pinion is rotated through one
revolution, how far will the rack go?
Answer:
Rack 200 Teeth
Per Metre
Pinion – 20 Teeth
Page 24
EXAMINATION QUESTIONS - 1
Question 1.
Driven – 54T
Answer:
(i)
If an additional 18 tooth gear
Wheel is placed between the
Driving and driven gears, what
Effect will this have on:
(i)
(ii)
The speed of the driven gear?
(ii)
Question 2.
The direction of the driven gear.
Identify clearly on the bicycle shown,
two areas where bearings are used.
Question 4.
Driving – 18 T
Question 3.
Name this Mechanism?
Answer:
___________________________
In the pulley system shown it was found that an
effort of 50N moving 2 Metres could lift a load of
80N through a distance of 1 Metre.
Using the formula shown calculate the efficiency of
the system.
Efficiency = Work got out ÷ Work put in.
50N
Answer:
80N
Question 5.
Name a mechanism, which will achieve
The direction change shown.
Mechanism
Answer: ______________________
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EXAMINATION QUESTIONS - 2
Question 6.
The sketches below show mechanisms that may be used for lifting loads.
40T
40T
20T
10T
X
Mechanism B
Y
Z
LOAD
(i)
40T
Mechanism A
10T
LOAD
40T
If the axle ‘X’ in Mechanism ‘A’ rotates at 50rpm, calculate the speed of the
motor.
The speed of this motor, stated in a component catalogue, is 800rpm.
Explain the difference between the catalogue speed and the calculated motor
speeds.
(ii)
Name the gear arrangement ‘Y’ in mechanism ‘B’.
Calculated the speed of axle ‘Z’, if the motor in Mechanism ‘B’ turns at 3200rpm.
(iii)
State two advantages of mechanism ‘B’ over mechanism ‘A’.
Answers:
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