Types of motion/movement

Teacher sheet

Mechanisms

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Linear motion Rotary motion Oscillating motion Reciprocating

Create motion

Change the type of motion

Change the speed of motion

Change the direction of motion

Pendulum clock – oscillating movement of the

pendulum produces rotary movement of the hands.

Bicycle – rotary movement of pedals transmits rotary

movement to wheels. (In this instance the

mechanisms also create a change in speed).

Sewing machine – rotary motion of the motor

produces reciprocating movement of the needle.

Electric drill – rotary movement of the motor transmits

rotary movement to the drill bit. (In this instance the

mechanisms also create a change in speed).

Well –- rotary movement of the handle produces

linear movement of the bucket.

Car engine – reciprocating movement of the piston

produces rotary movement of the crank shaft.

There are two types of motion, each with a variant. These can be described as follows:

Mechanisms can transmit motion of the same kind or can change it. The following are examples of everyday items which

demonstrate mechanisms of various kinds:

Mechanisms use power (energy) to:

Pupil Activity – Class discussionUsing the examples above think of some other examples to demonstrate different types of motion/movement.

movement in a straight linein one direction

circular movement inone direction

circular movement in twodirections in sequence,i.e. swinging backwards

and forwards

linear movement in twodirections in sequence;

i.e. moving backwards andforwards in a straight line

Teacher sheet

Mechanisms

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Rotary motion on The London Eye

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2

3

Pupil Exercise 11a) When the London Eye turns it is a perfect example of rotary (circular) motion. Can you think of any

other examples of rotary motion you may find on the London Eye?

1b) Think of everyday examples of objects that demonstrate rotary motion.

There are also several examples of mechanisms on the London Eye that include linear motion. For example:

The main drive wheels are mounted on mechanisms that allow pairs of wheels to be lifted off the rim and away to

the side.

Two electrical feeders are mounted on mechanisms that allow one to be connected to the rim power tracks whilst

the other is held free, as back-up.

The London Eye’s high wind locking devices incorporate linear motion mechanisms.

The London Eye displays many

examples of rotary motion, for example:

1. The wheel of the London Eye rotates

on its hub about the spindle

2. The capsules rotate through 360º in

one direction while the rim rotates a full

revolution in the other direction

3. The main drive generates the rotary

motion of the tyres which turn against

the rim and generate the rotary turning

of the London Eye

More information on each of these is

provided later in this section.

Teacher sheet

Mechanisms

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Components and devices

There are five main components and devices used in mechanisms. They are:

Gears

Toothed gears transmit rotary motionto rotary motion normally in theopposite direction. Movement canalso be reversed by making onegear a ring with internal teeth. Gearsare a ‘positive’ mechanism, i.e. theydo not slip.

Pulleys and beltsLevers

A rigid bar or rod whichpivots at a single pointalong its length.

Cams

A shaft with a ‘bump’ -creates oscillating orreciprocating movement insomething that touches it.

Cranks

A lever, link or shaft that isnot completely straight.

A brief description of other mechanisms, some of which can be found on the London Eye, is provided below:

Cables – pull only in a linear direction.

Pin joint – provide a pivotal point to allow rotary

movement in one plane.

Friction rollers – transmit rotary movement to

rotary movement. Movement can be reversed or

transmitted in the same direction. Like pulleys they

are not ‘positive’.

Pistons – provide reciprocating motion only.

Rotating shafts – transmit rotary to rotary

movement in the same direction.

Chains and toothed sprockets – transmit rotary

to rotary motion with change of speed in same

direction only. Like gears, these are a ‘positive’

mechanism.

Links – a rigid bar or rod which pivots at each end.

Guides – change direction of motion, can be

straight or curved.

Springs – flexible connections in a mechanism

system. They transmit forces, whilst allowing

components to move relative to each other.

Belts can be flat or grooved. Pulleystransmit rotary motion to rotary motionwith a change of speed in the samedirection only. They are not ‘positive’.They can be made positive by addingteeth to the belt and the pulley.

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Mechanisms

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Examining mechanisms on The London Eye

The structure itself is also a mechanism – a mechanism

that only moved once, when the wheel was lifted up.

This mechanism was built into the fundamental design of

the London Eye and can be identified by looking at the

three sets of cables that support the structure. Pin joints

at the bottom of the A-frame legs (where they sit on the

concrete pillars) provided the rotary movement that

allowed the A-frame legs to be pulled to a 65º position

with the aid of a special lifting crane. A second pin joint at

the top of the legs enabled a rotary movement of the hub

and spindle relative to the A-frame legs to bring the wheel

of the London Eye to its final upright position.

There are three main mechanisms demonstrated on the

London Eye:

The main drive wheels generate the rotary motion of

the Eye

Rotation cables ensure the hub rotates at the same

rate as the rim

The capsule’s drive mechanism applies rotary motion to

keep the capsule stable as the rim rotates

In addition, there are three secondary mechanisms:

The main drive wheel supports that can be retracted

for maintenance

The electrical power feeders that can be moved in

and out of service

The wheel locking mechanism for use in high winds

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Mechanisms

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Making The London Eye turnThe London Eye rotates about its hub in the same way

as a bicycle wheel but the energy to turn it is provided by

hydraulic motors, which in turn are driven by electric

pumps. This 'drive system' is situated in one of the

restraint towers. These are the two towers, one at each

end of the boarding platform.

The drive is applied to the rim using standard lorry tyres

which act as friction rollers. These are turned by hydraulic

motors. The rotary motion of the tyres/wheels generates

the rotary movement of the rim. One set of wheels rotates

in the same direction as the London Eye, the other in the

opposite direction.

This system is very quiet and allows the drive load to be

balanced across all the wheels. The system is made up

of four separate drive units, two on each side of the rim.

Four drive wheels in each unit grip the flat running beams

(rails) along each side of the rim's outer frame. The

positions of the wheels on the rim and the fact that the

running beam is made up of straight sections rather than

being a perfect circle mean that each wheel speed has

to be separately adjusted all the time for the main rim

speed to be constant. A computer controls each

hydraulic motor speed as necessary.Standard lorry tyres act as friction rollers by applying drive to the rim of the

London Eye.

There are two restraint towers, one at each end of the boarding platform.One of these houses the London Eye’s drive system.

The main drive wheels

Pupil activity – Class demonstrationDemonstrate how the rotary motion of the wheels turning against the rim makes the London Eye turn.

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Mechanisms

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Rotation cablesCable pull is applied to the outer edge of the hub causing the hub to move. These cables are arranged in two groups

of eight, one group on each side of the wheel so that the movement can be reversed. The principle is exactly as that

used on a bicycle, however on a bicycle the cables only go in one direction. If you look carefully at the wheel you can

see which group of rotation cables drives it in its normal direction and which group is used for reversing. The river side

rotation cables are the normal direction mechanisms, the land side ones are only used for reversing.

Rim restraint system

In addition to the drive system, there is also a horizontal

restraint system which uses vertical rollers to keep the rim

of the wheel running as close as possible to the boarding

platform, making it easy and safe for passengers to board.

This system maintains control over the gap between the

capsule and boarding platform that might otherwise vary

according to the wind speed at any one time.

Pupil Exercise 22a) The direction of motion of the moving tyres is marked on this diagram. (Shown on teacher sheet

page 5 in this section) Which way does the rim of the London Eye turn?

2b) This type of rotary motion is driven by friction. Can you explain how this works.

Studying the diagram will help your answer.

Gears transmit rotary motion. Spur gears have teeth cut or moulded into

their edges to mesh with other gears. Gears are either driver or driven

gears. If an electric motor has a small gear on its shaft this is the driver

gear, the one it meshes with is the driven gear.

If two gears mesh they normally turn in opposite directions. They can be

made to turn the same way by putting an idler gear between the two or by

creating a gear with teeth on an inside edge into which a spur gear can

mesh. Rack and pinion gears include a toothed strip (the rack) which

meshes with a gear wheel (the pinion).

Teacher sheet

Mechanisms

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Gears

Driver

Driven

Pinion

Rack

Pupil Exercise 3Study these pictures of gear trains. The number of teeth on the gears are indicated on the diagrams.

3a) What is the gear ratio for each gear train?

3b) How do the number of teeth on a gear affect its rotation? Record your answers to question 3a) in a table and try to

find a link between the number of teeth and the number of times the driver gear turns. Plot your findings on a graph.

Can you explain how this works. Studying the diagram will help your answer.

number of teeth on driven gear

number of teeth on driver gearGear ratio =

1. 2. 3. 4.

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Mechanisms

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Keeping the capsules stable

Pupil Exercise 4Using the downloadable templates, make a model of a rack and pinion gear from cardboard to

investigate how the capsules rotate.

The capsules are motorised for stability to ensure

maximum passenger comfort. Each capsule has its own

drive system below the floor which incorporates gears,

sprockets and chains within the mechanisms used to

turn the capsules and keep them level at all times.

Friction rollers were considered in the early stages, but

the capsules required a 'positive' drive to ensure that the

correct horizontal alignment is maintained.The capsules

are contained within circular mounting ringsfixed to the rim.

They rotate within these on bearings.

The inside of these rings is fitted with a circular toothed

rail. A motor beneath the floor drives a gear box which

changes the motor's speed of rotation through a train of

gears. A chain drive and pair of sprockets are used to

slow the motion further. These in turn are connected to

the gears of the capsule's drive mechanism which turn

against the toothed wheel. The gear and the toothed rail

are effectively a rack and pinion (albeit with the rack

being laid out in a large circle rather than flat).

The capsule turns 360º in one direction around this ring as

the rim completes a revolution in the other direction, keeping

the floor of the capsule level at all times during the flight.

If you have access to a mechanisms modelling kit, demonstrate the workings of a rack and pinion gear to

pupils before embarking on this activity.

Note for teachers

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Mechanisms

9

Hydraulics

Hydraulics uses compressed fluid to produce movement.

Compressors, cylinders, valves and tubes transfer the

fluid around a system and are capable of producing

linear or rotary motion. You will see hydraulics used on

bulldozers and diggers on building sites, lifting and

rotating their scoops.

The London Eye is fitted with 16 hydraulic motors, each

turning one of the wheels on the drive tower which

generate the movement of the rim. The hydraulic drive

system means that the London Eye starts and stops

smoothly because the hydraulic power can be used

either to drive the London Eye or to slow it to a stop.

The London Eye can be brought to a complete stop

within two metres in normal operations and an

emergency stop can be conducted in 0.5 metres with

absolute safety.

Each main drive wheel is on the end of a pivotted link: a

linear hydraulic plunger rotates the link to press the tyre

onto the rim.

Pairs of drive wheels can be lifted away from the rim for

maintenance or repairs by a system of pivotted links. A

linear hydraulic plunger creates the necessary movement.

The main electric supply to the rim can be moved on and

off the power tracks in a similar manner to the drive

wheels. There are two electrical feeder mechanisms, only

one is used at a time, the other being a back-up.

Hydraulically powered pins are also used for 'locking off' the rim in high winds. The London Eye is rotated to a

predetermined position where the locking pins are inserted through a hole in the rim steel. Hydraulic plungers are used to

lift the lock into position and another pushes the pin in. Lateral plungers then hydraulically press rubber rollers against the

side of the rim, to secure it even further.

A simple hydraulic system can be demonstrated by

using two syringes and a length of plastic tubing.

Fill one syringe with water and leave the second

one empty (making sure that the empty syringe is

plunged in fully). Now push the syringe full of water

and see what happens. The compressed fluid in

one syringe should push the other syringe out.

Class demonstration

Teacher sheet

Mechanisms

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Friction

What is friction?

When a construction the size and scale of the London Eye is in motion the engineers have to make sure that the parts move

as freely as possible. When flying the London Eye you will probably notice how quiet it is.

The designers specified that the ride must be as comfortable as possible for passengers, therefore every effort was made to

reduce friction.

Friction occurs when two surfaces rub against one another.

By reducing the amount of friction in the working of machinery the parts can move against each other more easily.

Consequently, they will not get as hot or wear down so quickly. One way to do this is to lubricate (or oil) the parts to make

them slippery.

Another way in which parts of machinery can be made to move more easily is with the use of bearings.

Pupil activity – Class demonstrationDemonstrate the effect of friction. Ask pupils to rub their hands together very quickly - they soon start to feel very warm.

Pupil activity – Homework activitySoap your hands and rub them together quickly - the friction levels are reduced.

Pupil activity – Class demonstrationPlace a pencil between your hands and see how easily they move when you rub them together.

The pencil acts like the rollers in a bearing.

Using two pieces of wood, demonstrate the friction when they are rubbed against one another.

Examine the difference when ball bearings are placed in a channel in one of the pieces of wood.

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Mechanisms

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Ensuring the smooth turning of The London EyeThe rim of the London Eye rotates on its hub around two

giant circular roller bearings which ensure its smooth

rotation. These bearings are made from case hardened

steel and are designed to have a lifespan of at least

200,000 hours.

The bearings help to transfer the 1200 tonne load of the

rim, cables and capsules to the spindle, by spreading the

weight evenly and reducing the friction to a very low level.

The bearings were purpose made. They use rollers held in

place by a cage rather than being allowed to run free. This

allows the rollers to be tightly spaced helping to spread

the loads more evenly.

By climbing inside the hub it is possible to inspect these

bearings. Grease samples are taken from the bearings to

ensure that they remain in good condition.

Pupil Exercise 55a) List three items that use bearings to help them turn smoothly?

5b) Choose one of these items and explain how bearings help them to move smoothly.

The bearings on the London Eye can be inspected by climbing inside the hub.

What is a bearing?The concept behind a bearing is that things roll better than

they slide. When things slide, the friction between surfaces

causes a force that slows things down. If however, two

surfaces can roll over each other, friction is reduced and

the object is allowed to move more freely.

Bearings do this by providing smooth metal balls or rollers

and a smooth inner and outer metal surface for the balls or

rollers to roll against. These balls or rollers 'bear' the load,

allowing the device to spin smoothly. Bearings are also

lubricated to help them roll smoothly.

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Mechanisms

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Smooth turning of the capsules

The circular rings around the capsules

are also bearings. Rollers between the

inner ring and the outer ring (that fixes

the capsule to the London Eye) ensure

the smooth turning of the capsules as

the gears in the capsule's drive system

turn against the toothed wheel.