1

Certificate Of Evaluation

College name: St.Joseph’s College of Engineering

Branch & Semester: Mechanical, VI Semester

S.NO Name of Students Register No. Title of Project Name of Guide

1. U.Gaspar 31710114035 Eddy Current Mr.K.M.B.Karthikeyan

2. G.Jeffy Shannon 31710114046 Braking

The report of the project works submitted by the above students in the partial

fulfillment for the award of the degree of Bachelor of Mechanical Engineering

of Anna University were evaluated and confirmed to be the reports of the work

done by the above students.

Submitted For University Viva Examination on _______________

Internal Examiner External Examiner

2

ACKNOWLEDGEMENT

We are personally indebted to so many people for the successful

completion of our project.

Our sincere thanks and profound sense of gratitude goes to our respected

Chairman Dr.Jeppiar M.A., B.L., Ph.D., for all his efforts and

administration in educating us in his institution. I take this opportunity to

thank our Managing Director Dr. Babu Manoharan M.A., M.B.A.,

Ph.D., for their kind co-operation in helping us complete this project.

We would like to express our gratitude to our Director Jaikumar

Christhurajan B.E., MBA, for his continued support towards our

project.

We would like to express our gratitude to our Principal Prof. Jolly

Abraham M.E., Ph.D., who has been a source of constant

encouragement and support.

We would like to express our gratitude to our Head of the Department

Dr. Vaddi Seshagiri Rao M.E., Ph.D., and the faculty of Mechanical

Engineering for their guidance and advice through our tenure. We

convey our sincere thanks to our internal guide Mr.K.M.B.Karthikeyan

M.E for his suggestions throughout the project duration.

3

CONTENTS

CHAPTER NO TOPIC PAGE NO

1 Abstract 4

2 What is Eddy Current 5

2.1 History of Eddy Current 6

2.2 Explanation of Eddy Current 7

2.3 Applications 11

3 Eddy Current Brake 14

4 Introduction to brakes 18

4.1 Characteristic of Brakes 20

4.2 Classification of brakes 22

5 Construction of Eddy current

brake

24

5.1 Calculations 25

5.2 Condition For Proper

Working

26

5.3 Component design and

orientation

31

6 Final looks of setup 34

7 Advantages & Disadvantages 35

8 Conclusion 36

4

1. ABSTRACT

When the magnetic flux associated with a magnetic material changes, a

current is produced that opposes the change producing it and is called

eddy current.

The setup consists of a metal drum which is fitted concentric with the

wheel hub and it rotates along with the wheel. An electromagnet is fitted

stationary around the rotating drum.

A variable current is applied to the electromagnet. The current charges

the electromagnet and magnetic flux is produced. As the drum rotates, the

flux associated with the drum changes. Hence the electric current opposes

the rotation of the wheel and hence braking is achieved.

5

2. EDDY CURRENTS

Eddy currents (also called Foucault currents) are currents induced in

conductors, opposing the change in flux that generated them. It is caused when

a conductor is exposed to a changing magnetic field due to relative motion of

the field source and conductor; or due to variations of the field with time. This

can cause a circulating flow of electrons, or a current, within the body of the

conductor. These circulating eddies of current create induced magnetic fields

that oppose the change of the original magnetic field due to Lenz's law, causing

repulsive or drag forces between the conductor and the magnet. The stronger the

applied magnetic field, or the greater the electrical conductivity of the

conductor, or the faster the field that the conductor is exposed to changes, then

the greater the currents that are developed and the greater the opposing field.

The term eddy current comes from analogous currents seen in water when

dragging an oar breadth wise: localized areas of turbulence known as eddies

give rise to persistent vortices.

Eddy currents, like all electric currents, generate heat as well as electromagnetic

forces. The heat can be harnessed for induction heating. The electromagnetic

forces can be used for levitation, creating movement, or to give a strong braking

effect. Eddy currents can also have undesirable effects, for instance power loss

in transformers. In this application, they are minimized with thin plates, by

lamination of conductors or other details of conductor shape.

Self-induced eddy currents are responsible for the skin effect in conductors. The

latter can be used for non-destructive testing of materials for geometry features,

6

like micro-cracks. A similar effect is the proximity effect, which is caused by

externally-induced eddy currents.

2.1 HISTORY

The first person to observe current eddies was François Arago (1786-1853), the

25th president of France, who was also a mathematician, physicist and

astronomer. In 1824 he observed what has been called rotator magnetism, and

the fact that most conductive bodies could be magnetized; these discoveries

were completed and explained by Michael Faraday (1791-1867).

In 1834, Heinrich Lenz stated Lenz's law, which says that the direction of

induced current flow in an object will be such that its magnetic field will oppose

the magnetic field that caused the current flow. Eddy currents develop

secondary flux that cancels a part of the external flux.

French physicist Leon Foucault (1819-1868) is credited with having discovered

Eddy currents. In September, 1855, he discovered that the force required for the

rotation of a copper disc becomes greater when it is made to rotate with its rim

7

between the poles of a magnet, the disc at the same time becoming heated by

the eddy current induced in the metal. The first use of eddy current for Non-

destructive testing occurred in 1879 when D. E. Hughes used the principles to

conduct metallurgical sorting tests.

2.2 EXPLANATION

As the circular plate moves down through a small region of constant magnetic

field directed into the page, eddy currents are induced in the plate. The direction

of those currents is given by Lenz's law, i.e. so that the plate's movement is

hindered.

When a conductor moves relative to the field generated by a source,

electromotive forces (EMFs) can be generated around loops within the

conductor. These EMFs acting on the resistivity of the material generate a

current around the loop, in accordance with Faraday's law of induction. These

currents dissipate energy, and create a magnetic field that tends to oppose the

changes in the field.

Eddy currents are created when a conductor experiences changes in the

magnetic field. If either the conductor is moving through a steady magnetic

field, or the magnetic field is changing around a stationary conductor, eddy

8

currents will occur in the conductor. Both effects are present when a conductor

moves through a varying magnetic field, as is the case at the top and bottom

edges of the magnetized region shown in the diagram. Eddy currents will be

generated wherever a conducting object experiences a change in the intensity or

direction of the magnetic field at any point within it, and not just at the

boundaries.

The swirling current set up in the conductor is due to electrons experiencing a

Lorentz force that is perpendicular to their motion. Hence, they veer to their

right, or left, depending on the direction of the applied field and whether the

strength of the field is increasing or declining. The resistivity of the conductor

acts to damp the amplitude of the eddy currents, as well as straighten their

paths. Lenz's law encapsulates the fact that the current swirls in such a way as to

create an induced magnetic field that opposes the phenomenon that created it. In

the case of a varying applied field, the induced field will always be in the

opposite direction to that applied. The same will be true when a varying external

field is increasing in strength. However, when a varying field is falling in

strength, the induced field will be in the same direction as that originally

applied, in order to oppose the decline.

An object or part of an object experiences steady field intensity and direction

where there is still relative motion of the field and the object (for example in the

center of the field in the diagram), or unsteady fields where the currents cannot

circulate due to the geometry of the conductor. In these situations charges

collect on or within the object and these charges then produce static electric

potentials that oppose any further current. Currents may be initially associated

with the creation of static potentials, but these may be transitory and small.

Eddy currents generate resistive losses that transform some forms of energy,

such as kinetic energy, into heat. This Joule heating reduces efficiency of iron-

9

core transformers and electric motors and other devices that use changing

magnetic fields. Eddy currents are minimized in these devices by selecting

magnetic core materials that have low electrical conductivity (e.g., ferrites) or

by using thin sheets of magnetic material, known as laminations. Electrons

cannot cross the insulating gap between the laminations and so are unable to

circulate on wide arcs. Charges gather at the lamination boundaries, in a process

analogous to the Hall Effect , producing electric fields that oppose any further

accumulation of charge and hence suppressing the eddy currents. The shorter

the distance between adjacent laminations (i.e., the greater the number of

laminations per unit area, perpendicular to the applied field), the greater the

suppression of eddy currents.

The conversion of input energy to heat is not always undesirable, however, as

there are some practical applications. One is in the brakes of some trains known

as eddy current brakes. During braking, the metal wheels are exposed to a

magnetic field from an electromagnet, generating eddy currents in the wheels.

The eddy currents meet resistance as charges flow through the metal, thus

dissipating energy as heat, and this acts to slow the wheels down. The faster the

wheels are spinning, the stronger the effect, meaning that as the train slows the

braking force is reduced, producing a smooth stopping motion. Induction

heating makes use of eddy currents to provide heating of metal objects.

2.2.1 Strength of eddy currents

Under certain assumptions (uniform material, uniform magnetic field, no skin

effect, etc.) the power lost due to eddy currents can be calculated from the

following equations:

For thin sheets:

10

For thin wires:

where: P - power dissipation (W/kg), Bp - peak flux density (T), d - thickness of

the sheet or diameter of the wire (m), f - frequency (Hz), ρ - resistivity (Ωm), D

- specific density (kg/m3).

It should be borne in mind that these equations are valid only under the so-

called "quasi-static" conditions, where the frequency of magnetisation does not

result in the skin effect, i.e. the electromagnetic wave fully penetrates the

material.

Therefore, the following things usually increase the size and effects of eddy

currents:

stronger magnetic fields - increases flux density B

faster changing fields (due to faster relative speeds or otherwise) -

increases the frequency f

thicker materials - increases the thickness d

Lower resistivity materials (aluminium, copper, silver etc.)

Some things reduce the effects:

weaker magnets - lower B

slower changing fields (slower relative speeds) - lower f

thinner materials - lower d

Slotted materials so that currents cannot circulate - reduced d or

coefficient in the denominator (6, 12, etc.)

laminated materials so that currents cannot circulate - reduced d

Higher resistance materials (silicon rich iron etc.)

11

2.2.2 Skin effect

In very fast changing fields due to skin effect the equations shown above are not

valid because the magnetic field does not penetrate the material uniformly.

However, in any case increased frequency of the same value of field will always

increase eddy currents, even with non-uniform field penetration.

2.3 APPLICATIONS

I. Repulsive effects and levitation

In a fast varying magnetic field the induced currents, in good conductors,

particularly copper and aluminium, exhibit diamagnetic-like repulsion effects

on the magnetic field, and hence on the magnet and can create repulsive effects

and even stable levitation, albeit with reasonably high power dissipation due to

the high currents this entails.

They can thus be used to induce a magnetic field in aluminum cans, which

allows them to be separated easily from other recyclables. With a very strong

handheld magnet, such as those made from neodymium, one can easily observe

a very similar effect by rapidly sweeping the magnet over a coin with only a

small separation. Depending on the strength of the magnet, identity of the coin,

and separation between the magnet and coin, one may induce the coin to be

pushed slightly ahead of the magnet - even if the coin contains no magnetic

elements, such as the US penny.

Perfect conductors allow lossless conduction that allows eddy currents to form

on the surface of the conductor that exactly cancel any changes in the magnetic

field applied to the object after the material's resistance went to zero, thus

allowing magnetic levitation. Superconductors are a subclass of perfect

12

conductors in that they also exhibit the Meissner Effect, an inherently quantum

mechanical phenomenon that is responsible for expelling any magnetic field

lines present during the superconducting transition, thus making the magnetic

field zero in the bulk of the superconductor.

II. Identification of metals

In coin operated vending machines, eddy currents are used to detect counterfeit

coins, or slugs. The coin rolls past a stationary magnet, and eddy currents slow

its speed. The strength of the eddy currents, and thus the retardation, depends on

the conductivity of the coin's metal. Slugs are slowed to a different degree than

genuine coins, and this is used to send them into the rejection slot.

III. Vibration | Position Sensing

Eddy currents are used in certain types of proximity sensors to observe the

vibration and position of rotating shafts within their bearings. This technology

was originally pioneered in the 1930s by researchers at General Electric using

vacuum tube circuitry. In the late 1950s, solid-state versions were developed by

Donald E. Bentley at Bentley Nevada Corporation. These sensors are extremely

sensitive to very small displacements making them well suited to observe the

minute vibrations (on the order of several thousandths of an inch) in modern

turbo machinery. A typical proximity sensor used for vibration monitoring has a

scale factor of 200 mV/mil. Widespread use of such sensors in turbo machinery

has led to development of industry standards that prescribe their use and

application. Examples of such standards are American Petroleum Institute (API)

Standard 670 and ISO 7919.

13

2.3.1 Electromagnetic braking

Braking forces resulting from eddy currents in a metal plate moving through an

external magnetic field

Eddy currents are used for braking at the end of some roller coasters. This

mechanism has no mechanical wear and produces a very precise braking force.

Typically, heavy copper plates extending from the car are moved between pairs

of very strong permanent magnets. Electrical resistance within the plates causes

a dragging effect analogous to friction, which dissipates the kinetic energy of

the car. The same technique is used in electromagnetic brakes in railroad cars

and to quickly stop the blades in power tools such as circular saws.

2.3.2 Structural testing

Eddy current techniques are commonly used for the nondestructive examination

(NDE) and condition monitoring of a large variety of metallic structures,

including heat exchanger tubes, aircraft fuselage, and aircraft structural

components..

2.3.3 Side effects

Eddy currents are the root cause of the skin effect in conductors carrying AC

current.

14

Similarly, in magnetic materials of finite conductivity eddy currents cause the

confinement of the majority of the magnetic fields to only a couple skin depths

of the surface of the material. This effect limits the flux linkage in inductors and

transformers having magnetic cores.

3. EDDY CURRENT BRAKE

An eddy current brake of a German ICE 3 in action.

An eddy current brake, like a conventional friction brake, is responsible for

slowing an object, such as a train or a roller coaster. Unlike friction brakes,

which apply pressure on two separate objects, eddy current brakes slow an

object by creating eddy currents through electromagnetic induction which create

resistance, and in turn either heat or electricity.

15

3.1.1 Construction and operation

i. Circular eddy current brake

Circular eddy current brake on 700 Series Shinkansen

Electromagnetic brakes are similar to electrical motors; non-ferromagnetic

metal discs (rotors) are connected to a rotating coil, and a magnetic field

between the rotor and the coil creates a resistance used to generate electricity or

heat. When electromagnets are used, control of the braking action is made

possible by varying the strength of the magnetic field. A braking force is

possible when electric current is passed through the electromagnets. The

movement of the metal through the magnetic field of the electromagnets creates

eddy currents in the discs. These eddy currents generate an opposing magnetic

field, which then resists the rotation of the discs, providing braking force. The

net result is to convert the motion of the rotors into heat in the rotors.

16

ii. Linear eddy current brake

The principle of the linear eddy current brake has been described by the French

physicist Foucault, hence in French the eddy current brake is called the "frein à

courants de Foucault".

The linear eddy current brake consists of a magnetic yoke with electrical coils

positioned along the rail, which are being magnetized alternating as south and

north magnetic poles. This magnet does not touch the rail, as with the magnetic

brake, but is held at a constant small distance from the rail (approximately seven

millimeters). It does not move along the rail, exerting only a vertical pull on the

rail.

When the magnet is moved along the rail, it generates a non-stationary magnetic

field in the head of the rail, which then generates electrical tension (Faraday's

induction law), and causes eddy currents. These disturb the magnetic field in

such a way that the magnetic force is diverted to the opposite of the direction of

the movement, thus creating a horizontal force component, which works against

the movement of the magnet.

The braking energy of the vehicle is converted in eddy current losses which lead

to a warming of the rail. (The regular magnetic brake, in wide use in railways,

exerts its braking force by friction with the rail, which also creates heat.)

The eddy current brake does not have any mechanical contact with the rail, and

thus no wear, and creates no noise or odor. The eddy current brake is unusable

at low speeds, but can be used at high speeds both for emergency braking and

for regular braking.

17

Eddy current brakes at the Intamin roller coaster Goliath in Walibi World

(Netherlands)

Modern roller coasters use this type of braking, but utilize permanent magnets

instead of electromagnets, and require no electricity. However, their braking

strength cannot be adjusted as easily as with an electromagnet.

18

4. INTRODUCTION TO BRAKES

A brake is a device which inhibits motion. Its opposite component is a clutch.

The rest of this article is dedicated to various types of vehicular brakes.

Most commonly brakes use friction to convert kinetic energy into heat, though

other methods of energy conversion may be employed. For example

regenerative braking converts much of the energy to electrical energy, which

may be stored for later use. Other methods convert kinetic energy into potential

energy in such stored forms as pressurized air or pressurized oil. Still other

braking methods even transform kinetic energy into different forms, for

example by transferring the energy to a rotating flywheel.

Brakes are generally applied to rotating axles or wheels, but may also take other

forms such as the surface of a moving fluid (flaps deployed into water or air).

Some vehicles use a combination of braking mechanisms, such as drag racing

cars with both wheel brakes and a parachute, or airplanes with both wheel

brakes and drag flaps raised into the air during landing.

Since kinetic energy increases quadratically with velocity (K = mv2 / 2), an

object traveling at 10 meters per second has 100 times as much energy as one

traveling at 1 meter per second, and consequently the theoretical braking

distance, when braking at the traction limit, is 100 times as long. In practice,

fast vehicles usually have significant air drag, and energy lost to air drag rises

quickly with speed.

Almost all wheeled vehicles have a brake of some sort. Even baggage carts and

shopping carts may have them for use on a moving ramp. Most fixed-wing

aircraft are fitted with wheel brakes on the undercarriage. Some aircraft also

feature air brakes designed to reduce their speed in flight. Notable examples

include gliders and some World War II-era aircraft, primarily some fighter

19

aircraft and many dive bombers of the era. These allow the aircraft to maintain a

safe speed in a steep descent. The Saab B 17 dive bomber used the deployed

undercarriage as an air brake.

Friction brakes on automobiles store braking heat in the drum brake or disc

brake while braking then conduct it to the air gradually. When traveling

downhill some vehicles can use their engines to brake.

When the brake pedal is pushed a piston pushes the pad towards the brake disc

which slows the wheel down. On the brake drum it is similar as the cylinder

pushes the brake shoes towards the drum which also slows the wheel down.

Brakes may be broadly described as using friction, pumping, or

electromagnetic. One brake may use several principles: for example, a pump

may pass fluid through an orifice to create friction.

Frictional brakes are most common and can be divided broadly into "shoe" or

"pad" brakes, using an explicit wear surface, and hydrodynamic brakes, such as

parachutes, which use friction in a working fluid and do not explicitly wear.

Typically the term "friction brake" is used to mean pad/shoe brakes and

excludes hydrodynamic brakes, even though hydrodynamic brakes use friction.

Friction (pad/shoe) brakes are often rotating devices with a stationary pad and a

rotating wear surface. Common configurations include shoes that contract to rub

on the outside of a rotating drum, such as a band brake; a rotating drum with

shoes that expand to rub the inside of a drum, commonly called a "drum brake",

although other drum configurations are possible; and pads that pinch a rotating

disc, commonly called a "disc brake". Other brake configurations are used, but

less often. For example, PCC trolley brakes include a flat shoe which is

clamped to the rail with an electromagnet; the Murphy brake pinches a rotating

drum, and the Ausco Lambert disc brake uses a hollow disc (two parallel discs

20

with a structural bridge) with shoes that sit between the disc surfaces and

expand laterally.

Pumping brakes are often used where a pump is already part of the machinery.

For example, an internal-combustion piston motor can have the fuel supply

stopped, and then internal pumping losses of the engine create some braking.

Some engines use a valve override called a Jake brake to greatly increase

pumping losses. Pumping brakes can dump energy as heat, or can be

regenerative brakes that recharge a pressure reservoir called an hydraulic

accumulator.

Electromagnetic brakes are likewise often used where an electric motor is

already part of the machinery. For example, many hybrid gasoline/electric

vehicles use the electric motor as a generator to charge electric batteries and

also as a regenerative brake. Some diesel/electric railroad locomotives use the

electric motors to generate electricity which is then sent to a resistor bank and

dumped as heat. Some vehicles, such as some transit buses, do not already have

an electric motor but use a secondary "retarder" brake that is effectively a

generator with an internal short-circuit.

4.1 CHARACTERISTICS

Brakes are often described according to several characteristics including:

Peak force The peak force is the maximum decelerating effect that can

be obtained. The peak force is often greater than the traction limit of the

tires, in which case the brake can cause a wheel skid.

Continuous power dissipation Brakes typically get hot in use, and fail

when the temperature gets too high. The greatest amount of power

(energy per unit time) that can be dissipated through the brake without

21

failure is the continuous power dissipation. Continuous power dissipation

often depends on e.g., the temperature and speed of ambient cooling air.

Fade As a brake heats, it may become less effective, called brake fade.

Some designs are inherently prone to fade, while other designs are

relatively immune. Further, use considerations, such as cooling, often

have a big effect on fade.

Smoothness A brake that is grabby, pulses, has chatter, or otherwise

exerts varying brake force may lead to skids. For example, railroad

wheels have little traction, and friction brakes without an anti-skid

mechanism often lead to skids, which increases maintenance costs and

leads to a "thump thump" feeling for riders inside.

Power Brakes are often described as "powerful" when a small human

application force leads to a braking force that is higher than typical for

other brakes in the same class. This notion of "powerful" does not relate

to continuous power dissipation, and may be confusing in that a brake

may be "powerful" and brake strongly with a gentle brake application, yet

have lower (worse) peak force than a less "powerful" brake.

Pedal Feel Brake pedal feel encompasses subjective perception of brake

power output as a function of pedal travel. Pedal travel is influenced by

the fluid displacement of the brake and other factors.

Drag Brakes have varied amount of drag in the off-brake condition

depending on design of the system to accommodate total system

compliance and deformation that exists under braking with ability to

retract friction material from the rubbing surface in the off-brake

condition.

Durability Friction brakes have wear surfaces that must be renewed

periodically. Wear surfaces include the brake shoes or pads, and also the

22

brake disc or drum. There may be tradeoffs, for example a wear surface

that generates high peak force may also wear quickly.

Weight Brakes are often "added weight" in that they serve no other

function. Further, brakes are often mounted on wheels, and unsprung

weight can significantly hurt traction in some circumstances. "Weight"

may mean the brake itself, or may include additional support structure.

Noise Brakes usually create some minor noise when applied, but often

create squeal or grinding noises that are quite loud.

4.2 CLASSIFICATION

1. According to the applications

i) Service or running or foot brake

ii) Parking or emergency or hand brake

23

2. According to the number of wheels

i) 2 wheel brakes

ii) 4 wheel brakes

3. According to the brake gear

i) Mechanical brake

a) Hand brake

b) Foot brake

ii) Power brake

a) Booster

b) Non-booster

4. According to the construction

i) Drum brake

ii) Disc brake

5. According to the location

i) Transmission brakes

ii) Wheel brakes

6. According to the method of braking contact

i) Internal expanding brakes

ii) External expanding brakes

7. According to the power unit

i) Cylinder brake

ii) Diaphragm brake

24

8. According to the power transmission

i) Direct acting brake

ii) Geared brake

9. According to the power employed

i) Vacuum brakes

ii) Air brakes

iii) Hydraulic brakes

iv) Hydrostatic brakes

v) Electric brakes

5. CONSTRUCTION OF EDDY CURRENT BRAKING

SYSTEM

Basically it begins with construction of the frame onto which houses

many parts like the motor (used to run the drum), metallic drum etc. The

metallic frame is properly welded using arc welding technique.

A motor capable of producing apt output power is fit onto the lower side

of the frame. The motor provides rotational motion to the metallic drum

depending upon its rating. The metallic drum acting as the wheel is fit

onto the top part of the frame.

An electromagnet is placed around the metallic drum. It is connected to

AC (optional) power source. When electric supply is given, the

electromagnet gets charged and produces magnetic flux which in turn

produces braking effect on the drum when it rotates.

25

CALCULATIONS

Coil windings: 7 turns per volt; 50 cycle per square

:> (7/2)=3.5*230v = 805 turns

Torque, T= pulley tension ×radius

Brake power, BP= 2ΠNT

Brake thermal efficiency, η= (BP/mf× cv)

Bending stress, σ = (Eᵣ×d/ D) = (0.84×10^5 ×10/200) = 4.2×10^3 N/mm²

Amount of wear, p= (2T/ d× D)

Arc of contact= 180˚- (200-60/ 450) ×60˚ = 161.3˚

Design Power = (Rated KW × load correction factor/ arc of contact

Factor × small pulley factor)

= (2 × 1.0/0.6×1.08) = 3.086 KW

26

5. CONDITIONS FOR PROPER WORKING

5.1 ENVIRONMENTAL CONDITIONS

a) TEMPERATURE

We were given a temperature constraint of the brake to operate

between -50 degrees Fahrenheit to 300 degrees Fahrenheit. This

constraint sets a design limitation that must take into consideration

the materials used for our design.

b) HUMIDITY

The brake has to function in an environment containing a range of

10% to 80% humidity. This will obviously limit out choice of

materials because we do not want the material to deteriorate due to

moisture. Other than material choice we don’t not believe this will

limit our design any more than material choice. The humidity may

even act as an aide in the cooling of a braking system.

27

c) BALANCE

Our design must be balanced to 0.005 oz. in. for all rotating parts.

This precedence was established so the rotating parts will not have an

effect on the operation of the generator. An imbalance will create an

additional stress in the rotating part as well. The effect an imbalance

will have on our design will be explained in the Final Design section

of this report.

d) OIL MIST

The Braking system will operate in an oil mist environment. This

will create a limitation for a couple of our design concepts, however

will create an advantage for one of the designs in the form of cooling

which will be discussed in the Final Design section of this Report.

e) ELEVATION

Our brake system design must function within an elevation range of

3000 feet below sea level to 70,000 feet above sea level. This will

simulate the broad application of the braking system as well as the

operable elevations of the generators. We cannot completely neglect

any effect the elevation will have and have considered the effect of

elevation with respect to our final design.

28

f) Pressure

The pressure range we have considered in our Final Design will work

within 0.75 to 1 atmosphere. The pressure range will also take into

account the elevation change as well as any differential pressure

between the pressure due to elevation and the pressure in which the

generator creates.

5.1.1 Operational Conditions

1) Angular Velocity

We must design a gracing system that will operate at a minimum

angular velocity of 400 rotations per minute and a maximum angular

velocity of 1600 rotations per minute. This constraint will have an

effect on each of the concepts in its own way and was a major factor

in determining a final design.

.

2) Power Source

Our design will operate with a limited power source of 230 volts DC.

This constraint operates with the power supply allowed by the

generator. On top of operation at this power input we must develop a

test rig that simulates the power supply.

29

5.1.2 Functional Conditions

a. Duty Cycle

Our braking mechanism should not deteriorate over time. We also

need it to last for the life of the generator. Due to the fact that this

activation system must act when triggered we cannot have any part

fail due to deterioration.

b. Design Envelop

Our Braking system design must fit into a design envelop of a 5 inch

Diameter and a 1.25 inch width. The free area of our disk will also

depend on the drive shaft diameter which will have an effect on one

of our proposed design concepts.

c. Hazardous Material

We may not have any hazardous material for unspecified reasons

stated. Fortunately for our Proposed Designs, we will not require the

use of any hazardous materials.

30

d. Reliability

Our final design and product must have a reliability of 99%

operational readiness. Our product must work when triggered. Late

activation or no activation may cause irreversible damage to the

gearbox, generator, or both. It has to work with NO uncertainty.

5.3 Component Orientation

a. Electromagnet Orientation

We will use a total of four pairs of electromagnets per request of

Honeywell. We will need to use four pairs or less in order to fall

under the weight limitation of our design. The pairs will be oriented

with the polarities aligning North to South and the brake spinning

between the pairs. We will build our own electromagnet coils using

materials defined in this report, later in this section. By building our

own electromagnets we may establish their polarity and when

orienting them in the housing we will alternate the directions of

polarity. Alternating the polarity will produce a greater force in our

final product. In addition to opposite polarity it may not make a

difference where we mount the electromagnets, so long as they are

mounted very close and perpendicular to the brake and not too close

to each other. We will optimize this property of our design with

31

further testing and analysis. A study done has proved that a change

of polarity in electromagnets applied to eddy current brakes will

produce a higher force than only one direction of polarity. We will

likely mount the magnets depicted, however upon testing we may

conclude that having the magnets closer together may create the

maximum torque. Further testing will either prove or disprove this

concept.

b. Drum Orientation

The brake will have only one orientation. It will mount

perpendicularly to the drive shaft and the electromagnets while

mounted in the middle of the paired coils. One major concern comes

in the form of how we will fasten the disk to the drive shaft. We will

most likely pressure fit a collar around the drive shaft thereby

attaching the brake by way of a pressure fit collar. If this is not

feasible, we will conduct further review and brainstorming for a new

way to fasten the brake to the drive shaft.

5.3 Component Design

5.3.1 Electromagnet Design

The electromagnets will be built and assembled by our team.

Building our own electromagnets gives us the ability to generate the

32

magnetic field needed. We will use standard coated copper wire

coiled around a ferrous metal core. Coating the copper wire will

prevent corrosion and increase the life of the electromagnets and

maintain the efficiency of the overall braking system. The number of

turns of copper around our ferrous material will determine the

strength of the induced magnetic field. Upon further analysis with the

Faraday computer program we will determine how many turns are

needed per coil as well as the amperage needed to provide the needed

magnetic field, which determines the force generated. Building our

own to the needed specifications will also cut down on cost of the

product as well as give specifications to build their own, have

outsourced, or purchase.

After researching electromagnet design we determined a ferrous

material, such as 409 stainless steel or iron, ideal for a metal core for

electromagnets. When constructing the electromagnet components,

we will coat the copper wires and exposed core with a protective

epoxy coating as to not leave the electromagnets exposed to the

environment established earlier in this report. When mounting the

electromagnets we will mount them in pairs. By pairing the

electromagnets and aligning north-south polarity we will direct and

concentrate the magnetic field to ensure a perpendicular magnetic

field with maximum possible magnitude. The magnetic pairs will

produce a similar magnetic field to the illustration in figure 3.

33

Figure : Magnetic field lines of Coil Pairs

5.3.2 Conducting Brake Design

The design of the brake is fairly simple. We will use a highly

conductive material that will also keep its shape and material

properties over the lifetime of the generator. If the brake becomes

warped, looses conductivity or fails in some other manner results in

the overall failure of the ECBS. Assuring the material used to

perform adequately is detrimental to the success of the ECBS’s

function as an activation system.

34

6. FINAL EDDY CURRENT BRAKE SETUP

35

7. ADVANTAGES

It uses electromagnetic force and not mechanical friction.

Non-mechanical (no moving parts, no friction) contact so less friction and

consequently less wear.

Fully resettable

Can be activated at will via electrical signal.

Low maintenance

Light weight

DISADVANTAGES

Braking force diminishes as speed diminishes with no ability to

hold the load in position at standstill.

It can be used only where the infrastructure has been developed

to accept them.

It is applicable only for low speed objects.

36

CONCLUSION

The ordinary brakes which are being used nowadays stop the

vehicle by means of mechanical blocking. This causes skidding

and wear and tear of the tire. If the speed of the vehicle is very

high, it cannot provide that much high braking force and it will

cause problems.

These drawbacks of ordinary brake can be overcome by

implying “eddy current braking” system.

It is an abrasion free method for braking of vehicles including

trains.