electromagnetic brakes

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ELECTROMAGNETIC BRAKES ELECTROMAGNETIC BRAKES TEAM TEAM MEMBERS:- MEMBERS:- FACULTY ADVISOR- FACULTY ADVISOR- Sachin (07109048) Sachin (07109048) Mr. Dinesh Shukla Mr. Dinesh Shukla

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An electromagnet is a type of magnet whose magnetic field is produced by the flow of electric current. The magnetic field disappears when the current ceases. To concentrate the magnetic field, in an electromagnet the wire is wound into a coil, with many turns of wire lying side by side. The magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there .Strength of magnetic field depend on current through coil and magnetic permeability of the core material.

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Page 1: Electromagnetic Brakes

ELECTROMAGNETIC BRAKESELECTROMAGNETIC BRAKES

TEAM MEMBERS:-TEAM MEMBERS:-

FACULTY ADVISOR- Sachin (07109048)FACULTY ADVISOR- Sachin (07109048)Mr. Dinesh Shukla Faruque(07109056)Mr. Dinesh Shukla Faruque(07109056) Rakesh(07109044)Rakesh(07109044)

Page 2: Electromagnetic Brakes

CONTENTSCONTENTS

Limitations of conventional friction brakesLimitations of conventional friction brakes Introduction to Electromagnet & EM brakesIntroduction to Electromagnet & EM brakes Existing electro-mechanical brakesExisting electro-mechanical brakes ObjectiveObjective Design rig for electromagnetic braking systemDesign rig for electromagnetic braking system Material property and selectionMaterial property and selection Force generated in rotating discForce generated in rotating disc Relevant calculation regarding magnetic field and forceRelevant calculation regarding magnetic field and force Variation of engagement time with currentVariation of engagement time with current Advantages of electromagnetic brakesAdvantages of electromagnetic brakes Concept of integrated braking systemConcept of integrated braking system Eddy-current brake conceptEddy-current brake concept

Page 3: Electromagnetic Brakes

LIMITATIONS OF CONVENTIONAL FRICTION LIMITATIONS OF CONVENTIONAL FRICTION BRAKESBRAKES

• Friction between contact surfaces leads to generation of heat that Friction between contact surfaces leads to generation of heat that

causes temperature rise of components.causes temperature rise of components.• Rise in temperature cause decrease in friction co-efficient which Rise in temperature cause decrease in friction co-efficient which

adversely affect the torqueadversely affect the torque• Wear and tear of friction lining during braking.Wear and tear of friction lining during braking.• Performance reduction with passage of time ,so require more Performance reduction with passage of time ,so require more

maintenance.maintenance.•Take large space and have greater weight.Take large space and have greater weight.• It becomes self locking if properly not It becomes self locking if properly not

designed, in which frictional force is designed, in which frictional force is

strong enough to apply the brake without strong enough to apply the brake without

any external force.any external force.

Page 4: Electromagnetic Brakes

INTRODUCTION TO ELECTROMAGNET AND INTRODUCTION TO ELECTROMAGNET AND EM BRAKESEM BRAKES

An electromagnet is a type of magnet whose magnetic field is produced by An electromagnet is a type of magnet whose magnetic field is produced by the flow of electric current. The magnetic field disappears when the the flow of electric current. The magnetic field disappears when the current ceases. To concentrate the magnetic field, in an electromagnet the current ceases. To concentrate the magnetic field, in an electromagnet the wire is wound into a coil, with many turns of wire lying side by side. The wire is wound into a coil, with many turns of wire lying side by side. The magnetic field of all the turns of wire passes through the center of the coil, magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there .Strength of magnetic field depend creating a strong magnetic field there .Strength of magnetic field depend on current through coil and magnetic permeability of the core material.on current through coil and magnetic permeability of the core material.

EM brake works when core of the coil is magnetized .The magnetized core EM brake works when core of the coil is magnetized .The magnetized core tries to pull the disc and that attraction force slows down the rotating disc.tries to pull the disc and that attraction force slows down the rotating disc.

As some EM brake work with friction ,which make the disc stop very As some EM brake work with friction ,which make the disc stop very quickly in 1-3 sec , this kind of EM brake is called Electro-mechanical quickly in 1-3 sec , this kind of EM brake is called Electro-mechanical brake. But when friction part is removed it takes slight more time to stop brake. But when friction part is removed it takes slight more time to stop the disc .the disc .

Page 5: Electromagnetic Brakes

EXISTING ELECTRO-MECHANICAL BRAKESEXISTING ELECTRO-MECHANICAL BRAKES Power off brakes Power off brakes stop or hold a load when electrical power is stop or hold a load when electrical power is

either accidentally lost or intentionally disconnected. either accidentally lost or intentionally disconnected. A permanent magnet holding brake looks very similar to a A permanent magnet holding brake looks very similar to a standard power applied electromagnetic brake. It uses standard power applied electromagnetic brake. It uses permanent magnets to attract a single face armature. When the permanent magnets to attract a single face armature. When the brake is engaged, the permanent magnets create magnetic lines brake is engaged, the permanent magnets create magnetic lines of flux, which can turn attract the armature to the brake housing. of flux, which can turn attract the armature to the brake housing. To disengage the brake, power is applied to the coil which sets To disengage the brake, power is applied to the coil which sets up an alternate magnetic field that cancels out the magnetic flux up an alternate magnetic field that cancels out the magnetic flux of the permanent magnets .Typical applications include robotics, of the permanent magnets .Typical applications include robotics, holding brakes for Z axis ball screws and servo motor brakes.holding brakes for Z axis ball screws and servo motor brakes.

Electromagnetic Particle BrakeElectromagnetic Particle Brake - Magnetic particles (very - Magnetic particles (very similar to iron filings) are located in the powder cavity. When similar to iron filings) are located in the powder cavity. When electricity is applied to the coil, the resulting magnetic flux tries electricity is applied to the coil, the resulting magnetic flux tries to bind the particles together. The brake rotor passes through to bind the particles together. The brake rotor passes through these bound particles. As the particles start to bind together, a these bound particles. As the particles start to bind together, a resistant force is created on the rotor, slowing, and eventually resistant force is created on the rotor, slowing, and eventually stopping the output shaft.stopping the output shaft.

Page 6: Electromagnetic Brakes

Electromagnetic Hysteresis Power Brake When electricity is applied to the field, it creates an internal magnetic flux. That flux is then transferred into a hysteresis disk passing through the field. The hysteresis disk is attached to the brake shaft. A magnetic drag on the hysteresis disk allows for a constant drag, or eventual stoppage of the output shaft. Since these units can be controlled remotely, they are ideal for test stand applications where varying torque is required.

Multiple Disk Brakes When electricity is applied to the coil of an electromagnet, the magnetic flux attracts the armature to the face of the brake. As it does so, it squeezes the inner and outer friction disks together. The hub is normally mounted on the shaft that is rotating. The brake housing is mounted solidly to the machine frame. As the disks are squeezed, torque is transmitted from the hub into the machine frame, stopping and holding the shaft

Page 7: Electromagnetic Brakes

OBJECTIVEOBJECTIVE

Due to the problems faced by conventional friction brakes , we intend to Due to the problems faced by conventional friction brakes , we intend to design Electromagnetic Brakes which work by applying the magnetic force on design Electromagnetic Brakes which work by applying the magnetic force on a disc mounted on a shaft. Brake is applied when disc stops rotating due the a disc mounted on a shaft. Brake is applied when disc stops rotating due the resisting magnetic force exerted by the magnetic field of electromagnets and resisting magnetic force exerted by the magnetic field of electromagnets and hence the shaft stops rotating .hence the shaft stops rotating .

Page 8: Electromagnetic Brakes

METHODOLOGY-ELECTROMAGNETIC BRAKE SYSTEMMETHODOLOGY-ELECTROMAGNETIC BRAKE SYSTEM

How does a magnetic brake system work?How does a magnetic brake system work? Magnetic resistance works by passing a spinning metallic disk through a Magnetic resistance works by passing a spinning metallic disk through a

magnetic field. The magnetic field provides resistance to the spinning disk thus magnetic field. The magnetic field provides resistance to the spinning disk thus slowing it’s rotation. The amount of resistance can be increased or decreased by slowing it’s rotation. The amount of resistance can be increased or decreased by varying the strength of the magnetic field. Field strength is controlled by changing varying the strength of the magnetic field. Field strength is controlled by changing either the power of the magnet or the distance between the magnet and the either the power of the magnet or the distance between the magnet and the spinning disk.spinning disk.

Resistance Formula: Resistance is determined by three factors:Resistance Formula: Resistance is determined by three factors: Disk rpm, magnet power and the distance between the magnet and disk. The Disk rpm, magnet power and the distance between the magnet and disk. The

three factors are expressed as a ratio of one to one to one squared:three factors are expressed as a ratio of one to one to one squared:

RPM : MAGNET POWER : DISTANCE² = RESISTANCERPM : MAGNET POWER : DISTANCE² = RESISTANCE

The distance value is the most important part of the formula because it’s value is The distance value is the most important part of the formula because it’s value is squared. This means that very small changes in DISTANCE make very large squared. This means that very small changes in DISTANCE make very large changes in the resistance level.changes in the resistance level.

Page 9: Electromagnetic Brakes

METHODOLOGY CONTD..METHODOLOGY CONTD.. Because distance is such Because distance is such

an important part of the an important part of the resistance formula small resistance formula small variations can make large variations can make large differences in the amount differences in the amount of resistance. of resistance.

By placing magnets on By placing magnets on the sides the sides of of the disk the the disk the patented M‐Force patented M‐Force magnetic brake system magnetic brake system maintains a consistent maintains a consistent distance between the disk distance between the disk and magnets at all times. and magnets at all times. Maintaining a consistent Maintaining a consistent distance allows for fine distance allows for fine adjustment of the adjustment of the resistance level simply by resistance level simply by adjusting the magnetic adjusting the magnetic field power. This results field power. This results in a smooth resistance in a smooth resistance curve. curve.

A consistent distance betweenmagnet and disk produces asmoother resistance curve

farfrom disk

closeto disk

highresistance

lowresistance

variable distanceconsistent distance

other systems:distance between magnetand disk varies

m force:‐maintains a consistentdistance

Page 10: Electromagnetic Brakes

NECESSARY CALCULATIONSNECESSARY CALCULATIONS

Magnetic flux is found by the relationMagnetic flux is found by the relation

B = µNI / LB = µNI / L

wherewhere

µ is magnetic permeability of the core µ is magnetic permeability of the core

N is the number of turnsN is the number of turns

I is the current passing through the coilI is the current passing through the coil

L is the length of core(on which coil is wound)L is the length of core(on which coil is wound) Force is calculated by the relationForce is calculated by the relation

F=B²A/2µF=B²A/2µ

Page 11: Electromagnetic Brakes

EXPERIMENTAL SET UP AND METHODOLOGY USEDEXPERIMENTAL SET UP AND METHODOLOGY USED

Fig:- TEST MODEL

Page 12: Electromagnetic Brakes

AC motor characteristics

PARAMETERS VALUE Nominal armature voltage 220 V Nominal armature current 6 A Armature resistance 285 OhmMaximum speed 2800 rpmNominal shaft power 18 wMaximum torque 0.0614 N.m Torque constant 0.0102N.m/A

TEST DESIGN BED COMPONENTS

Page 13: Electromagnetic Brakes

TEST ELECTROMAGNETIC BRAKE CHARACTERISTICS

PARAMETER SYMBOL VALUE

electromagnet residual flux B 10.4 T

Number of turns of coil n 1900

Resistivity of disc material ρ 1.18x10e(-6) Ohm-m.

Number of electromagnet used p 4

Arc between north and south pole t 80 degree

Airgap width g 2.5 mm

Disc thickness e 3.5 mm

Disc inner radius R inner 5.5 cm

Disc outer radius R outer 9 cm

Page 14: Electromagnetic Brakes

Material Ult. Tensile strength

Yield Strength

Poisson’s Ratio

Shear strength

Electrical Resistivity

1018 Mild (low-carbon)

steel

63.8kpsi 53.7kpsi 0.303 2.15 kpsi 1.18x10e-6 ohm-m

6061- T6 Aluminum

45.0 kpsi 40.0 kpsi 0.330 3.77 kpsi 0.00000157 ohm-m

ASTM A36 Mild (low-

carbon) steel

58-79kpsi 36.3 kpsi 0.300 2.3 kpsi 7.2x10e6ohm-m

Page 15: Electromagnetic Brakes

MATERIALS EVALUATIONMATERIALS EVALUATION

Disc Disc an extremely strong material that can withstand the stresses produced by an extremely strong material that can withstand the stresses produced by

the high rate of rotation.the high rate of rotation. must be made of a slightly conductive material in order to efficiently host must be made of a slightly conductive material in order to efficiently host

eddy currents with the least amount of resistance possible ;eddy currents with the least amount of resistance possible ; should have good magnetic properties. should have good magnetic properties.

Mild steel (0.1 % C) is chosen as disc material having the following Mild steel (0.1 % C) is chosen as disc material having the following properties:properties:

ResistivityResistivity 10e-8Ohm m 10e-8Ohm m Shear strength=2.1 kpsiShear strength=2.1 kpsi

Disc OrientationDisc Orientation The disc will have only one orientation. It will mount perpendicularly to the The disc will have only one orientation. It will mount perpendicularly to the

drive shaft and the electromagnets while mounted in the middle of the paired drive shaft and the electromagnets while mounted in the middle of the paired coilscoils

Page 16: Electromagnetic Brakes

ELECTROMAGNET DESIGNELECTROMAGNET DESIGN

The construction is having four in numberThe construction is having four in number

a change of polarity in electromagnets applied to electromagnetic brakes will produce a change of polarity in electromagnets applied to electromagnetic brakes will produce

a higher force than only one direction of polaritya higher force than only one direction of polarity. . standard coated aluminum wire coiled around a ferrous metal core. Coating the standard coated aluminum wire coiled around a ferrous metal core. Coating the

aluminum wire will prevent corrosion and increase the life of the electromagnets and aluminum wire will prevent corrosion and increase the life of the electromagnets and maintain the efficiency of the overall braking system.maintain the efficiency of the overall braking system.

The number of turns of coated aluminum around our ferrous material will determine The number of turns of coated aluminum around our ferrous material will determine the strength of the induced magnetic field. the strength of the induced magnetic field.

a ferrous material, such as mild steel or iron, ideal for a metal core for a ferrous material, such as mild steel or iron, ideal for a metal core for electromagnets. Mild steel is chosen for our core material.electromagnets. Mild steel is chosen for our core material.

The electromagnet is mounted in pairs in series connection one after another.The electromagnet is mounted in pairs in series connection one after another.

Page 17: Electromagnetic Brakes

Core material mild steel

Number of turns of coil 1900Relative Permeability 800

Gauge diameter 28 swg

Area on the disc 45x32 mm2

Magnetic strength 10.6 T

Wire material standard coated aluminum wire

SPECIFICATIONS OF ELECTROMAGNET

Page 18: Electromagnetic Brakes

OTHERS COMPONENTS OTHERS COMPONENTS

1.A variable 0–220 V ac power source for the motor; 1.A variable 0–220 V ac power source for the motor;

2. A variable 0–6 A dc power source for the coil; 2. A variable 0–6 A dc power source for the coil;

3. Ammeters and voltmeters; 3. Ammeters and voltmeters;

4. Digital tachometer to accurately measure the angular speed of the motor;4. Digital tachometer to accurately measure the angular speed of the motor;

5. Electronic stopwatch;5. Electronic stopwatch;

6. Wooden base for support structure;6. Wooden base for support structure;

7. Regulators for regulating current supply in electromagnet.7. Regulators for regulating current supply in electromagnet.

8. Rectifier for converting dc into ac for electromagnet.8. Rectifier for converting dc into ac for electromagnet.

Page 19: Electromagnetic Brakes

STRESS DUE TO THE ROTATING DISC STRESS DUE TO THE ROTATING DISC

Where a = inner radiusWhere a = inner radius

b = outer radiusb = outer radius

v = Poisson’s ratiov = Poisson’s ratio

ρρ = material density = material density

ωω = angular velocity = angular velocity [rad/s][rad/s]

r = radius of interestr = radius of interest

The high rotation rate of the disc will The high rotation rate of the disc will cause enormous stresses within the disc. cause enormous stresses within the disc. The rotation is by far the source The rotation is by far the source contributing the largest amount of stress in contributing the largest amount of stress in the disc. the disc.

stresses act in both the tangential and stresses act in both the tangential and radial directions where tangential is radial directions where tangential is defined as the direction tangent to the defined as the direction tangent to the outer edge of the circle created by the outer edge of the circle created by the silhouette of the disc, and radial is defined silhouette of the disc, and radial is defined as the direction starting at the axis of as the direction starting at the axis of rotation of the disc and moving outward rotation of the disc and moving outward through the plane of the disc.through the plane of the disc.

Tangential stress = 0.343 N/mm²Tangential stress = 0.343 N/mm² Radial stress = 3.065 N/mm²Radial stress = 3.065 N/mm²

Page 20: Electromagnetic Brakes

STRESS DUE TO EDDY CURRENTSSTRESS DUE TO EDDY CURRENTS

If there is generation of eddy current If there is generation of eddy current then the forces that the eddy currents then the forces that the eddy currents cause on the disc oppose the direction cause on the disc oppose the direction of motion the disc. in the image below of motion the disc. in the image below the red arrows indicate the direction of the red arrows indicate the direction of rotation of the disc and the E vectors rotation of the disc and the E vectors represent the corresponding eddy-represent the corresponding eddy-current-forces on the differential ring current-forces on the differential ring element of the disc.element of the disc.

Page 21: Electromagnetic Brakes

EXPERIMENTAL RESULTS AND DISCUSSIONEXPERIMENTAL RESULTS AND DISCUSSION

Current verses magnetic field intensityCurrent verses magnetic field intensity

Sl.NoSl.No. . Current (mA) Magnetic field intensity (B) Current (mA) Magnetic field intensity (B) in telsa in telsa

01 01 90.5 2.59 90.5 2.59 02 130.5 3.74 02 130.5 3.74 03 172 4.93 03 172 4.93 04 210 04 210 6.01 05 250 6.01 05 250 7.16 06 7.16 06 270 7.73 07 270 7.73 07 320 9.172 320 9.172 08 370 08 370 10.60 10.60

Page 22: Electromagnetic Brakes

Fig ; Graph between current and magnetic field intensity

Page 23: Electromagnetic Brakes

BRAKING TIME OF THE DISCBRAKING TIME OF THE DISC

(i) (i) Current= 90.5 mA Current= 90.5 mA Voltage (v) rpm Braking time (sVoltage (v) rpm Braking time (s) ) 126.7 2250 2.3 126.7 2250 2.3

144.1 2450 2.8 144.1 2450 2.8 162.5 2600 3.15 162.5 2600 3.15

(ii) (ii) Current= 130 mA Current= 130 mA Voltage (v) rpm Braking time (Voltage (v) rpm Braking time (s) s)

126.7 2250 0.9 126.7 2250 0.9 144.1 2450 1.04 144.1 2450 1.04 162.5 2600 162.5 2600 1.131.13

(iii) (iii) Current=172 mA Current=172 mA Voltage (v) Rpm Braking time (sVoltage (v) Rpm Braking time (s) ) 126.7 2250 0.64 126.7 2250 0.64 144.1 2450 144.1 2450 0.88 162.5 2600 0.88 162.5 2600 0.98 0.98

Page 24: Electromagnetic Brakes

Fig: -Graph between braking time and current

Page 25: Electromagnetic Brakes

APPLICATIONSAPPLICATIONS

Electromagnetic brakeElectromagnetic brake Circular eddy current brake system is used in trailer cars Circular eddy current brake system is used in trailer cars Linear eddy current brake is used in railsLinear eddy current brake is used in rails In roller coasterIn roller coaster To create a torque on a driveshaft that connects a generator to a gearbox in an To create a torque on a driveshaft that connects a generator to a gearbox in an

aerospace application.aerospace application.

Our design modelOur design model

Various machines and equipments in gymnasiumVarious machines and equipments in gymnasium

Page 26: Electromagnetic Brakes

CONCLUSIONCONCLUSION

Despite its tremendous advantages in compactness and effectiveness, friction Despite its tremendous advantages in compactness and effectiveness, friction braking suffers from severe limitations:braking suffers from severe limitations:

- Loss of braking force with increasing temperature (fading phenomenon)- Loss of braking force with increasing temperature (fading phenomenon)- Warping of discs- Warping of discs- Wear of pads and rotors- Wear of pads and rotors- Complexity and fuel consumption of power assistance- Complexity and fuel consumption of power assistance- Slow response time due to power assistance, especially in trucks, buses and - Slow response time due to power assistance, especially in trucks, buses and

trainstrains- Complexity of controlling each wheel’s braking independently- Complexity of controlling each wheel’s braking independently- Necessity of complex and costly anti-lock controls- Necessity of complex and costly anti-lock controls- Risk of hydraulic fluid leak- Risk of hydraulic fluid leak- Risk of brake fluid contamination by water and subsequent loss of braking - Risk of brake fluid contamination by water and subsequent loss of braking

powerpower- Challenging integration with anti-lock, traction, and dynamic stability - Challenging integration with anti-lock, traction, and dynamic stability

controlscontrols

Page 27: Electromagnetic Brakes

CONCLUSION CONTD…CONCLUSION CONTD…

So the design brakes give us following advantages;So the design brakes give us following advantages;

-Reduced wear-Reduced wear

-Reduced sensitivity to fadingReduced sensitivity to fading

-Reduced fuel consumption of power assistanceReduced fuel consumption of power assistance

-Faster control dynamicsFaster control dynamics

-Easier integration with anti-lock, traction, and dynamic stability controlsEasier integration with anti-lock, traction, and dynamic stability controls

-Easy individual wheel braking controlEasy individual wheel braking control

-Electric actuation, no fluidElectric actuation, no fluid

Page 28: Electromagnetic Brakes

FUTURE SCOPEFUTURE SCOPE

Eddy Current Brake SystemEddy Current Brake System By changing the disc material(by using a non magnetic material , By changing the disc material(by using a non magnetic material ,

Aluminum),eddy current brake can be made.Aluminum),eddy current brake can be made. Eddy currents are produced due to relative motion between disc and Eddy currents are produced due to relative motion between disc and

perpendicular magnetic fieldperpendicular magnetic field These tend to slow down the disc due to opposing force produced by the eddy These tend to slow down the disc due to opposing force produced by the eddy

currents.currents.

Integrated BrakeIntegrated Brake It combines a friction brake with an eddy-current brake on the same caliperIt combines a friction brake with an eddy-current brake on the same caliper Reduced wear of friction padsReduced wear of friction pads Reduced sensitivity to wheel lockReduced sensitivity to wheel lock Faster control dynamicsFaster control dynamics

Page 29: Electromagnetic Brakes

REFERENCESREFERENCES

   [1] R. Limpert, Brake Design and Safety. Warrendale, PA: Society of Automotive Engineers, [1] R. Limpert, Brake Design and Safety. Warrendale, PA: Society of Automotive Engineers,

1999. 1999.    [2 ] Telma. (2004, December). Nos Produits. [Online]. Available: [2 ] Telma. (2004, December). Nos Produits. [Online]. Available: www.telma.com.. [3 ] H. Sakamoto, “Design of permanent magnet type compact ECB retarder,” Society of [3 ] H. Sakamoto, “Design of permanent magnet type compact ECB retarder,” Society of

Automotive Engineers #973228, pp. 19-25, 1997. Automotive Engineers #973228, pp. 19-25, 1997.    [4] J. Bigeon and J.C. Sabonnadiere, “Analysis of an electromagnetic brake,” IEEE Journal of [4] J. Bigeon and J.C. Sabonnadiere, “Analysis of an electromagnetic brake,” IEEE Journal of

Electric Machines and Power Systems, vol. 10, pp. 285-297, 1985.Electric Machines and Power Systems, vol. 10, pp. 285-297, 1985.  . [5] J.H. Wouterse, “Critical torque and speed of eddy current brake with widely separated soft . [5] J.H. Wouterse, “Critical torque and speed of eddy current brake with widely separated soft

iron poles,” in IEE Proceedings-B, vol. 138, no. 4, pp. 153-158, 1991.iron poles,” in IEE Proceedings-B, vol. 138, no. 4, pp. 153-158, 1991.    wikipedia: wikipedia: http://en.wikipedia.org/wiki/Eddy_current_brake    wikipedia: wikipedia: http://en.wikipedia.org/wiki/Electromagnetic_brake    Youtube : http://www.youtube.com/watch?v=TxYh6TodacM&feature=relatedYoutube : http://www.youtube.com/watch?v=TxYh6TodacM&feature=related

[9] A text book of machine design by R S KHURMI & J K GUPTA[9] A text book of machine design by R S KHURMI & J K GUPTA

Page 30: Electromagnetic Brakes

Thank U