10802569_Term Paper Dc Motors

Term Paper On DC Motor :-

Name :- Sahil Mehta.

Roll No :- 35

Section :- 256

Reg No :- 10802569

Submitted To :-

Suman Rani

(Department Of Physics)

Contents :-

1) Intorduction

Intoduction About DC Motors

How Does DC Motor Works

2) Types

Brushed DC Motors.

Coreless DC Motors.

Coreless Or Ironless DC Motors.

3) Review Of DC Motor

Inside A DC Motor.

History And Background.

Articles By Scientist.

4) Sugesstion And Clussion .

5) References.

Introduction:

Industrial applications use dc motors because the speed-torque relationship can be varied to almost any useful form -- for both dc motor and regeneration applications in either direction of rotation. Continuous operation of dc motors is commonly available over a speed range of 8:1. Infinite range (smooth control down to zero speed) for short durations or reduced load is also common.

Dc motors are often applied where they momentarily deliver three or more times their rated torque. In emergency situations, dc motors can supply over five times rated torque without stalling (power supply permitting).

Dynamic braking (dc motor-generated energy is fed to a resistor grid) or regenerative braking (dc motor-generated energy is fed back into the dc motor supply) can be obtained with dc motors on applications requiring quick stops, thus eliminating the need for, or reducing the size of, a mechanical brake.

Dc motors feature a speed, which can be controlled smoothly down to zero, immediately followed by acceleration in the opposite direction -- without power circuit switching. And dc motors respond quickly to changes in control signals due to the dc motor's high ratio of torque

DC Motors

A DC motor is designed to run on DC electric power. Two examples of pure DC designs are Michael Faraday's homopolar motor (which is uncommon), and the ball bearing motor, which is (so far) a novelty. By far the most common DC motor types are the brushed and brushless types, which use internal and external commutation respectively to create an oscillating AC current from the DC source -- so they are not purely DC machines in a strict sense.

How Does DC Motor Works

Brushed DC electric motor

The classic DC motor design generates an oscillating current in a wound rotor with a split ring commutator, and either a wound or permanent magnet stator. A rotor consists of a coil wound around a rotor which is then powered by any type of battery.

Many of the limitations of the classic commutator DC motor are due to the need for brushes to press against the commutator. This creates friction. At higher speeds, brushes have increasing difficulty in maintaining contact. Brushes may bounce off the irregularities in the commutator surface, creating sparks. This limits the maximum speed of the machine. The current density per unit area of the brushes limits the output of the motor. The imperfect electric contact also causes electrical noise. Brushes eventually wear out and require replacement, and the commutator itself is subject to wear and maintenance. The commutator assembly on a large machine is a costly element, requiring precision assembly of many parts. There are three types of DC motor:

1. DC series motor

2. DC shunt motor 3. DC compound motor - there are also two types:

1. cumulative compound 2. differentially compounded

Some of the problems of the brushed DC motor are eliminated in the brushless design. In this motor, the mechanical "rotating switch" or commutator/brushgear assembly is replaced by an external electronic switch synchronised to the rotor's position. Brushless motors are typically 85-90% efficient, whereas DC motors with brushgear are typically 75-80% efficient.

Midway between ordinary DC motors and stepper motors lies the realm of the brushless DC motor. Built in a fashion very similar to stepper motors, these often use a permanent magnet external rotor, three phases of driving coils, one or more Hall effect sensors to sense the position of the rotor, and the associated drive electronics.

The coils are activated, one phase after the other, by the drive electronics as cued by the signals from the Hall effect sensors. In effect, they act as three-phase synchronous motors containing their own variable-frequency drive electronics. A specialized class of brushless DC motor controllers utilize EMF feedback through the main phase connections instead of Hall effect sensors to determine position and velocity.

These motors are used extensively in electric radio-controlled vehicles. When configured with the magnets on the outside, these are referred to by modelists as outrunner motors.

Brushless DC motors are commonly used where precise speed control is necessary, as in computer disk drives or in video cassette recorders, the spindles within CD, CD-ROM (etc.) drives, and mechanisms within office products such as fans, laser printers and photocopiers. They have several advantages over conventional motors:

Compared to AC fans using shaded-pole motors, they are very efficient, running much cooler than the equivalent AC motors. This cool operation leads to much-improved life of the fan's bearings.

Without a commutator to wear out, the life of a DC brushless motor can be significantly longer compared to a DC motor using brushes and a commutator. Commutation also tends to cause a great deal of electrical and RF noise; without a commutator or brushes, a brushless motor may be used in electrically sensitive devices like audio equipment or computers.

The same Hall effect sensors that provide the commutation can also provide a convenient tachometer signal for closed-loop control (servo-controlled) applications. In fans, the tachometer signal can be used to derive a "fan OK" signal.

The motor can be easily synchronized to an internal or external clock, leading to precise speed control.

Brushless motors have no chance of sparking, unlike brushed motors, making them better suited to environments with volatile chemicals and fuels. Also, sparking generates ozone which can accumulate in poorly ventilated buildings risking harm to occupants' health.

Brushless motors are usually used in small equipment such as computers and are generally used to get rid of unwanted heat.

They are also very quiet motors which is an advantage if being used in equipment that is affected by vibrations.

Modern DC brushless motors range in power from a fraction of a watt to many kilowatts. Larger brushless motors up to about 100 kW rating are used in electric vehicles. They also find significant use in high-performance electric model aircraft.

Coreless or Ironless DC motors

Nothing in the design of any of the motors described above requires that the iron (steel) portions of the rotor actually rotate; torque is exerted only on the windings of the electromagnets. Taking advantage of this fact is the coreless or ironless DC motor, a specialized form of a brush or brushless DC motor. Optimized for rapid acceleration, these motors have a rotor that is constructed without any iron core.

The rotor can take the form of a winding-filled cylinder inside the stator magnets, a basket surrounding the stator magnets, or a flat pancake (possibly formed on a printed wiring board) running between upper and lower stator magnets.

The windings are typically stabilized by being impregnated with Electrical epoxy potting systems. Filled epoxies that have moderate mixed viscosity and a long gel time.

These systems are highlighted by low shrinkage and low exotherm.

Because the rotor is much lighter in weight (mass) than a conventional rotor formed from copper windings on steel laminations, These motors were commonly used to drive the capstan(s) of magnetic tape drives and are still widely used in high-performance servo-controlled systems, like radio-controlled vehicles/aircraft, humanoid robotic systems, industrial automation, medical devices, etc.

Universal motors

A variant of the wound field DC motor is the universal motor. The name derives from the fact that it may use AC or DC supply current, although in practice they are nearly always used with AC supplies.

The principle is that in a wound field DC motor the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) at the same time, and hence the mechanical force generated is always in the same direction.

In practice, the motor must be specially designed to cope with the AC (impedance must be taken into account, as must the pulsating force), and the resultant motor is generally less efficient than an equivalent pure DC motor.

Operating at normal power line frequencies, the maximum output of universal motors is limited and motors exceeding one kilowatt (about 1.3 horsepower) are rare. But universal motors also form the basis of the traditional railway traction motor in electric railways.

In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies, with 25 and 16.7 hertz (Hz) operation being common. Because they are universal motors, locomotives using this design were also commonly capable of operating from a third rail powered by DC.

The advantage of the universal motor is that AC supplies may be used on motors which have the typical characteristics of DC motors, specifically high starting torque and very compact design if high running speeds are used.

Universal motors generally run at high speeds, making them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high RPM operation is desirable. They are also commonly used in portable power tools, such as drills, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed trimmer motors exceed 10,000 RPM, while Dremel and other similar miniature grinders will often exceed 30,000 RPM.

Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the unit is operated with no significant load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In smaller applications, a fan blade attached to the shaft often acts as an artificial load to limit the motor speed to a safe value, as well as a means to circulate cooling airflow over the armature and field windings.

With the very low cost of semiconductor rectifiers, some applications that would have previously used a universal motor now use a pure DC motor, sometimes with a permanent magnet field

Inside an Electric Motor

Let's start by looking at the overall plan of a simple two-pole DC electric motor. A simple motor has six parts, as shown in the diagram below:

Armature or rotor Commutator Brushes Axle Field magnet

DC power supply of some sort

An electric motor is all about magnets and magnetism: A motor uses magnets to create motion. If you have ever played with magnets you know about the fundamental law of all magnets: Opposites attract and likes repel. So if you have two bar magnets with their ends marked "north" and "south," then the north end of one magnet will attract the south end of the other. On the other hand, the north end of one magnet will repel the north end of the other (and similarly, south will repel south). Inside an electric motor, these attracting and repelling forces create rotational motion.

Motor Image Gallery

Parts of an electric motor..

In the above diagram, you can see two magnets in the motor: The armature (or rotor) is an electromagnet, while the field magnet is a permanent magnet (the field magnet could be an electromagnet as well, but in most small motors it isn't in order to save power).

Toy Motor

The motor being dissected here is a simple electric motor that you would typically find in a toy:

You can see that this is a small motor, about as big around as a dime. From the outside you can see the steel can that forms the body of the motor, an axle, a nylon end cap and two battery leads. If you hook the battery leads of the motor up to a flashlight battery, the axle will spin. If you reverse the leads, it will spin in the opposite direction. Here are two other views of the same motor. (Note the two slots in the side of the steel can in the second shot -- their purpose will become more evident in a moment.)

The nylon end cap is held in place by two tabs that are part of the steel can. By bending the tabs back, you can free the end cap and remove it. Inside the end cap are the motor's brushes. These brushes transfer power from the battery to the commutator as the motor spins:

More Motor PartsThe axle holds the armature and the commutator. The armature is a set of electromagnets, in this case three. The armature in this motor is a set of thin metal plates stacked together, with thin copper wire coiled around each of the three poles of the armature. The two ends of each wire (one wire for each pole) are soldered onto a terminal, and then each of the three terminals is wired to one plate of the commutator. The figures below make it easy to see the armature, terminals and commutator:

The final piece of any DC electric motor is the field magnet. The field magnet in this motor is formed by the can itself plus two curved permanent magnets:

One end of each magnet rests against a slot cut into the can, and then the retaining clip presses against the other ends of both magnets.

Electromagnets and MotorsTo understand how an electric motor works, the key is to understand how the electromagnet works. (See How Electromagnets Work for complete details.)

An electromagnet is the basis of an electric motor. You can understand how things work in the motor by imagining the following scenario. Say that you created a simple electromagnet by wrapping 100 loops of wire around a nail and connecting it to a battery. The nail would become a magnet and have a north and south pole while the battery is connected.

electromagnet would be repelled from the north end of the horseshoe magnet and attracted to the south end of the horseshoe magnet. The south end of the electromagnet would be repelled in a similar way. The nail would move about half a turn and then stop in the position shown.

Electromagnet in a horseshoe magnet

You can see that this half-turn of motion is simply due to the way magnets naturally attract and repel one another. The key to an electric motor is to then go one step further so that, at the moment that this half-turn of motion completes, the field of the electromagnet flips. The flip causes the electromagnet to complete another half-turn of motion. You flip the magnetic field just by changing the direction of the electrons flowing in the wire.

Armature, Commutator and BrushesConsider the image on the previous page. The armature takes the place of the nail in an electric motor. The armature is an electromagnet made by coiling thin wire around two or more poles of a metal core.

The armature has an axle, and the commutator is attached to the axle. In the diagram to the right, you can see three different views of the same armature: front, side and end-on. In the end-on view, the winding is eliminated to make the commutator more obvious. You can see that the commutator is simply a pair of plates attached to the axle. These plates provide the two connections for the coil of the electromagnet.

Armature

The "flipping the electric field" part of an electric motor is accomplished by two parts: the commutator and the brushes.

The diagram at the right shows how the commutator and brushes work together to let current flow to the electromagnet, and also to flip the direction that the electrons are flowing at just the right moment. The contacts of the commutator are attached to the axle of the electromagnet, so they spin with the magnet. The brushes are just two pieces of springy metal or carbon that make contact with the contacts of the commutator.

Armature

Motors Everywhere!

Look around your house and you will find that it is filled with electric motors. Here's an interesting experiment for you to try: Walk through your house and count all the motors you find. Starting in the kitchen, there are motors in:

The fan over the stove and in the microwave oven The dispose-all under the sink The blender The can opener The refrigerator - Two or three in fact: one for the compressor, one for the fan inside

the refrigerator, as well as one in the icemaker The mixer The tape player in the answering machine Probably even the clock on the oven

In the utility room, there is an electric motor in: The washer The dryer The electric screwdriver The vacuum cleaner and the Dustbuster mini-vac The electric saw

Brushes and commutator

The electric drill The furnace blower

Even in the bathroom, there's a motor in: The fan The electric toothbrush The hair dryer The electric razor

Your car is loaded with electric motors: Power windows (a motor in each window) Power seats (up to seven motors per seat) Fans for the heater and the radiator Windshield wipers The starter motor Electric radio antennas

Plus, there are motors in all sorts of other places: Several in the VCR Several in a CD player or tape deck Many in a computer (each disk drive has two or three, plus there's a fan or two) Most toys that move have at least one motor (including Tickle-me-Elmo for its

vibrations) Electric clocks The garage door opener Aquarium pumps

In walking around my house, I counted over 50 electric motors hidden in all sorts of devices. Everything that moves uses an electric motor to accomplish its movement

History and backgroundAt the most basic level, electric motors exist to convert electrical energy into mechanical energy. This is done by way of two interacting magnetic fields -- one stationary, and another attached to a part that can move. A number of types of electric motors exist, but most BEAMbots use DC motors1 in some form or another. DC motors have the potential for very high torque capabilities (although this is generally a function of the physical size of the motor), are easy to miniaturize, and can be "throttled" via adjusting their supply voltage. DC motors are also not only the simplest, but the oldest electric motors.

The basic principles of electromagnetic induction were discovered in the early 1800's by Oersted, Gauss, and Faraday. By 1820, Hans Christian Oersted and Andre Marie Ampere had discovered that an electric current produces a magnetic field. The next 15 years saw a flurry of cross-Atlantic experimentation and innovation, leading finally to a simple DC rotary motor. A number of men were involved in the work, so proper credit for the first DC motor is really a function of just how broadly you choose to define the word "motor."

Michael Faraday (U.K.)

Fabled experimenter Michael Faraday decided to confirm or refute a number of speculations surrounding Oersted's and Ampere's results. Faraday set to work devising an experiment to demonstrate whether or not a current-carrying wire produced a circular magnetic field around it, and in October of 1821 succeeded in demonstrating this.

Faraday took a dish of mercury and placed a fixed magnet in the middle; above this, he dangled a freely moving wire (the free end of the wire was long enough to dip into the mercury). When he connected a battery to form a circuit, the current-carrying wire circled around the magnet. Faraday then reversed the setup, this time with a fixed wire and a dangling magnet -- again the free part circled around the fixed part. This was the first demonstration of the conversion of electrical energy into motion, and as a result, Faraday is often credited with the invention of the electric motor. Bear in mind, though, that Faraday's electric motor is really just a lab demonstration, as you can't harness it for useful work.

Also note that if you plan on repeating this experiment yourself, you should use salt water (or some similar nontoxic but conductive liquid) for the fluid, rather than mercury. Mercury can be very hazardous to your health, and requires stringent precautions on its use. The BBC has instructions

on building just such a device using salt water here.Joseph Henry (U.S.)

It took ten years, but by the summer of 1831 Joseph Henry had improved on Faraday's experimental motor. Henry built a simple device whose moving part was a straight electromagnet rocking on a horizontal axis. Its polarity was reversed automatically by its motion as pairs of wires projecting from its ends made connections alternately with two electrochemical cells. Two vertical permanent magnets alternately attracted and repelled the ends of the electromagnet, making it rock back and forth at 75 cycles per minute.

Henry considered his little machine to be merely a "philosophical toy," but nevertheless believed it was important as the first demonstration of continuous motion produced by magnetic attraction and repulsion. While being more mechanically useful than Faraday's motor, and being the first real use of electromagnets in a

motor, it was still by and large a lab experiment.

For pictures of Henry's motor, as well as more information on his further explorations, check out the Smithsonian Institution's write-up on him (part of the Joseph Henry Papers Project) here.William Sturgeon (U.K.)

Just a year after Henry's motor was demonstrated, William Sturgeon invented the commutator, and with it the first rotary electric motor -- in many ways a rotary analogue of Henry's oscillating motor. Sturgeon's motor, while still simple, was the first to provide continuous rotary motion and contained essentially all the elements of a modern DC motor. Note that Sturgeon used horseshoe electromagnets to produce both the moving and stationary magnetic fields (to be specific, he built a shunt wound DC motor).

The BBC has a good set of instructions on building a replica of this motor

Principles of operationIn any electric motor, operation is based on simple electromagnetism. A current-carrying conductor generates a magnetic field; when this is then placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and to the strength of the external magnetic field. As you are well aware of from playing with magnets as a kid, opposite (North and South) polarities attract, while like polarities (North and North, South and South) repel. The internal configuration of a DC motor is designed to harness the magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion.

Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet or winding with a "North" polarization, while green represents a magnet or winding with a "South" polarization).

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. In most common DC motors (and all that BEAMers will see), the external magnetic field is produced by high-strength permanent magnets1. The stator is the stationary part of the motor -- this includes the motor casing, as well as two or more permanent magnet pole pieces. The rotor (together with the axle and attached commutator) rotate with respect to the stator. The rotor consists of windings (generally on a core), the windings being electrically connected to the commutator. The above diagram shows a common motor layout -- with the rotor inside the stator (field) magnets.

You'll notice a few things from this -- namely, one pole is fully energized at a time (but two others are "partially" energized). As each brush transitions from one commutator contact to the next, one coil's field will rapidly collapse, as the next coil's field will rapidly charge up (this occurs within a few microsecond). We'll see more about the effects of this later, but in the meantime you can see that this is a direct result of the coil windings' series wiring:

There's probably no better way to see how an average DC motor is put together, than by just opening one up. Unfortunately this is tedious work, as well as requiring the destruction of a perfectly good motor.

Luckily for you, I've gone ahead and done this in your stead. The guts of a disassembled Mabuchi FF-030-PN motor (the same model that Solarbotics sells) are available for you to see here (on 10 lines / cm graph paper). This is a basic 3-pole DC motor, with 2 brushes and three commutator contacts.

The use of an iron core armature (as in the Mabuchi, above) is quite common, and has a number of advantages2. First off, the iron core provides a strong, rigid support for the windings -- a particularly important consideration for high-torque motors. The core also conducts heat away from the rotor windings, allowing the motor to be driven harder than might otherwise be the case. Iron core construction is also relatively inexpensive compared with other construction types.

But iron core construction also has several disadvantages. The iron armature has a relatively high inertia which limits motor acceleration. This construction also results in high winding inductances which limit brush and commutator life.

In small motors, an alternative design is often used which features a 'coreless' armature winding. This design depends upon the coil wire itself for structural integrity. As a result, the armature is hollow, and the permanent magnet can be mounted inside the rotor coil. Coreless DC motors have much lower armature inductance than iron-core motors of comparable size, extending brush and commutator life.

Stan Pozmantir ( Location :- Texas)

In 1997-1998 I designed a new type of simple inexpensive brushless motor . It is a reed switch based motor. This motor is very simple but at the same time fast, reliable and efficient. It is also easy to understand its principles of operation. This is how my original project looked:

My second year research was devoted to the further development of this motor. At this time I improved and simplified its design.

For my 1999-2000 project I designed and built 7 more different brushless motors. All of these motors shared a common design, and thus I could easily compare them together. Several of the motors that I used in my project were modified and are now available as kits on this site. They include the transistor controlled reed switch motor, the optointerrupter motor, and the motor based on the Hall effect. These motors were simplified to have the minimum number of parts and to operate as efficiently as possible. 

Theodore Gray

Theodore Gray make a world’s simplest motor

The ingredients (L-R): One ferromagnetic screw, one battery cell, a few inches of copper wire, and a neodymium disk magnet.

I used a drywall screw both because it has a flat head and because it's easy to tell when it's turning. You can use a nail instead. The battery needn't be any particular type; an alkaline C-cell works fine and is easy to hold. Just about any copper wire will work fine for this application. I used some wire with partially stripped (and partially striped) red insulation that is easy to see in the photos. Bare copper will work just as well.

The magnet came from an LED throwie with a dead battery. The best magnets for this job are neodymium disc magnets with a conductive plating.

Set the screw on the magnet, bend the wire.

Attach the magnet to one end of the battery. The weak, single-point contact that you are making serves as an low-friction bearing. I like to attach it to the

button end, but the other end will work as well. (If you do so, the motor will spin the opposite direction. You can also reverse the direction by flipping the magnet up side down.)(Note to physics geeks: The heavier your magnet plus screw system is, the lower the friction will be, right up to the point that magnet isn't strong enough to hold them any more. This is because the friction force is proportional to the normal force. In other words, a bigger magnet is usually better.)

Press and hold the top end of the wire to the top end of the battery, making an electrical connection from the top battery end to the wire.

Here we go: Lightly touch the free end of the wire to the side of the magnet. The magnet and screw start to spin immediately. We can get ours up to 10,000 RPM in about fifteen seconds. Watch out: The screw and magnet can easily fly out of control, and you do not want that screw ending up in your eye. Also note that some of the components, like the wire, can get very warm while you're doing this. Wear safety glasses and use common sense!

Conclusion :-

1) Motors = Generators when operated in reverseA rotor, which is a large coil of wire, is spun in a magnetic field by an electric charge that is delivered to the rotor by the armatures that touch the shaft. The

rotors are connected to the shaft and the armature skips a little bit so that it won’t short out another rotor. Because of this one rotor, of an opposite polarity of the permanent magnetic, is energized at a time; this action caused the rotors to move which rotates the shaft, which means the motor spins.

2) The nature of this thesis is one that leaves little to be analyzed andconcluded. The motor runs satisfactorily and that is the thesis objective.Due to time limitations the motor was not tested in oil insidethe transmission. That has to be done to be able to come to any _nalconclusions. Some things can however be said about the performanceof the system.The switch from a normal to a brushless DC motor does not createany new major problems. Dedicated components help the microcontrollerto handle the more complex control algorithms. The use of thebrushless motor results in a slightly slower system than for a normalDC motor. However, since it has more torque, a good idea would beto change gear reduction to speed up the system. That of course dependingon the speed and torque requirements. The results show that the motor runs at around expected speed and handles theshifting of the driving positions well. The control algorithm performssatisfactorily and is well adjusted to the system.

3) Future Work :-The next natural step will be to build the actuator into the transmission.Then the real system can be tested. After that it is time to build

the transmission into a car and evaluate it. Finally a decision has tobe made, if this is something we want in our future cars. Interestingwould also be to try a brushless motor without hall sensors. That wouldprobably be required if the system is to go into serial production.

References

http://www.howstuffworks.com/motor.htmhttp://www.members.home.net/rdoctors/ http://fly.hiwaay.net/~palmer/motor.html http://www.exploratorium.edu/snacks/stripped_down_motor.htmlhttp://www.hb.quik.com/~norm/motor/http://members.tripod.com/simplemotor/ http://www.qkits.com/serv/qkits/diy/pages/QK77.asphttp://store.jalts.com/elmogekit.html