Each of us has our own early memories of music. An older siblings’ record collection, songs sung in school, the radio Mom always had on in the kitchen. For millions of Americans, these early memories include hymns and other songs of faith, heard in church or at home, and resonating for a lifetime. A recent Gallup poll suggests that as many as 41% of American families regularly attend religious services, and churches continue to be one of the country’s primary sources of live music.
Over the last 25 years, the US has seen a dramatic increase in the number of nondenominational “mega” churches, many of which host large-scale musical events. Still, the majority of churches across the country remain small, relying on members of the congregation to provide musical accompaniment. These members are sometimes professional musicians or music teachers, but they’re also amateurs — recreational musicians who put aside their career and family obligations to make room in their lives for music. Every week, they gather their instruments and raise their voices in worship. The churches and temples in which they perform are as different as the musicians are, but the common threads that unite them — community, music, and faith — are universal.
Phil Grajko (at the microphone) is the music director for Eastern Hills Bible Church in Manlius, New York. The church’s musicians range from the professional, like drummer CV Abdellah, to the novice, like high schooler Chris Cox. Grajko says the music benefits most when each musician is able to find his or her niche, and everyone shares a willingness to get involved
Playing from the Heart
Peter Green, 49, a musician and business consultant from Niagara Falls, New York, grew up with a love of music, learning to play the flute, oboe, French horn, and guitar. As a teenager he began playing in his church, where he met the church’s organist, a young man from Holland who was in the US for school. Green says that the organist’s influence, as well as the changing role of music in his church during those years, acted as a catalyst for him.
“It was the late 1970s, and Catholic churches were beginning to make the shift to what was, at the time, called folk mass,” he recalls. “It was a blend of folk and pop-sounding songs. One night, after we had run through a couple of songs, the organist asked me to avoid the sheet music altogether and just play from the heart. I was terrified!
That terror quickly gave way to inspiration, however, as Green found that he was able to improvise easily with his flute. The result was powerful and uplifting, he says, “almost as if I could pray through the music.” He began playing in various worship-oriented groups, and is still active as a church musician today.
Melany Ethridge, 38, a public relations account executive, has also found great satisfaction in making music on Sundays. Her husband’s career as a church music director has moved her family a number of times, and in each new home, she has found a congregation that is welcoming of and eager for live music. At her current church in Dallas, Texas, she frequently plays clarinet solos or accompanies the offertory portion of the service
“It’s a wonderful creative outlet for me,” she says. “And a wonderful way to worship as well. Being in church gives playing so much more meaning. It’s not just about entertainment or personal fulfillment, it’s about bringing glory to God.”
A Quality Product
The volunteers who give their time and talent each week come from a wide variety of backgrounds and musical abilities, and many have found that it is important to be flexible. Says Paul Witkowski, 43, a pianist who plays at his church in Jacksonville, Florida, “You’re basically working with the talents that people are offering.”
Still, performance quality is important to these musicians, and they work hard to ensure that they’re delivering. “You need to be able to play well enough to keep up with everyone, and to really be a part of the group,” says Ethridge. “The point is to show reverence, to celebrate God. You don’t want to deliver a second-rate product.”
To stay on her game, Ethridge finds time at home to practice her clarinet, but acknowledges that her husband’s work as a musician offers her a bit of an advantage. “It’s probably a little easier for me to find the time,” she says. “We’re a very musical family. So my family is supportive of the time I spend practicing.”
Green also finds time to play at home, and agrees that having a musically-inclined family member does help. “My wife plays with me,” he says. “She plays the mandolin and sings, and we play out several times a month. We rehearse frequently at home.”
Technically speaking, playing in a church environment is not much different from playing in any band or ensemble; the same skills apply. Sight-reading, versatility, working well with others — these are all essential components. But making music as a means of expressing one’s faith has an element all its own. Instead of music being the focus, or the end result, it becomes the medium. Worship, community, and reverence are the ends; the music is the journey.
“To be a church musician takes a very different heart,” says Green. “You can’t measure, or even hope for, what the world calls ’success.’ You can’t count heads, or count collection offerings, and say that’s a sign that you’re reaching people. Sometimes you’re called to reach a room with only four people in it — but if you do reach them, then there’s the success.”
Community of Praise
Whether secular or spiritual, music has a way of bringing people together. Witkowski says that community and diversity are what inspire him to play in his church. As a child in Detroit, he sang with his church’s musical ensemble, continuing the tradition into college. “What was unique about our ensemble was how it became multicultural,” he recalls. “It really embraced the community, and that increased the number of families coming into the church.”
After college, Witkowski moved around a bit, eventually settling in Jacksonville, where he works as the public relations director of the Jacksonville Symphony Orchestra. “The church I play in now is the first African-American Catholic church in Jacksonville,” he says. “I sought the church out after finding that there wasn’t as much diversity elsewhere. It’s something I really enjoy.”
Lonnie Pacelli has become a more involved member of his own church community, returning to the drums after a 20-year hiatus to play at a marriage retreat. “I had played regularly all through college, but after graduation I just stopped,” he says. “When I heard they needed a drummer, I decided to try picking it up again.”
Pacelli, 44, works as an author and business consultant in Sammamish, Washington. His church’s music director heard him playing at the retreat, then asked Pacelli to play at services when their regular drummer left. “At first I resisted,” he recalls. “But eventually I agreed to play. I’m now in rotation with two other drummers, and I play in the church about three times per month.”
Making and strengthening community ties is one of the most rewarding aspects of joining a church ensemble. The musicians often find that they feel more connected to their fellow worshippers, because the goal is not performance, but simply participation.
“We’re a part of something,” explains Green. “Those with the instruments are not ’special’ in the way they would be if they were on a stage somewhere else. We’re simply part of the overall gathering of people who are there to worship together. Some are there with voices, and some are there with instruments meant to help lift those voices. But we’re all there for the same reason.
Making Music is a bimonthly magazine for adult amateur and recreational musicians. Our readers make music simply because they enjoy it—it helps them to relieve stress, connect with their loved ones, and express themselves creatively. Many have played all their lives, while others have only discovered music recently. We publish articles on music theory, practicing and performing techniques, and the health and wellness benefits of playing a musical instrument. Our stories feature real people who find ways to fit music making into their lives, and is intended for musicians of all playing abilities.
Trevor Wye’s famous Practice books for the flute are invaluable to players of every grade, and have received world wide acclaim. This omnibus edition contains practice books 1-5, which includes Tone; Technique; Articulation; Intonation and Vibrato; Breathing and Scales. Each book concentrates on individual areas of flute technique in concise detail. Together, the series forms a complete reference …
Swine Flu Protect Your Family Avoid It And Follow Our 8 Smart Tips To Help
First things first. The straightforward fact of the matter is Swine flu is zip to sneeze at. However, according to health experts, the general public should be vigilant and not panic.
You are probably thinking that is’s easier said than done. Right?
But just keep reading and learn the way to elude this infection and keep you and your family|folks} safe.
The final analysis is the swine influenza outbreak was initially thought to only be broadcast from pigs to humans. Now, studies show that it is being spread through human contact and is quickly becoming one of the most deadly flu viruses of our time.
The CDC ( Center For Disease Control ) and The World Health Organization have been working tirelessly to keep us in the know.informed and updated on confirmed cases and deaths linked to the virus. Here are the details on swine flu symptoms :
1. Runny nose 2. Achy muscles 3. Sleepiness 4 Lack of appetite 5. Sudden onset of fever over 101
As you can obviously see, it is tricky to notice the difference between other sorts of influenza symptoms, so this strain of the virus requires a diagnosis from your well being expert.
It is important that you don’t be concerned, there are a few extremel effective ways to ward off infection and stop the dissemination of swine flu. Listen extraordinarily rigorously now :
One - do not risk it. If you are suffering from flu likesigns, simply remain at home. Since these symptoms mirror regular cold and influenza symptoms, it is better to be safe than regretful.
Two - learn the way to cough and sneeze. Here’s the deal - cough or sneeze into the inside of your elbow on your arm. This is the most effective way to
Three - Wash hands often and entirely. Whatever you touch could be influenced, so a good rule is to keep your hands clean to cut back on your odds of becoming infected.
Four - Antibacterial hand gel works wonders for killing germs, Simply have a tube of hand sanitizer with you at all time. This way you can constantly cleanse your hands.
Five - be careful of public places. Door handles and even ink pens are breeding grounds for germs. Avoid touching them at any price.
Six - Be cautious on airplanes. The close quarters of an airplane is a place where germs like the swine influenza virus lurk so protect yourself.
Seven - Wash your fruit and vegetables entirely. Buy your vegetables and fruit locally if you can. Wash them with water and soak them to increase the effectiveness.
Eight - Telephone Your doctor. If you are experiencing any severeflu like symptoms see your GP straight away. As stated earlier, only your well being practitioner can diagnose your special kind of the flu. Remember not to go in to the doctors surgery without pre-warning them on telephoning as it spreads like wild fire and vulnerable patients may be awaiting appointments in the surgery.
Be aware of what you’ve learned here about the swine influenza. Stay with it and try to protect you and your family to the best of your ability possible . Just by following the simple guiding principles here, you’ll lessen your chances of becoming sick. we hope this helps to give you some ideas on protecting yourself from the swine flu.
My bangs are always so flat and look like theyre flat ironed. I like them better when they look kinda “fluffy” and kind of roll/curl, its flatters my face. But how do i get them from being so flat to better?????
Blow dry your bangs with a roller brush,,,after dry use very large round curling iron and roll it high.
Create Your Own Custom Photobook Or Hard Cover Book
Have you seen those cool PhotoBooks and memory books that are produced by some of the big online photo printing companies? How would you like to be able to produce something like that yourself? Plus you can customize the front to add a full color photograph or title sheet that will really make your books stand out. This is actually something that isn’t all that difficult to you. Here is a quick set of instructions for creating your own fully customized hard cover documents.
First, you will need some materials. Here is what you will need.
* A binding machine capable of binding a hard cover book.
* A cold process laminator / sticker maker (such as the Xyron Creative Station)
* The printed pages to bind into your book.
* A printed page for the cover of your book
* A hard cover case to bind the pages in
Once you have collected these items, you are ready to create your own photobook, memory book or hard cover presentation. Here are five simple steps to finishing your book.
1. Assemble all of the pages of your book and make sure that they are in the correct order. Take the pages and make sure that they are completely square and flush and add end leaves if that is something that is important to you.
2. Insert the pages for your hardcover into the hard cover case that you purchased (probably a Unibind Steelbook, Unibind Photobook or a thermal binding hard cover). Take the cover with your pages in it and place it in the binding machine. The binding machine will heat up the spine of the book and bind your pages in place. If you are using Unibind you are ready to proceed to the next step. If you are using thermal binding you will need to place your document into a special crimper before it is completed. Let the document cool while you proceed with the next step.
3. Now that your document is bound, you need to create the sticker for the front of your cover. At this point you will take your printed page for the cover of your book and run it through your sticker maker / cold process laminator. You are going to want to make sure that your laminator is equipped with a cartridge that adds permanent adhesive to the back side and it is recommended that you add a laminate to the front side (this will prevent peeling or damage).
4. After you have run the document through the laminator, it will have a peel off liner on the back of it much like a sticker does. You will want to peel this liner off and carefully apply it to the front of your book. It is very important to make sure that the sticker is square on the front of the book since the permanent adhesive will make it nearly impossible to adjust later.
5. Once you have applied the sticker to the front of the book you will need to be sure to smooth out the sticker to ensure that there are no air bubbles underneath. After you have done this your customized hard cover book is completed.
For the best results with this type of hard cover binding, I recommend using a glossy white hard cover or trying to match your printed coversheet to the color of your cover. Using this style it is also possible to wrap your printed cover around the spine of the document to add a spine print. You would want to do this after the binding process was complete so that the printing will not be discolored by the heat from the binding system.
About the Author
Jeff McRitchie is the designer and Director of Marketing for www.MyBinding.com
. He has written hundreds of articles on topics related to Binding Machines
, Binding Covers
, Binding Supplies,and more
Ray Wylie Hubbard escaped the demons that devoured his contemporary Townes Van Zandt, but their shadows still flicker through his songs. Eternal and Lowdown is the fifth studio disc in Hubbard’s decade-long comeback; stocked with deeply personal story songs, the preceding four albums were sometimes revelatory but often more than a little, well, heavy. Eternal and Lowdown confronts similar weighty …
The cyber-centric title of Jethro Tull’s 25th collection of new music is cause for pause. Ye olde art-rock band dropping au courant lingo into their songs from the wood? Ian Anderson intoning with characteristic gravity: “Punch my name and in case you wonder / I’ll be yours / Yours dot com”? Hmmm. What would that poor old sod Aqualung think? Get past the notion that these fixtures of prog-rock hav…
The term “romp” could have been invented to describe Royal Flash, a boisterous 1975 comedy-adventure starring Malcolm McDowell (A Clockwork Orange, Caligula) as Captain Harry Flashman: Braggart, bully, coward, thief, womanizer, and all-around scoundrel. Having risen to heroic prominence through sheer luck, Flashman gets sucked into a scheme by German statesman Otto von Bismarck (played with a supe…
I cant take laying in bed anymore!! I have been sick with the flu for 5 days now. Tomorrow is day 6 and i have to go to a couple different places for school. I have to go. Its all day though. Do you think i will be ok for the day? Or can you get a relapse?
Not really; well it depends how you are feeling. I can understand you feeling restless though. I think you will be fine.
If you have a fever then it’s a fer sure no.
Fevers are the only way germs can spread whether it be a high fever or low.
If not then go if you must.
But if you do it’s not something you should just shrug off alright?
Feel better.
Relapse Leaked INFO + Lyrics + New Photos + Eminem Shopping
A person that is considering a Lasik procedure to improve their vision has two major responsibilities: selecting the best surgeon possible for their budget, and understanding and keeping up with eye care after the Lasik operation is done. Most Lasik procedures go very smoothly, and more than 90% of the patients are happy with their improved vision and have no permanent side effects. Part of this success is due to good care at home once the Lasik procedure is complete.
The first step in having the best care after a Lasik procedure is to understand exactly what is directed by the Lasik physician. The prospective Lasik patient should be given a good understanding of the entire process when they first visit a Lasik center to interview the physician and the staff. On the day of the procedure, a member of the staff should very carefully go over exactly what steps should be done to encourage optimal eye health and healing after the Lasik operation.
One thing that the patient should ask is what side effects are to be expected directly after the Lasik procedure, how long they should last, and which symptoms should be promptly told to the Lasik physician or member of the staff. A number of symptoms, such as fluctuating vision or halos around lights, are to be expected and are not a cause of worry. Ask the staff about any postoperative symptoms that are unclear, to make sure that they are thoroughly understood.
Each Lasik physician has their own recommended procedures for their patients, but here is a list of typical suggestions that most Lasik centers recommend. First, get some sleep as soon as possible after the Lasik procedure is done. This gives a great boost to the healing process. Second, avoid any contact, bumping, or rubbing of the eyes for at least five days after the Lasik procedure. Most Lasik centers have some kind of eye guards to wear at night to prevent patients from rubbing their eyes in their sleep.
Third, try to avoid eyestrain for some days after the Lasik procedure. It is tempting to try to read all of the signs and words that were previously blurry, but avoid this temptation at least for the large part. If any light sensitivity or glare is noticed, wear dark sunglasses for several days until this problem resolves itself. Some common Lasik side effects are temporary halos around lights, especially when viewed at night, but this is not a problem to be concerned with.
It is very important to keep the eyes well lubricated in the days following a Lasik operation. Every Lasik physician will give eye drops to help this, and patient should be especially aware of this before going to sleep. A Lasik procedure may increase eye dryness temporarily, and during sleep this may make the eyelid stick slightly to the eye. When the patient wakes up, opening the eyelid is equivalent to rubbing the eye. The physician should be notified if this happens, for there are other varieties of eye drops that will solve this problem.
Taking these simple steps will give nearly all Lasik patients an easy postoperative experience without any problems.
I want to get an advantage of making the first jazz band at my school, i think a second instrument would be helpful, which should i pursue, clarinet or flute?
Since reed books may call for flute or clarinet doubles, the person of whom you should ask this question is that band’s director. Ultimately you would be best served working up skills on both instruments since each could be needed, but consider this- clarinet doubles are more common in the classic big band literature (Ellington, Goodman, Basie, Glenn Miller, et al) and flute is the more common double post 1950. If your band favors one of these directions, go with the corresponding double of choice.
Flute will be easier with regard to fingerings for sax players, but the embouchure for flute and clarinet alike is far different from the saxophone embouchure. Be prepared to study the double of your choice in the mirror.
Nothing is worse than going to cut with your cutlery, and having the handle slip around in your hand. To combat this potential for injury, Victorinox has created this Fibrox santoku knife. The Fibrox® handle is textured and provides a firm grip, even when wet, and does not slip or slide around. It is comfortable and fits naturally to the shape of your hand, and provides an attractive and modern s…
Designed by 11th generation, Maximilian Riedel, these Riedel O Cabernet/Merlot tumblers are reminiscent of the Vinum bowls, only without the stem. Trendy and sophisticated, these tumblers will perform much like Riedel’s preceding wineglass creations, but will also fit easily into the dishwasher or cupboard without the worries of breaking the stem. For those who would like to experience the concept…
Several years ago, an article in Wine Spectator magazine noted the importance of a high-quality glass for improving a wine’s looks and enhancing its bouquet. However, the magazine lamented, many of the attributes that increase the beauty and value of the glass actually obscure the wine. Spiegelau’s Vino Grande series is part of a connoisseur line designed specifically for wine lovers. The thin ri…
Mozart’s opera tells the story of Prince Tamino who rescues Princess Pamino from an evil king with help of Papageno, a bird, and, of course, the magic flute.Genre: Performing Arts - OperaRating: NRRelease Date: 12-DEC-2000Media Type: DVD…
Simple and effective, the Cord Hog Wire Organizer takes loose cables and gives them a safe home for transportation, storage or stationary applications….
Simple and effective, the Cord Hog Wire Organizer takes loose cables and gives them a safe home for transportation, storage or stationary applications….
Fill the womb–I mean, the room–with the gentle sounds of Mozart’s lovely Adagios and Adantes performed by strings and winds.No Track Information AvailableMedia Type: CDArtist: MOZART,W.A.Title: FOR MOTHERS TO BEStreet Release Date: 04/09/1996…
Though Morning View follows hot on the heels of Incubus’s breakthrough single, “Drive,” it doesn’t feel rushed. After all, their previous album, Make Yourself, was released nearly two years ago. Like fellow Los Angeles metal pioneers System of a Down, Incubus find themselves lumped in with the nu-metal fraternity merely because they’re young(ish), angry, and very loud. That’s more than a little un…
Rotating magnetic field as a sum of magnetic vectors from 3 phase coils.
An electric motor converts electrical energy into kinetic energy. The reverse task, that of converting kinetic energy into electrical energy, is accomplished by a generator or dynamo. In many cases the two devices differ only in their application and minor construction details, and some applications use a single device to fill both roles. For example, traction motors used on locomotives often perform both tasks if the locomotive is equipped with dynamic brakes.
Operation
Most electric motors work by electromagnetism, but motors based on other electromechanical phenomena, such as electrostatic forces and the piezoelectric effect, also exist. The fundamental principle upon which electromagnetic motors are based is that there is a mechanical force on any current-carrying wire contained within a magnetic field. The force is described by the Lorentz force law and is perpendicular to both the wire and the magnetic field. Most magnetic motors are rotary, but linear motors also exist. In a rotary motor, the rotating part (usually on the inside) is called the rotor, and the stationary part is called the stator. The rotor rotates because the wires and magnetic field are arranged so that a torque is developed about the rotor’s axis. The motor contains electromagnets that are wound on a frame. Though this frame is often called the armature, that term is often erroneously applied. Correctly, the armature is that part of the motor across which the input voltage is supplied. Depending upon the design of the machine, either the rotor or the stator can serve as the armature.
DC motors
Electric motors of various sizes.
One of the first electromagnetic rotary motors was invented by Michael Faraday in 1821 and consisted of a free-hanging wire dipping into a pool of mercury. A permanent magnet was placed in the middle of the pool of mercury. When a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a circular magnetic field around the wire. This motor is often demonstrated in school physics classes, but brine(salt water) is sometimes used in place of the toxic mercury. This is the simplest form of a class of electric motors called homopolar motors. A later refinement is the Barlow’s Wheel.
Another early electric motor design used a reciprocating plunger inside a switched solenoid; conceptually it could be viewed as an electromagnetic version of a two stroke internal combustion engine.
The modern DC motor was invented by accident in 1873, when Zénobe Gramme connected a spinning dynamo to a second similar unit, driving it as a motor.
The classic DC motor has a rotating armature in the form of an electromagnet. A rotary switch called a commutator reverses the direction of the electric current twice every cycle, to flow through the armature so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the motor. As the poles of the armature electromagnet pass the poles of the permanent magnets, the commutator reverses the polarity of the armature electromagnet. During that instant of switching polarity, inertia keeps the classical motor going in the proper direction. (See the diagrams below.)
A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.
The armature continues to rotate.
When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field. The process then repeats.
Wound field DC motor
The permanent magnets on the outside (stator) of a DC motor may be replaced by electromagnets. By varying the field current it is possible to alter the speed/torque ratio of the motor. Typically the field winding will be placed in series (series wound) with the armature winding to get a high torque low speed motor, in parallel (shunt wound) with the armature to get a high speed low torque motor, or to have a winding partly in parallel, and partly in series (compound wound) for a balance that gives steady speed over a range of loads. Further reductions in field current are possible to gain even higher speed but correspondingly lower torque, called “weak field” operation.
Theory
If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an electric motive force (EMF). This voltage is also generated during normal motor operation. The spinning of the motor produces a voltage known as the back EMF because it opposes the applied voltage on the motor. Therefore the voltage drop across a motor consists of the voltage drop due to this back EMF and the parasitic voltage drop resulting from the internal resistance of the apperature’s windings. The current through a motor is given by the following equation:
I = (Vapplied ? Vbackemf) / Rapperature-
The mechanical power produced by the motor is given by:
P = I * Vbackemf-
Since the back EMF is proportional to motor speed, when an electric motor is first started or is completely stalled, there is zero back EMF. Therefore the current through the apperature is much higher. This high current will produce a strong electric field which will start the motor spinning. As the motor spins, the back EMF increases until it is equal to the applied voltage minus the parasitic voltage drop. At this point there will be a smaller current flowing through the motor. Basically the following three equations can be used to find the speed, current, and back EMF of a motor under a load:
Load = Vbackemf * I-
Vapplied = I * Rapperature ? Vbackemf-
Vbackemf = speed * Fluxapperature-
Speed control
Generally, the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thyristors, transistors, or, formerly, mercury arc rectifiers. In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the “on” to “off” ratio (duty cycle) is varied to alter the average applied voltage, the speed of the motor varies. The percentage “on” time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% “on” time the average voltage at the motor will be 25 V. During the “off” time, current in the motor flows through a diode called a “flywheel diode”. At this point in the cycle the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage “on” time is 100%. At 100% “on” time the supply and motor current are equal. The rapid switching wastes less energy than series resistors. Output filters smooth the average voltage applied to the motor and reduce motor noise. This method is also called pulse width modulation, or PWM, and is often controlled by a microprocessor.
Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for petrol and small diesel engines. Series motors must never be used in applications where the drive can fail (such as belt drives). As the motor accelerates, the armature (and hence field) current reduces. The reduction in field causes the motor to speed up (see ‘weak field’ in the last section) until it destroys itself. This can also be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, the motors can reach speeds far higher than they would do under normal circumstances. This can not only cause problems for the motors themselves and the gears, but due to the differential speed between the rails and the wheels it can also cause serious damage to the rails and wheel treads as they heat and cool rapidly. Field weakening is used in some electronic controls to increase the top speed of an electric vehicle. The simplest form uses a contactor and field weakening resistor, the electronic control monitors the motor current and switches the field weakening resistor in circuit when the motor current reduces below a preset value (this will be when the motor is at its full design speed). Once the resistor is in circuit the motor will increase speed above its normal speed at its rated voltage. When motor current increases the control will disconnect the resistor and low speed torque is made available.
One interesting method of speed control of a DC motor is the Ward Leonard control. It is a method of controlling a DC motor (usually a shunt or compound wound) and was developed as a method of providing a speed-controlled motor from an AC supply, though it is not without its advantages in DC schemes. The AC supply is used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo. The DC output from the armature is directly connected to the armature of the DC motor (usually of identical construction). The shunt field windings of both DC machines are excited through a variable resistor from the generator’s armature. This variable resistor provides extremely good speed control from standstill to full speed, and consistent torque. This method of control was the de facto method from its development until it was superseded by solid state thyristor systems. It found service in almost any environment where good speed control was required, from passenger lifts through to large mine pit head winding gear and even industrial process machinery and electric cranes. Its principal disadvantage was that three machines were required to implement a scheme (five in very large installations, as the DC machines were often duplicated and controlled by a tandem variable resistor). In many applications, the motor-generator set was often left permanently running to avoid the delays that would otherwise be caused by starting it up as required. There are numerous legacy Ward-Leonard installations still in service.
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 current (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 are rare. But universal motors also form the basis of the traditional railway traction motor. In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies with 25 Hz and 16 2/3 hertz 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. The negative aspect is the maintenance and short life problems caused by the commutator. As a result such motors are usually used in AC devices such as food mixers and power tools which are only used intermittently. Continuous speed control of a universal motor running on AC is very easily accomplished using a thyristor circuit while stepped speed control can be accomplished using multiple taps on the field coil. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave DC with half the RMS voltage of the AC power line).
Unlike AC motors, universal motors can easily exceed one revolution per cycle of the mains current. This makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high-speed operation is desired. Many vacuum cleaner and weed trimmer motors will exceed 10,000 RPM, Dremel and other similar miniature grinders will often exceed 30,000 RPM. A theoretical universal motor allowed to operate with no mechanical load will overspeed, which may damage it. In real life, though, various bearing frictions, armature “windage”, and the load of any integrated cooling fan all act to prevent overspeed.
With the very low cost of semiconductor rectifiers, some applications that would have previously used a universal motor now use a pure DC motor, usually with a permanent magnet field. This is especially true if the semiconductor circuit is also used for variable-speed control.
The advantages of the universal motor and alternating-current distribution made installation of a low-frequency traction current distribution system economical for some railway installations. At low enough frequencies, the motor performance is approximately the same as if the motor were operating on DC. Frequencies as low as 162/3 hertz were employed.
AC motors
In 1882, Nikola Tesla identified the rotating magnetic field principle, and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.
Introduction of Tesla’s motor from 1888 onwards initiated what is known as the Second Industrial Revolution, making possible the efficient generation and long distance distribution of electrical energy using the alternating current transmission system, also of Tesla’s invention (1888) [1]. Before the invention of the rotating magnetic field, motors operated by continually passing a conductor through a stationary magnetic field (as in homopolar motors).
Tesla had suggested that the commutators from a machine could be removed and the device could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin to building a perpetual motion machine. [2] Tesla would later attain U.S. Patent 0416194, Electric Motor (December 1889), which resembles the motor seen in many of Tesla’s photos. This classic alternating current electro-magnetic motor was an
induction motor.
Stator energy
Rotor energy
Total energy supplied
Power developed
10
90
90
900
50
50
100
2500
In the induction motor, the field and armature were ideally of equal field strengths and the field and armature cores were of equal sizes. The total energy supplied to operate the device equaled the sum of the energy expended in the armature and field coils.[3] The power developed in operation of the device equaled the product of the energy expended in the armature and field coils. [4]
Michail Osipovich Dolivo-Dobrovolsky later invented a three-phase “cage-rotor” in 1890. A successful commercial polyphase system of generation and long-distance transmission was designed by Almerian Decker at Mill Creek No. 1 [5] in Redlands California.[6]
Components and types
A typical AC motor consists of two parts: 1. An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and; 2. An inside rotor attached to the output shaft that is given a torque by the rotating field.
There are two fundamental types of AC motor depending on the type of rotor used:
The synchronous motor, which rotates exactly at the supply frequency or a submultiple of the supply frequency, and;
The induction motor, which turns slightly slower, and typically (though not necessarily always) takes the form of the squirrel cage motor.
Three-phase AC induction motors
Three phase AC induction motors rated 1 Hp (746 W) and 25 W with small motors from CD player, toy and CD/DVD drive reader head traverse
Where a polyphase electrical supply is available, the three-phase (or polyphase) AC induction motor is commonly used, especially for higher-powered motors. The phase differences between the three phases of the polyphase electrical supply create a rotating electromagnetic field in the motor.
Through electromagnetic induction, the rotating magnetic field induces a current in the conductors in the rotor, which in turn sets up a counterbalancing magnetic field that causes the rotor to turn in the direction the field is rotating. The rotor must always rotate slower than the rotating magnetic field produced by the polyphase electrical supply; otherwise, no counterbalancing field will be produced in the rotor.
Induction motors are the workhorses of industry and motors up to about 500 kW (670 horsepower) in output are produced in highly standardized frame sizes, making them nearly completely interchangeable between manufacturers (although European and North American standard dimensions are different). Very large synchronous motors are capable of tens of thousands of kW in output, for pipeline compressors and wind-tunnel drives. There are two types of rotors used in induction motors.
Squirrel Cage rotors: Most common AC motors use the squirrel cage rotor, which will be found in virtually all domestic and light industrial alternating current motors. The squirrel cage takes its name from its shape - a ring at either end of the rotor, with bars connecting the rings running the length of the rotor. It is typically cast aluminum or copper poured between the iron laminates of the rotor, and usually only the end rings will be visible. The vast majority of the rotor currents will flow through the bars rather than the higher-resistance and usually varnished laminates. Very low voltages at very high currents are typical in the bars and end rings; high efficiency motors will often use cast copper in order to reduce the resistance in the rotor.
In operation, the squirrel cage motor may be viewed as a transformer with a rotating secondary - when the rotor is not rotating in sync with the magnetic field, large rotor currents are induced; the large rotor currents magnetize the rotor and interact with the stator’s magnetic fields to bring the rotor into synchronization with the stator’s field. An unloaded squirrel cage motor at synchronous speed will only consume electrical power to maintain rotor speed against friction and resistance losses; as the mechanical load increases, so will the electrical load - the electrical load is inherently related to the mechanical load. This is similar to a transformer, where the primary’s electrical load is related to the secondary’s electrical load.
This is why, as an example, a squirrel cage blower motor may cause the lights in a home to dim as it starts, but doesn’t dim the lights when its fanbelt (and therefore mechanical load) is removed. Furthermore, a stalled squirrel cage motor (overloaded or with a jammed shaft) will consume current limited only by circuit resistance as it attempts to start. Unless something else limits the current (or cuts it off completely) overheating and destruction of the winding insulation is the likely outcome.
Virtually every washing machine, dishwasher, standalone fan, record player, etc. uses some variant of a squirrel cage motor.
Wound Rotor: An alternate design, called the wound rotor, is used when variable speed is required. In this case, the rotor has the same number of poles as the stator and the windings are made of wire, connected to slip rings on the shaft. Carbon brushes connect the slip rings to an external controller such as a variable resistor that allows changing the motor’s slip rate. In certain high-power variable speed wound-rotor drives, the slip-frequency energy is captured, rectified and returned to the power supply through an inverter.
Compared to squirrel cage rotors, wound rotor motors are expensive and require maintenance of the slip rings and brushes, but they were the standard form for variable speed control before the advent of compact power electronic devices. Transistorized inverters with variable frequency drive can now be used for speed control and wound rotor motors are becoming less common. (Transistorized inverter drives also allow the more-efficient three-phase motors to be used when only single-phase mains current is available, but this is never used in house hold appliances, because it can cause electrical interference and because of high power requirements.)
Several methods of starting a polyphase motor are used. Where the large inrush current and high starting torque can be permitted, the motor can be started across the line, by applying full line voltage to the terminals. Where it is necessary to limit the starting inrush current (where the motor is large compared with the short-circuit capacity of the supply), reduced voltage starting using either series inductors, an autotransformer, thyristors, or other devices are used. A technique sometimes used is star-delta starting, where the motor coils are initially connected in wye for acceleration of the load, then switched to delta when the load is up to speed. This technique is more common in Europe than in North America. Transistorized drives can directly vary the applied voltage as required by the starting characteristics of the motor and load.
This type of motor is becoming more common in traction applications such as locomotives, where it is known as the asynchronous traction motor.
The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:
Ns = 120F / p
where Ns = Synchronous speed, in revolutions per minute F = AC power frequency p = Number of poles per phase winding
Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip that increases with the torque produced. With no load the speed will be very close to synchronous. When loaded, standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated to operate at 100% slip (0 RPM/full stall). The slip of the AC motor is calculated by:
S = (Ns ? Nr) / Ns
where Nr = Rotational speed, in revolutions per minute. S = Normalised Slip, 0 to 1.
As an example, a typical four-pole motor running on 60 Hz might have a nameplate rating of 1725 RPM at full load, while its calculated speed is 1800.
The speed in this type of motor has traditionally been altered by having additional sets of coils or poles in the motor that can be switched on and off to change the speed of magnetic field rotation. However, developments in power electronics mean that the frequency of the power supply can also now be varied to provide a smoother control of the motor speed.
Three-phase AC synchronous motors
If connections to the rotor coils of a three-phase motor are taken out on slip-rings and fed a separate field current to create a continuous magnetic field (or if the rotor consists of a permanent magnet), the result is called a synchronous motor because the rotor will rotate in synchronism with the rotating magnetic field produced by the polyphase electrical supply.
The synchronous motor can also be used as an alternator.
Nowadays, synchronous motors are frequently driven by transistorized variable frequency drives. This greatly eases the problem of starting the massive rotor of a large synchronous motor. They may also be started as induction motors using a squirrel-cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel-cage winding so it has little effect on the synchronous operation of the motor, aside from stabilizing the motor speed on load changes.
Synchronous motors are occasionally used as traction motors; the TGV may be the best-known example of such use.
Two-phase AC servo motors A typical two-phase AC servo motor has a squirrel-cage rotor and a field consisting of two windings: 1) a constant-voltage (AC) main winding, and 2) a control-voltage (AC) winding in quadrature with the main winding so as to produce a rotating magnetic field. The electrical resistance of the rotor is made high intentionally so that the speed-torque curve is fairly linear. Two-phase servo motors are inherently high-speed, low-torque devices, heavily geared down to drive the load.
Single-phase AC induction motors
Three-phase motors inherently produce a rotating magnetic field. However, when only single-phase power is available, the rotating magnetic field must be produced using other means. Several methods are commonly used.
A common single-phase motor is the shaded-pole motor, which is used in devices requiring low torque, such as electric fans or other small household appliances. In this motor, small single-turn copper “shading coils” create the moving magnetic field. Part of each pole is encircled by a copper coil or strap; the induced current in the strap opposes the change of flux through the coil (Lenz’s Law), so that the maximum field intensity moves across the pole face on each cycle, thus producing the required rotating magnetic field.
Another common single-phase AC motor is the split-phase induction motor, commonly used in major appliances such as washing machines and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque by using a special startup winding in conjunction with a centrifugal switch.
In the split-phase motor, the startup winding is designed with a higher resistance than the running winding. This creates an LR circuit which slightly shifts the phase of the current in the startup winding. When the motor is starting, the startup winding is connected to the power source via a set of spring-loaded contacts pressed upon by the not-yet-rotating centrifugal switch. The starting winding is wound with fewer turns of smaller wire than the main winding, so it has a lower inductance (L) and higher resistance (R). The lower L/R ratio creates a small phase shift, not more than about 30 degrees, between the flux due to the main winding and the flux of the starting winding. The starting direction of rotation may be reversed simply by exchanging the connections of the startup winding relative to the running winding.
The phase of the magnetic field in this startup winding is shifted from the phase of the mains power, allowing the creation of a moving magnetic field which starts the motor. Once the motor reaches near design operating speed, the centrifugal switch activates, opening the contacts and disconnecting the startup winding from the power source. The motor then operates solely on the running winding. The starting winding must be disconnected since it would increase the losses in the motor.
In a capacitor start motor, a starting capacitor is inserted in series with the startup winding, creating an LC circuit which is capable of a much greater phase shift (and so, a much greater starting torque). The capacitor naturally adds expense to such motors.
Another variation is the Permanent Split-Capacitor (PSC) motor (also known as a capacitor start and run motor). This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch and the second winding is permanently connected to the power source. PSC motors are frequently used in air handlers, fans, and blowers and other cases where a variable speed is desired. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds. Also provided all 6 winding connections are available separately, a 3 phase motor can be converted to a capacitor start and run motor by commoning two of the windings and connecting the third via a capacitor to act as a start winding.
Repulsion motors are wound-rotor single-phase AC motors that are similar to universal motors. In a repulsion motor, the armature brushes are shorted together rather than connected in series with the field. Several types of repulsion motors have been manufactured, but the repulsion-start induction-run (RS-IR) motor has been used most frequently. The RS-IR motor has a centrifugal switch that shorts all segments of the commutator so that the motor operates as an induction motor once it has been accelerated to full speed. RS-IR motors have been used to provide high starting torque per ampere under conditions of cold operating temperatures and poor source voltage regulation. Few repulsion motors of any type are sold as of 2006.
Single-phase AC synchronous motors
Small single-phase AC motors can also be designed with magnetized rotors (or several variations on that idea). The rotors in these motors do not require any induced current so they do not slip backward against the mains frequency. Instead, they rotate synchronously with the mains frequency. Because of their highly accurate speed, such motors are usually used to power mechanical clocks, audio turntables, and tape drives; formerly they were also much used in accurate timing instruments such as strip-chart recorders or telescope drive mechanisms. The shaded-pole synchronous motor is one version.
Because inertia makes it difficult to instantly accelerate the rotor from stopped to synchronous speed, these motors normally require some sort of special feature to get started. Various designs use a small induction motor (which may share the same field coils and rotor as the synchronous motor) or a very light rotor with a one-way mechanism (to ensure that the rotor starts in the “forward” direction).
Torque motors
A torque motor is a specialized form of induction motor which is capable of operating indefinitely at stall (with the rotor blocked from turning) without damage. In this mode, the motor will apply a steady torque to the load (hence the name). A common application of a torque motor would be the supply- and take-up reel motors in a tape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively-constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches.
Stepper motors
Closely related in design to three-phase AC synchronous motors are stepper motors, where an internal rotor containing permanent magnets or a large iron core with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the motor may not rotate continuously; instead, it “steps” from one position to the next as field windings are energized and deenergized in sequence. Depending on the sequence, the rotor may turn forwards or backwards.
Simple stepper motor drivers entirely energize or entirely deenergize the field windings, leading the rotor to “cog” to a limited number of positions; more sophisticated drivers can proportionally control the power to the field windings allowing the rotors to position “between” the “cog” points and thereby rotate extremely smoothly. Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when part of a digital servo-controlled system.
Stepper motors can be rotated to a specific angle with ease, and hence stepper motors are used in computer disk drives, where the high precision they offer is necessary for the correct functioning of, for example, a hard disk drive or CD drive.
Permanent magnet motor
A permanent magnet motor is the same as the conventional dc machine except the fact that the field winding is replaced by permanent magnets. By doing this, the machine would act like a constant excitation dc machine (separately excited dc machine).
These motors usually have a small rating, ranging up to a few horsepower. They are used in small appliances, battery operated vehicles, for medical purposes, in other medical equipment such as x-ray machines. These motors are also used toys, in automobiles as auxiliary motors for the purposes of seat adjustment, power windows, mirror adjustment and the like.
Brushless DC motors
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.
These problems are eliminated in the brushless motor. In this motor, the mechanical “rotating switch” or commutator/brushgear assembly is replaced by an external electronic switch synchronised to the motor’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 devices 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.
Brushless DC motors are commonly used where precise speed control is necessary, 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 devices 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 okay” signal.
The motor can be easily synchronized to an internal or external clock, leading to precise speed control.
Brushed motors cannot be used in the vacuum of space because they will weld themselves into an immovable position. 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 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 only exerted on the windings of the electromagnets. Taking advantage of this fact is the coreless DC motor, a specialized form of a brush 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 epoxy resins.
Because the rotor is much lighter in weight (mass) than a conventional rotor formed from copper windings on steel laminations, the rotor can accelerate much more rapidly, often achieving a mechanical time constant under 1 ms. This is especially true if the windings use aluminum rather than the heavier copper. But because there is no metal mass in the rotor to act as a heat sink, even small coreless motors must often be cooled by forced air.
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.
Linear motors
A linear motor is essentially an electric motor that has been “unrolled” so that instead of producing a torque (rotation), it produces a linear force along its length by setting up a traveling electromagnetic field.
Linear motors are most commonly induction motors or stepper motors. You can find a linear motor in a maglev (Transrapid) train, where the train “flies” over the ground.
Nano motor
Nanomotor constructed at UC Berkeley. The motor is about 500nm across: 300 times smaller than the diameter of a human hair
Researchers at University of California, Berkeley, have developed rotational bearings based upon multiwall carbon nanotubes. By attaching a gold plate (with dimensions of order 100nm) to the outer shell of a suspended multiwall carbon nanotube (like nested
carbon cylinders), they are able to electrostatically rotate the outer shell relative to the inner core. These bearings are very robust; Devices have been oscillated thousands of times with no indication of wear. The work was done in situ in an SEM. These nanoelectromechanical systems (NEMS) are the next step in miniaturization that may find their way into commercial aspects in the future. Notice: The thin vertical string seen in the middle, is the nanotube to which the rotor is attached. When the outer tube is sheared, the rotor is able to spin freely on the nanotube bearing.
About the Author
Assistant professor in lord venkateswara engineering college.I am doing phd in sathyabama university, Tamil Nadu,India.
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