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THE TECHNOLOGY OF A DC MOTOR

By Leonie Zernitz

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WHAT IS A DC MOTOR? A DC motor relies on the fact that like magnet poles repel and unlike magnetic poles attract each other. A coil of wire with a current running through it generates a electromagnetic field aligned with the center of the coil. By swithcing the current on or off in a coil its magnet field can be switched on or off by switching the direction of the current in the coil the direction of the generated magnetic field can be switched 180 degrees. A simple DC motor typically has a stationary set of magnets in the stator and an armature with a series of two or more windings of wire wrapped in insulated stack slots around iron pole pieces with the ends of the wires terminating on a commutator. The armature includes the mounting bearing that keep it in the center of the motor and the power shaft of the motor and the commutator connections. The winding in the armature continues to loop all the way around the armature and uses either single or parallel conductors, and can circle several times around the stack teeth. The total amound of current sent to the coil, the coil’s size and what it’s wrapped around dictate the strength of the electromagnetic field created. The sequence of turning a particular coil on or off dictates what direction the effective electromagnetic fields are pointed. By turning on and off coils in sequence a rotating magnetic field can be created. These rotating magnetic fields interact with the magnetic fields of the magnets in the stationary part of the motor to create a force on the armature which causes it to rotate. In some DC motor designs the stator fields use electromagnets to create their magnetic fields which allow greater control over the motor. At high power levels, DC motors are almost always cooled using forced air. 2


The commutator allows each armature coil to be activated in turn The current in the coil is typically supplied via two brushes that make moving contact with the commutator. Now, some brushless DC motors have electronics that switch the DC current to each coil on and off and have no brushes to wear out or create sparks. Different number of stator and armature fields as well as how they are connected provide different inherent speed regulation characteristics. The speed of a DC motor can be controlled by changing the voltage applied to the armature. The introduction of variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often controlled by power electronic systems which adjust the voltage by “chopping� the DC current into on and off cycles which have an effective lower voltage.

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Workings of a brushed electric motor with a two-pole rotor (armature) and permanent magnet stator. “N” and “S” designate polarities on the inside faces of the magnets; the outside faces have opposite polarities. The + and - signs show where the DC current is applied to the commutator which supplies current to the armature coils

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BRUSH The brushed DC electric motor generates torque directly from DC power sopplied to the motor by using internal commutation, stationary magnets, and rotating electrical magnets. Advantages of a brushed DC motor include low initial cost, high reliability, and simple control of motor speed. Disadvantages are high maintenance and low life-span for high intensity uses. Maintenance involves regularly replacing the carbon brushes and springs which carry the elctric current, as well as cleaning or replacing the commutator. These components are necessary for transferring electrical power from outside the motor to the spinning wire windings of the rotor inside the motor. Brushes consist of conductors. BRUSHLESS Typical brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical current magnets on the motor housing for the stator, but the symmetrical opposite is also possible. A motor controller converts DC to AC. This design is simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor. Advantages of brushless motors include long life span, little or no maintenance, and high efficiency. Disadvantages include high initial cost, and more complicated motor speed controllers. Some such brushless motors are sometimes referred to as ‘synchronous motors’ although they have no external power supply to be synvhronized with, as would be the case with normal AC synchronous motors.

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This is a brushed DC electric motor generating torque directly from DC power supplied to the motor by using internal commutation, stationary permanent magnets. Torque is produced by the principle of Lorentz force, which states that any current-carrying conductor placed within an external magnetic field experiences a force known as Lorentz force. The commutator consists of a split ring 80 degree shows the effects of having a split ring of different amount of split.

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WHERE IS A DC MOTOR USED FOR? 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. The DC motor was the mainstay of electric traction drives on both electric and diesel electric locomotives, street cars and trams and diesel electric drilling rigs for many years. The introduction of DC motors and an electrical grid system to run machinery startin in the 1870s started a new second Industrial Revolution. DC motors can operate directly from rechargeable batteries, providing the motive power for the first electric vehicles and today’s hybrid cars and electric cars as well as driving a host of cordless tools. Today DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines. If external power is applied to a DC motor it acts as a DC generator, a dynamo. This feature is used to slow down and recharge batteries on hybrid cars and electric cars or to return electricity back to the electric grid used on a street car or electric powered train line when they slow down. This process is called regenerative braking on hybrid and electric cars. In diesel electric locomotives they also use their DC motors as generators to slow down but dissipate the energy in resistor stacks. Newer designs are adding large battery packs to recapture some of this energy.

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HOW IS A DC MOTOR USED IN ART? The DC motor is for example used in the art of Zimoun. He creates soundsculptures of everyday objectst which are connected to the dc motors. This DC motors make the objects move so they get in contact with eachother and create sound. Zimoun is a contemporary artist with a studio located in Bern, Switzerland. He is most known for his sound sculptures, sound architectures and installation art that combine raw, industrial materials such as cardboard boxes, plastic bags, or old furniture, with mechanical elements such as dc-motors. Zimoun blends elements of sound, sculpture, mechanics, and engineering into unique sensory experiences redefining traditional notions of sculpture and sonic performance. Using simple and functional components, Zimoun builds architecturally-minded platforms of sound. Exploring mechanical rhythm and flow in prepared systems, his installations incorporate commonplace industrial objects. In an obsessive display of simple and functional materials, these works articulate a tension between the orderly patterns of Modernism and the chaotic forces of life.

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Zimoun

Zimoun

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HOW DOES IT STIMULATES THE SENSES? The DC motors themselves do not create a big impact, but when a DC motor is combined with other objects it is able to create big impacts. A good example would be, as mentioned before, Zimoun. He creates amazing soundsculptures which are playing with our senses. Zimoun himself; “So I’m not using chance to discover unexpected results, but to elevate the works to a higher level of vitality. I’m intrigued in simple systems to generate and study complex behaviours in sound and motion – the generation and degeneration of patterns. Moreover, in defining and exploring space, simplicity, raw and reduced aesthetics, staging and architectonical elements.” This simplicity he uses for his soundsculptures create a really pragmatic sound which directly grasps our attention. It could almost be described as a form of meditating hypnotisation.

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HOW DOES IT CREATES AN EXPERIENCE? Like said before, not the DC motors itself create a great impact but what can be done with it deffinitly can. How zimoun uses the repitition of DC motors in space and the effects he’s creating are phenomonal. «Rhythm and chaos, silence and noise are some of the opposites that characterize the installations of Swiss Sound Architect Zimoun.The simplicity and complexity of the sculptures form a poetic whole. The attractive visual appeal and the alienating rhythmic sounds are distinctive characteristics of his work. He uses them to reveal a total experience of sound in a new context.» Dots Magazine «Zimoun’s installations are marked by their minimalism: he often uses simple elements such as cardboard boxes, cotton balls, or ventilators in aggregate ways that begin to define an architecture of a different dimension. Coupled with the experiential and spatial sound environment a totally unique experience begins to emerge as one enters his orchestrated architecture.» Katrin Kalden

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«Observing Zimoun’s work opens connections to nature and natural phenomena, physics, quantum mechanics, complexity, simplicity, vitality, individuality, evolvement and growth, but also to industrialization, robotics, mass production and social phenomena, to space, architecture, cosmic white noise, phantasms and highly enjoyable experiences popping up at any moment. Art is supposed to activate and focus our attention. Zimoun’s work seems to be a sweeping and beautiful example for this.» Anton Richter «Zimoun blends elements of sound, sculpture, mechanics, and engineering into unique sensory experiences redefining traditional notions of sculpture and sonic performance.» Ringling Museum of Art «Art that creates these intense, simple experiences is my favorite, it makes you appreciate the universe.» Mitchell Callahan

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WHAT IS THE ADDED VALUE OF USING THIS TECHNIQUE? A DC Motor can really create something within art. When an artist chooses to use a DC motor it will never be about the DC motor itself but more about the extra layer the other part of the artpiece. The part that needs the DC motor to make it move. The value of this technology is very high because a DC motor makes it possible to let objects move on its own, but also to make objects move in groups, after eachother, at the same time or in succession.With this function a lot of effects can be created. I personally am convinced that this expands the possibility of moving art.

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