Sell your car easily then find the best way to search for a new one
A properly looked right after motor automobile is an excellent spot to begin
The specialists say that if you spot and advert to promote your automobile it has to become immaculately clear. People will likely be browsing the photos first and also the text previous, therefore you want your car to stand out and say “hey, search at me, I’m clean”. When the alloys look disgusting as well as the paintwork looks flat, you’ve got no chance of promoting it.
Ensure you’re organised
The best way to shift your car would be to be organised. If a consumer visits your own home or place of perform to view your car for sale then be certain to have the motors details to hand. Items like services heritage, MOTs, receipts of operate completed, logbook and tax data are crucial to a sale; so make sure you discover them all just before the purchaser arrives to get a viewing.
The last thing you would like to be doing is trying to find the logbook although the viewer waits and becomes at any time a lot more aggravated.Regular services are crucial
Is your motor performing not because it ought to? Have you been a bit uneasy when driving it? Nicely, many of the time all an automobile wishes can be a tiny TLC, and by having a servicing check out completed before going up for sale, you will make certain that the customer has little to arrive back again on in regards to how the auto operates. If cash is an problem, just add the services expense onto the price you would like for that automobile. Make sure to inform the purchaser that the motor vehicle has just had a recent service. Most intelligent purchasers want a car which has had a fantastic heritage along with a cared for engine.
Examine every little thing
Preparation is important when preparing your vehicle for sale and 1 of your best suggestions is always to make sure that all issues operate. Check out all the tyre pressures and make sure that they seem to be to be on the appropriate level, as your possible purchaser will desire to test it out around the road, and when your vehicle has incorrect tyre pressures they could sense that it under performs.
If you make use of your brains you’ll be all correct. Preparation is every thing, and provided that you type that out, you have won 50 percent the battle.
Hopefully you’ve discovered this short article regarding how to sell my auto swiftly educational!
Now its time to serach for an used cars…and there is no better place to start than on the internet. Rather than going to well known sites try a search in google for the type of cars you are looking for . Not only will you find thousands of that car for sale across the country but also reviews and opinions on the car in question.
A Novel Analysis of Energy Efficiency Motors and Power Controllers
A novel analysis of energy efficiency motors and power controllers
Voltage Control
Voltage alone can be used as a source of intelligence when the switched capacitors are applied at point where the circuit voltage decreases as circuit load increases. Generally, where they are applied the voltage should decrease as circuit load increases and the drop in voltage should be around 4 – 5 % with increasing load.
Voltage is the most common type of intelligence used in substation applications, when maintaining a particular voltage is of prime importance. This type of control is independent of load cycle. During light load time and low source voltage, this may give leading PF at the substation, which is to be taken note of. KILOVAR Control
Automatic Power Factor Control Relay
It controls the power factor of the installation by giving signals to switch on or off power factor correction capacitors. Relay is the brain of control circuit and needs contactors of appropriate rating for switching on/off the capacitors.
There is a built-in power factor transducer, which measures the power factor of the installation and converts it to a DC voltage of appropriate polarity. This is compared with a reference voltage, which can be set by means of a knob calibrated in terms of power factor.
When the power factor falls below setting, the capacitors are switched on in sequence. The relays are provided with First in First out (FIFO) and First in Last Out (FILO) sequence. The capacitors controlled by the relay must be of the same rating and they are switched on/off in linear sequence. To prevent over correction hunting, a dead band is provided. This setting determines the range of phase angle over which the relay does not respond; only when the PF goes beyond this range, the relay acts. When the load is low, the effect of the capacitors is more pronounced and may lead to hunting. Under current blocking (low current cut out) shuts off the relay, switching off all capacitors one by one in sequence, when load current is below setting. Special timing sequences ensure that capacitors are fully discharged before they are switched in. This avoids dangerous over voltage transient. The solid state indicating lamps (LEDS) display various functions that the operator should know and also and indicate each capacitor switching stage.
Intelligent Power Factor Controller (IPFC)
This controller determines the rating of capacitance connected in each step during the first hour of its operation and stores them in memory. Based on this measurement, the IPFC switches on the most appropriate steps, thus eliminating the hunting problems normally associated with capacitor switching.
Energy Efficient Motors
Minimising Watts Loss in Motors
Improvements in motor efficiency can be achieved without compromising motor performance – at higher cost – within the limits of existing design and manufacturing technology.
From the Table .1, it can be seen that any improvement in motor efficiency must result from reducing the Watts losses. In terms of the existing state of electric motor technology, a reduction in watts losses can be achieved in various ways.
All of these changes to reduce motor losses are possible with existing motor design and manufacturing technology. They would, however, require additional materials and/or the use of higher quality materials and improved manufacturing processes resulting in increased motor cost.
Energy Efficient Motor
Table 1
Thus energy-efficient electric motors reduce energy losses through improved design, better materials, and improved manufacturing techniques. Replacing a motor may be justifiable solely on the electricity cost savings derived from an energy-efficient replacement. This is true if the motor runs continuously, power rates are high, the motor is oversized for the application, or its nominal efficiency has been reduced by damage or previous rewinds. Efficiency comparison for standard and high efficiency motors is shown in Figure 2.
Fig.2
Technical aspect of energy efficiency motors
Energy-efficient motors last longer, and may require less maintenance. At lower temperatures, bearing grease lasts longer; required time between re-greasing increases. Lower temperatures translate to long lasting insulation. Generally, motor life doubles for each 10°C reduction in operating temperature.
Select energy-efficient motors with a 1.15 service factor, and design for operation at 85% of the rated motor load.
Electrical power problems, especially poor incoming power quality can affect the operation of energy-efficient motors.
Speed control is crucial in some applications. In polyphase induction motors, slip is a measure of motor winding losses. The lower the slip, the higher the efficiency. Less slippage in energy efficient motors results in speeds about 1% faster than in standard counterparts.
Starting torque for efficient motors may be lower than for standard motors. Facility managers should be careful when applying efficient motors to high torque applications.
Soft Starter
When starting, AC Induction motor develops more torque than is required at full speed. This stress is transferred to the mechanical transmission system resulting in excessive wear and premature failure of chains, belts, gears, mechanical seals, etc. Additionally, rapid acceleration also has a massive impact on electricity supply charges with high inrush currents drawing +600% of the normal run current.
Soft Starter
The use of Star Delta only provides a partial solution to the problem. Should the motor slow down during the transition period, the high peaks can be repeated and can even exceed direct on line current. Soft starter (see Figure 10.5) provides a reliable and economical solution to these problems by delivering a controlled release of power to the motor, thereby providing smooth, stepless acceleration and deceleration. Motor life will be extended as damage to windings and bearings is reduced. Soft Start & Soft Stop is built into 3 phase units, providing controlled starting and stopping with a selection of ramp times and current limit settings to suit all applications
Soft Starter: Starting current, Stress profile during starting
Advantages of Soft Start –
Less mechanical stress
Improved power factor
Lower maximum demand
Less mechanical maintenance
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General Motors Automotive Service Technicians Train at Centennial College
Opportunities at dealerships continue to increase, with the U.S. Bureau of Labor Statistics expecting job growth in Automotive Service Technology by 14 percent from 2006 through 2016. One such dealership is General Motors. The Automotive Service Technicians employed by General Motors perform many tasks, including: diagnosing problems using General Motors diagnostic equipment as well as performing repairs and preventive maintenance on engines, transmissions, electrical systems, brakes and tires. To carry out their job properly these techs should not only have knowledge of GM cars, but should be able to work with their hands and have enough stamina to be under the car or bending over the hood for extended periods of time. They must also have computer proficiency to work with today’s car computer systems. Training starts with Centennial College’s Automotive Service Technician General Motors of Canada ASEP (MAP 32).
Training for this program is provided at Ontario’s largest automotive training facility. This facility is equipped similarly to a dealership, with General Motors engines, parts and latest technologies. Students work on systems such as electrical, body electrical, engine, transmission, steering, front-end, and all other aspects that would allow a GM vehicle to be serviced. They also study electronics and the diagnosing of computerized control systems. The training for MAP 32 students is actually more in-depth with longer in-school sessions than traditional apprenticeships. This gives them the advantage of having more intensive training, both in and out of school. That’s because every eight weeks, students alternate between the College and their employer for a total of 64 weeks. In the field, practical training is achieved through the apprenticeship aspect of the program. It is during this time that students are employed by a General Motors of Canada dealership and are actually compensated for their work. They train alongside industry professionals and shadow them as they perform their work. Another appealing aspect of the GM apprenticeship is that Centennial College students may be eligible for Employment Insurance during the in-class training portions. General Motors Technician is on high demand.
Applying for this undertaking requires possession of, at minimum, an Ontario Secondary School Diploma or a GED or equivalent. Students are also to be employed by a General Motors dealership. However, if they are not, they may also be selected through an interview process. If you’re interested in the apprenticeship, you may apply directly to the College. The application for the Automotive Service Technician General Motors MAP 32 program is online. Once you’ve successfully been accepted, you’ll have to obtain an employer and register as a MAP apprentice with the Apprenticeship Branch of the Ministry of Training, Colleges and Universities. Acceptance to the GM Automotive Service Tech program is based on successful completion of all entry requirements and space is limited.
Hydraulic Motor
A hydraulic motor is part of a hydraulic drive system that uses pressurized fluid to move a cylinder and make a machine function. An electric motor, combustion engine, or some other type of generator, pressurizes hydraulic fluid through a series of valves and pipes to control the system. This fluid physically pushes either a hydraulic cylinder or motor and drives the machinery. The motor itself is the actuator that converts the fluid’s pressure into torque and rotation.
Gears can be added to a hydraulic motor to change the level of torque administered to a specific operation. For example, a military vehicle that needs to travel over many different types of land will have different gears to control the amount of pressure used to push the hydraulic motor. Pavement will need less hydraulic power to move the vehicle, while dirt or mud may need more.
Different types of plungers or pistons can be used in the motor. The most common type is an axial plunger. The pistons for the motor are designed to be parallel to allow for continuously adjustable sweeps to make the hydraulic motor operate more efficiently. Speed of the hydraulic motor ranges from 1200 to 1800 rpm. In order to increase the speed of a hydraulic motor, radial pistons can be used. These pistons make short sweeps in the engine, allowing for increased speed. However, the maximum level of torque decreases as an effect of these short sweeps.
One of the disadvantages of a hydraulic motor is that it allows for leakage through a connection in the drive system. This helps prevent the engine from locking up as it turns. This means that the motor needs some sort of braking mechanism to ensure that the system remains properly secure. It also requires routine monitoring of gauges that display the fluid levels. A safe operating system is important for the continued use of the machine.
First developed during the 1700s, hydraulic motors are notable for the fact that they can produce more power than other motors of the same size. They can take on larger loads than traditional electric motors and are most commonly used in aircraft, construction vehicles, and automobiles. In addition, a large volume of industrial machinery uses hydraulic motors to perform heavy lifting tasks and in situations that require strong pressurized actions such as injection moulding. These can be constructed as small components to a complex mechanism or one very large hydraulic motor performing a single task.
Finest Motors
Finest Motors Specs
What we notice the most on the 2009 Nissan Murano is the much nicer cabin. Inside, higher-quality materials and an upscale ambience replace the mediocre quality and avant-garde look of the previous interior. New features like a hard-drive-based navigation system and a dedicated iPod interface are also part of the redesign. One thing that didn’t change, however, is the lack of a third-row seat. No doubt, Nissan’s designers felt pressure to add one, as it’s offered on most other competing models. But in a (logical) show of defiance, Nissan felt a third row would be rather small and take up valuable cargo space, especially considering that the Murano is on the smaller side of the midsize crossover segment to begin with.
If you’re interested in this type of vehicle, you’ll find that there are more choices than ever this year. There are larger models to think about, such as the Mazda CX-9 and Toyota Highlander. But the most direct rival to this Nissan is Mazda’s CX-7, as its fun-to-drive factor rates even higher than the Murano’s. However, the CX-7 does give up some practicality due to its relatively meager maximum cargo space, and some may find its turbocharged four-cylinder a little too head-snapping for comfort. Other similar choices include the Ford Edge, the Mitsubishi Outlander V6, the Pontiac Torrent GXP and the Toyota RAV4 V6. These models typically offer more cargo space or passenger capacity, but they don’t offer the same level of athleticism, interior refinement or flair that Nissan’s star performer does.
Not surprisingly, this was pretty much what the first Murano was all about, too. But with a nicer interior and an overall increase in refinement and ability, it seems that Nissan did indeed find a balance that would please even the crew from Cirque du Soleil.
The Z06 (coupe only) largely mirrors the standard model in terms of feature availability, but gains a more powerful V8, a fixed roof, a lighter frame and body panels, larger wheels and tires, a more stiffly tuned suspension, upgraded brakes and special sport seats. Compared to the Z06, the ZR1 boasts a more powerful supercharged V8, plus larger wheels, high-performance carbon-ceramic brakes, an exclusive suspension with adaptive dampers and additional lightweight body panels.
Major stand-alone options, depending on the model, include a navigation system, a transparent roof panel for the coupe, a two-tone interior, a dual-mode exhaust and different wheels. There are also suspension options for the standard Corvettes: the Magnetic Ride Control suspension (which automatically firms up and softens the suspension according to how the car is being driven) and the Z51 performance handling package (which adds extra cooling, stiffer suspension calibrations, bigger brakes, specific tires and shorter gearing for the six-speed manual). Also available are custom color and trim combinations, plus delivery to the Corvette Museum in Bowling Green, Kentucky.
Finest Motors Prices :Body Styles, Trim Levels, and Options
The 2009 Audi TT is available as a 2+2 coupe-styled hatchback or as a two-seater convertible. Trim levels are related to engine size; the 2.0 T is available in three levels and the 3.2 Quattro is available in two. The base Premium TT 2.0 T comes standard with 17-inch alloy wheels, an automatic retractable spoiler, heated side mirrors and windshield washer nozzles, cruise control, a tilt/telescoping multifunction steering wheel, leather seats, full power accessories and a nine-speaker audio system that includes a single-disc CD player, satellite radio and an auxiliary audio jack. The Premium Plus trim adds automatic xenon headlights, daytime running lamps, power front seats, Bluetooth phone connectivity, an auto-dimming interior rearview mirror with a compass, rain-sensing wipers and a trunk pass-through slot with a ski bag. The Prestige trim includes everything on the other trims, plus a navigation system, rear park assist and a Bose premium sound system with a six-CD changer.
Models equipped with the 3.2-liter engine come in the Premium Plus or Prestige trims only. On roadster models, the base 2.0 T trim comes standard with a manually operated soft top; a power top comes standard on all other trim levels.
Packages include an S line sport package that bumps the wheel size to 19 inches and adds special front and rear bumpers, headlight washers, napa leather sport seats and a sport steering wheel. Stand-alone options, depending on the trim level, include 18-inch wheels with high-performance tires, xenon headlights, Bluetooth connectivity, adjustable suspension dampers, satellite radio and upgraded leather upholstery.
Finest Motors Cars
Body Styles, Trim Levels, and Options
The 2009 Toyota Corolla is a compact economy sedan. It’s available in five trim levels — base, LE, S, XLE and XRS. Base Corollas start you out with 15-inch steel wheels, air-conditioning, an MP3/WMA-capable CD stereo with an auxiliary audio jack, a tilt/telescoping steering wheel and power mirrors. The LE gains power windows and locks, along with body-color exterior mirrors. If you select the Corolla S, the LE’s equipment upgrades move to the options list, but you gain 16-inch steel wheels, full underbody spoilers, foglights, sport seats, a leather-wrapped steering wheel and an extra pair of stereo speakers.
Essentially a luxury version of the LE, the new Corolla XLE also gets the 16-inch wheels and upgraded stereo while adding amenities like a sliding center armrest, wood-grain interior trim, electroluminescent gauges, keyless entry and variable intermittent wipers. The top-of-the-line XRS, meanwhile, builds upon the S model’s equipment list. Although it forgoes some of the XLE’s standard conveniences, it adds a larger engine, 17-inch alloy wheels, sport-tuned suspension and steering, a front strut tower brace, a rear deck spoiler and chrome interior trim. Cruise control is also standard on the XRS; it’s optional on other Corollas.
Heated mirrors and satellite radio are optional across the Toyota Corolla line, while the S, XLE and XRS are eligible for a sunroof, an upgraded JBL sound system and a navigation system (with real-time traffic). Leather upholstery is available on the S and XRS only.
Body Styles, Trim Levels, and Options
The 2009 Infiniti FX35 is a midsize luxury crossover SUV available in either rear-wheel drive or AWD. The single well-equipped trim level includes 18-inch alloy wheels, xenon headlights, a power liftgate, leather upholstery, full power accessories, power front seats, a manual tilt/telescoping steering column, cruise control with steering-wheel-mounted switches, dual-zone automatic climate control, a back-up camera, 60/40-split rear seats and an 11-speaker Bose surround audio system with a six-CD changer, an auxiliary audio jack and satellite radio.
Options include a Premium Package, which includes heated and cooled front seats, Bluetooth connectivity, an iPod connector and a power tilt/telescoping steering column. A Deluxe Touring Package (which requires the Premium Package) adds 20-inch alloy wheels, adaptive headlamps and maple wood interior trim. The Navigation Package (which also requires the Premium Package) adds Infiniti’s new hard-drive-based touchscreen navigation system with voice recognition, real-time traffic, a single in-dash CD player (in place of the six-disc changer), a parking system and a four-camera “Around View Monitor” that provides a 360-degree composite image of the vehicle from the outside.
The Technology Package (which requires the Navigation Package — we’re starting to see a pattern here) adds rain-sensing windshield wipers, adaptive cruise control with enhanced capabilities in congested traffic, Intelligent Brake Assist and a lane-departure warning and prevention system. Those who spring for the Technology Package can also add a rear-seat entertainment system. A tow package is available for AWD models only.
Finest Motors New Models :Finest Motors only work with reputable warranty companies that have been in business for years and have excellent track record. They provide great service and you will be provided with a formal contract explaining all the terms and conditions, and the warranty company, not Finest Motors, is solely responsible for all the warranty obligations. Some specialty vehicles will require a surcharge, please call for more details.
Finest Motors Performance 2009 Honda Fit Vehicle Overview
Introduction
On a weekly basis, we auto writer types in the office get weekly reports about what cars are most popular in terms of searches on our site. And for much of 2008, we were amused by reports for “Inside Line,” our dedicated car enthusiast site. One phrase kept coming in as number one. It wasn’t one of the expected ones like, “Nissan GT-R,” “Bitchin’ Camaro” or even “Danica Patrick.” It was, believe it or not, “2009 Honda Fit.”
Sure, we can understand why “normal” car shoppers would be interested in the Fit. This entry-level model, introduced just a couple years ago, quickly became a hit thanks to its high fuel mileage, innovative interior and nimble handling. But car junkies? Either the Fit has suddenly become cooler than a GT-R, or real-world, -dollar-a-gallon gas and everyday practicality have trumped supercar daydreams.
Finest Motors Body Styles, Trim Levels, and Options
The 2009 Toyota Corolla is a compact economy sedan. It’s available in five trim levels — base, LE, S, XLE and XRS. Base Corollas start you out with 15-inch steel wheels, air-conditioning, an MP3/WMA-capable CD stereo with an auxiliary audio jack, a tilt/telescoping steering wheel and power mirrors. The LE gains power windows and locks, along with
Techical Performance of Traction Machine Design
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
Implementation of Stepper Motor in Robot
Implementation of Stepper Motor in Robot
Summary
A typical single axis stepper system consists of a stepper controller, a motor drive, a motor (with or without gearbox), and a power supply. A stepper is typically commanded by two digital inputs: a digital pulse train and a direction bit. The stepping drive and motor is used primarily for position control. And unlike all other motor types, stepper motor is moved in “steps” (just one step per one command pulse) and will hold at its present position if no command pulses are received.
Key words
Step angle, rotor angle, torque, speed.
1. Introduction
The frequency of the pulse train controls the velocity of the motor, where the number of pulses determines the length of the move. The direction signal determines in which direction the motor will rotate. For each pulse from the controller, the drive will move the motor “one step” in the direction indicated by the direction command
The top electromagnet (1) is charged, attracting the topmost four teeth of a sprocket.
The top electromagnet (1) is turned off, and the right electromagnet (2) is charged, pulling the nearest four teeth to the right. This results in a rotation of 3.6°.
The bottom electromagnet (3) is charged; another 3.6° rotation occurs.
The left electromagnet (4) is enabled, rotating again by 3.6°. When the top electromagnet (1) is again charged, the teeth in the sprocket will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation.
A stepper motor is a brushless, syncro electric motor that can divide a full rotation in typically 200 steps.
Of course, this is achieved by increasing the numbers of poles (both on rotor and stator), taking care that they have no common denominator. Additionally, soft magnetic material with many teeth on the rotor and stator cheaply multiplies the number of poles (reluctance motor).Of course, like an AC synchronous motors it is ideally driven by sinusoidal current, allowing a step less operation, but this puts some burden on the controller. When using an 8 bit digital controller 256 micro steps per step are possible. As a analog-to-digital converter produces unwanted ohmic heat in the controller pulse-width modulation is used instead to regulate the mean current.
Simpler models switch voltage only for doing a step needing an extra current limiter. For every step they switch a single cable to the motor. Bipolar controllers can switch between supply voltage, ground, and unconnected. Unipolar controllers can only connect or disconnect a cable, because the voltage is already hard wired. Unipolar controllers need center tapped windings.
Stepper motors are rated by the torque they produce. Syncron electric motors using soft magnetic materials (having a core) have the ability to provide position holding torque while not driven electrically. To achieve full rated torque, the coils in a stepper motor must reach their full rated current during each step. The voltage rating (if there is one) is almost meaningless.
2. Applications
Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when digitally controlled as part of a servo system. Stepper motors are used in floppy disk drives, flatbed scanners, printers, plotters and many more devices. Note that hard drives no longer use stepper motors, instead utilizing a voice coil and servo feedback for head positioning.
3. Construction and Operation
“Can-stack” stepping motors consist of two stacked sets of toothed stator poles and circular coils and a cylindrical ceramic permanent magnet rotor with radial alternating north and south poles. The number of rotor poles is equal the number of stator teeth in each sets of poles.
The stator pole coils are energized; the rotor will align itself between the two equal stator fields. Typically the number of poles is such that the motors have step angles in the range of 7.5 to 20 degrees. A single step of the rotor is the result of a change of magnetic polarity of one set of stator teeth.
This change in polarity is brought about by reversing the direction of current flow in the coil associated with those teeth. The rotor motion for a single step with no load applied is that of a damped oscillation. The damping characteristics are modified by frictional and inertial loading, the sequence in which windings are energized, and the electronic damping in the drive circuitry.
4. Step Angle Accuracy
The average value of the measured step angles of an unloaded stepping motor over 360 degrees will be equal to the nominal step angle. The maximum deviation of the individual steps from the nominal step angle is the error usually specified as a non-cumulative or incremental step angle error. The typical maximum value for this error in a can-stack motor with two phases energized is ± 5%.
5. Stepping Sequences
For continuous rotation a repeating sequence of changing tooth polarity is required. Differences in motor performance characteristics result from different sequences. A commonly used scheme for stepping is to energize both stator coils and to reverse the current in aIternate coils with each successive step. This results in a four step sequence.
Reversing the sequence reverses the direction of rotation. This is called a full step mode with two phases on. It is also possible to step the rotor with the same angular increment by energizing only one phase each step.
This is also a four step sequence and is known as a wave drive. Since only half the copper volume is being used, the efficiency is lower and there is less damping with this scheme than with two phases on. A third sequence alternates between one and two phases energized to produce 1/2 the step angle of the previous sequences. The half step sequence requires eight steps. Angular resolution is improved and the smaller step angel provides an improvement in damping. However, it should also be noted that this scheme produces alternate “weak” steps when only one phase is energized.
Resonance All stepping motors exhibit resonance at certain pulse rates. In typical can-stack stepping motor applications resonances are most commonly encountered at low frequencies (less than 100 pulses per second). Although there is no loss of steps at these frequencies, there is an increase in vibration and noise. This becomes even more noticeable when a gear train is coupled to the motor. When operation at resonant frequencies cannot be avoided, some improvement in damping may be obtained with increased frictional damping, reduced input power, modified drive circuitry or half-stepping.
6. Torque Characteristics
The maximum torque developed by the motor is the static or holding torque. It is measured while displacing the rotor one step with one or two phases energized. During continuous stepping with a constant voltage supply the dynamic torque developed decreases with increasing stepping rate. This reflects the relatively large inductance to resistance ration of the motor.
In the typical dynamic torque curve shown (commonly called an L/R cunve) the lower curve represents the maximum torque load which the motor will start and stop without losing steps (pull-in).
The upper curve represents the maximum torque which the motor can develop at a given pulse rate or alternately, the maximum rate to which a given load can be accelerated (pull-out). Motor torque at higher pulse rates can be increased by increasing the input to the motor using a variety of drive techniques.
These include simple schemes such as increasing the voltage directly or decreasing the time constant by adding external series resistance, and more elaborate techniques such as bi-level voltage drives in which winding current is controlled. When overdriving techniques are used to extend motor performance, consideration must be given to the maximum permissible temperature rise of the motor winding based on the insulation rating of the motor.
Bifilar and Bipolar Operation The terms bifilar and bipolar refer to two different types of windings that may be used in the stator coils. Bipolar windings contain a single coil in each stator half. The switching circuitry used to reverse the direction of current flow with this coil is typically of the full bridge or dual supply type. Bifflar windings contain two coils in each stator half. When they are connected as show in the figure, the magnetic polarity of the stator teeth can be reversed by switching from one coil to the other of each pair with a unipolar supply. Note that although a bifilar-wound motor does contain four coils or “phases,” it is operated as a two phase motor. Bifilar-wound PM steppers are widely used because of the drive circuit simplicity. All stock Hurst stepping motors use this winding configuration. Bifilar and bipolar-wound motors do exhibit some performance differences. Since the winding volume per phase of a bifilar-wound stepper is only half that of a bipolar-wound stepper, the attainable ampere-turns for a given input power will necessarily be lower for the bifilar-wound motor. Therefore, the torque is lower. However, with an L/R drive it is because the bipolar coil with its larger volume will also have a larger time constant. At higher stepping rates the
Open Loop Solutions and Current Limiting for Stepping Motors
There is good reason to run a stepping motor at a supply voltage above that needed to push the maximum rated current through the motor windings. Running a motor at higher voltages leads to a faster rise in the current through the windings when they are turned on, and this, in turn, leads to a higher cutoff speed for the motor and higher torques at speeds above the cutoff.
Microstepping, where the control system positions the motor rotor between half steps, also requires external current limiting circuitry. For example, to position the rotor 1/4 of the way from one step to another, it might be necessary to run one motor winding at full current while the other is run at approximately 1/3 of that current.
The remainder of this section discusses various circuits for limiting the current through the windings of a stepping motor, starting with simple resistive limiters and moving up to choppers and other switching regulators. Most of these current limiters are appropriate for many other applications, including limiting the current through conventional DC motors and other inductive loads.
Resistive Current Limiters
The easiest to understand current limiter is a series resistor. Most motor manufacturers recommended this approach in their literature up until the early 1980′s, and most motor data sheets still give performance curves for motors driven by such circuits. The typical circuits used to control the current through one winding of a permanent magnet or hybrid motor are shown in Figure 4.1.
Figure 4.1
R1 in this figure limits the current through the motor winding. Given a rated current of I and a motor winding with a resistance Rw, Ohm’s law sets the maximum supply voltage as I(Rw+R1). Given that the inductance of the motor motor winding is Lw, the time constant for the motor winding will be Lw/(Rw+R1). Figure 4.2 illustrates the effect of increasing the resistance and the operating voltage on the rise and fall times of the current through one winding of a stepping motor.
Figure 4.2
R2 is shown only in the unipolar example in Figure 4.1 because it is particularly useful there. For a bipolar H-bridge drive, when all switches are turned off, current flows from ground to the motor supply through R1, so the current through the motor winding will decay quite quickly. In the unipolar case, R2 is necessary to equal this performance. When the switches in the H-bridge circuit shown in Figure 4.1 are opened, the direction of current flow through R1 will reverse almost instantaneously! If R1 has any inductance, for example, if it is wire-wound, it must either be bypassed with a capacitor to handle the voltage kick caused by this current reversal, or R2 must be added to the H-bridge.
Given the rated maximum current through each winding and the supply voltage, the resistance and wattage of R1 is easy to compute. R2 if it is included, poses more interesting problems. The resistance of R2 depends on the maximum voltage the switches can handle. For example, if the supply voltage is 24 volts, and the switches are rated at 75 volts, the drop across R2 can be as much as 51 volts without harming the transistors. Given an operating current of 1.5 amps, R2 can be a 34 ohm resistor. Note that an interesting alternative is to use a zener diode in place of R2.
Figuring the peak average power R2 must dissipate is a wonderful exercise in dynamics; the inductance of the motor windings is frequently undocumented and may vary with the rotor position. The power dissipated in R2 also depends on the control system. The worst case occurs when the control system chops the power to one winding at a high enough frequency that the current through the motor winding is effectively constant; the maximum power is then a function of the duty cycle of the chopper and the ratios of the resistances in the circuit during the on and off phases of the chopper. Under normal operating conditions, the peak power dissipation will be significantly lower.
Linear Current Limiters
A pair of high wattage power resistors can cost more than a pair of power transistors plus a heat sink, particularly if forced air cooling is available. Furthermore, a transistorized constant current source, as shown in Figure 4.3, will give faster rise times through the motor windings than the current limiting resistor shown in Figure 4.1. This is because a current source will deliver the full supply voltage across the motor winding until the current reaches the rated current; only then will the current source drop the voltage.
Figure 4.3
In Figure 4.3, a transistorized current source (T1 plus R1) has been substituted for the current limiting resistor R1 used in the examples in Figure 4.1. The regulated voltage supplied to the base of T1 serves to regulate the voltage across the sense resistor R1, and this, in turn, maintains a constant current through R1 so long as any current is allowed to flow through the motor winding. Typically, R1 will have as low a resistance as possible, in order to avoid the high cost of a power resistor. For example, if the forward voltage drops across the diode in series with the base T1 and VBE for T1 are both 0.65 volts, and if a 3.3 volt zener diode is used for a reference, the voltage across R1 will be maintained at about 2.0 volts, so if R1 is 2 ohms, this circuit will limit the current to 1 amp, and R1 must be able to handle 2 watts. R3 in Figure 4.3 must be sized in terms of the current gain of T1 so that sufficient current flows through R1 and R3 to allow T1 to conduct the full rated motor current.
The transistor T1 used as a current regulator in Figure 4.3 is run in linear mode, and therfore, it must dissipate quite a bit of power. For example, if the motor windings have a resistance of 5 ohms and a rated current of 1 amp, and a 25 volt power supply is used, T1 plus R1 will dissapate, between them, 20 watts! The circuits discussed in the following sections avoid this waste of power while retaining the performance advantages of the circuit given here.
When an H-bridge bipolar drive is used with a resistive current limiter, as shown in Figure 4.1, the resistor R2 was not needed because current could flow backwards through R1. When a transistorized current limiter is used, current cannot flow backwards through T1, so a separate current path back to the positive supply must be provided to handle the decaying current through the motor windings when the switches are opened. R2 serves this purpose here, but a zener diode may be substituted to provide even faster turn-off.
The performance of a motor run with a current limited power supply is noticably better than the performance of the same motor run with a resistively limited supply, as illustrated in Figure 4.4:
Figure 4.4
With either a current limited supply or a resistive current limiter, the initial rate of increase of the current through the inductive motor winding when the power is turned on depends only on the inductance of the winding and the supply voltage. As the current increases, the voltage drop across a resistive current limiter will increase, dropping the voltage applied to the motor winding, and therefore, dropping the rate of increase of the current through the winding. As a result, the current will only approach the rated current of the motor winding asymptotically In contrast, with a pure current limiter, the current through the motor winding will increase almost linearly until the current limiter cuts in, allowing the current to reach the limit value quite quickly. In fact, the current rise is not linear; rather, the current rises asymptotically towards a limit established by the resistance of the motor winding and the resistance of the sense resistor in the current limiter. This maximum is usually well above the rated current for the motor winding.
Open Loop Current Limiters
Both the resistive and the linear transistorized current limiters discussed above automatically limit the current through the motor winding, but at a considerable cost, in terms of wasted heat. There are two schemes that eliminate this expense, although at some risk because of the lack of feeback about the current through the motor.
Use of a Voltage Boost
If you plot the voltage across the motor winding as a function of time, assuming the use of a transistorized current limiter such as is illustrated in Figure 4.3, and assuming a 1 amp 5 ohm motor winding, the result will be something like that illustrated in Figure 4.5:
Figure 4.5
As long as the current is below the current limiter’s set point, almost the full supply voltage is applied across the motor winding. Once the current reaches the set point, the voltage across the motor winding falls to that needed to sustain the current at the set point, and when the switches open, the voltage reverses briefly as current flows through the diode network and R2. An alternative way to get this voltage profile is to use a dual-voltage power supply, turning on the high voltage for as long as it takes to bring the current in the motor winding up to the rated current, and then turning off the high voltage and turning on the sustaining voltage. Some motor controllers do this directly, without monitoring the current through the motor windings. This provides excellent performance and minimizes
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