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The idea that a lower frequency PWM works better simply reflects that the "on" cycle needs to be pretty wide before the motor will draw any current because of moter inductance. A higher PWM frequency will work fine if you hang a large capacitor across the motor or short the motor out on the "off" cycle e.
Then the current that did flow is dissipated as an inductive kick - probably as heat through the flyback diodes. The capacitor integrates the pulse and provides a longer, but lower, current flow through the motor after the driver is cut off. There is not inductive kick either, since the current flow isn't being cut off. Knowing the low pass roll-off frequency of the motor helps to determine an optimum frequency for operating PWM. Try testing your motor with a square duty cycle using a variable frequency, and then observe the drop in torque as the frequency is increased.
This technique can help determine the roll off point as far as power efficiency is concerned. There are also high frequency PWM systems that work. The low versus high frequency for PWM of dc motors describes two totally different approaches. At low frequencies you get a mechanical averaging. When the drive is turned off, there is a momentary spike of voltage that the catch diodes clamp but after that transient dies out the motor is left to freewheel.
You will typically hear the motor buzzing. But this is usually pretty simple to implement with small motors and low voltages remember the motor must freewheel when the drive is off. At high frequencies the inductance of the motor armature does the current averaging. This is similar to a switching power supply or a chopper drive. The catch diodes are more critical here because they carry full motor current a substantial amount of time not so if you are driving the motor locked anti-phase.
High frequency PWM is quite sensitive to the motor properties inductance. For medium size motors usually 20 kHz or higher frequency works. There are also applications where you need PWM controllign for two directions. In those cases you usually combine PWM controlling with H bridge.
There are many ways to do this In locked anti-phase system the motor is always driven either forward or backwards, but always connected to the power. Because the motor is always being driven, it always has a low impedance across it's terminals. No capacitors are needed. The one drawback is intense inductive noise at the switching frequency. Besides "brush-type" DC motors, there is another DC motor type: Brushless DC motors rely on the external power drive to perform the commutation of stationary copper winding on the stator.
This changing stator field makes the permanent magner rotor to rotate. Brushless motors are usually the most expensive type of motor. Electronically commutated, brush-less DC motor systems are widely used as drives for blowers and fans used in electronics, telecommunications and industrial equipment applications. There is wide variety of different brush-less motors for various applications. Some are designed to to rotate at constant speed those used in disk drives and the speed of some can be controlled by varying the voltage applid to them usually the motors used in fans.
Some brushless DC motors have a built-in tachometer which gives out pulses as the motor rotates this applies to both disk drive motors and some computer fans. In general, users select brush-type DC motors when low system cost is a priority, and brushless motors to fulfill other requirements such as maintenance-free operation, high speeds, and explosive environments where sparking could be hazardous.
Brush type DC motors are used in very many battery powered appliances. Brushless DC motors are commonly used in applications like DC powered fans and disk drive rotation motors. The input operating voltage range of the device goes from 7. This web page provides the schematic diagram, the components layout, the PCB layout, the components list or the bill of materials, some pictures of ESC built using the plans, and provide you with other useful information.
Noise is proportional to fan speed. Consider this low-cost, self-contained analog circuit for fan-speed control. You can easily adjust the circuit for any desired linear relationship between the fan voltage and temperature.
Rate this link Circuit forms dc-motor switch with brake - Controlling a small dc motor without speed control sounds like a trivial task; a switch or a relay should suffice. However, several problems accompany this approach. Thic circuit can be useful for designs that don't need precise control of speed and stopping position but can benefit from enhanced deceleration. This circuit is such a controller. A transistor-based H-bridge allows two directions of rotation.
A chopper controls the upper arms of the H-bridge, thereby enabling the speed adjustment. This circuit is designed to work at voltages up to 15V, but can be adapted to higher voltages. Rate this link Circuit provides Class D motor control - Class D amplifier are good candidates for controlling speed and direction in small electric motors.
The standard application circuit for a Class D audio amplifier requires only slight modifications. Full-counterclockwise rotation of the potentiometer corresponds to maximum-speed reverse rotation of the motor.
Midscale on the potentiometer corresponds to motor off, and full-clockwise rotation of the potentiometer produces maximum-speed forward rotation in the motor. The characteristics of a given motor may allow you to eliminate the amplifier's output filter if the circuitry is near the motor.
Rate this link Computer controller for DC motors - This circuit is easy to build and use and it can control two DC motors of any current or voltage rating, depending on the rating of the relays.
The circuit also provides two shaft encoders for positional feedback to the computer. Operates on 5V to 15V. In this way motor torque is maintained. Rate this link DC Motor Controller - controls small 2. This circuit is designed to drive a 48W 24V, 2A motor. The quadrature-output, incremental optical shaft encoder that this Design Idea uses is popular in high-performance, bidirectional, rotation-sensing applications.
Using bigger parts could make it more powerful. This circuit is designed for 24V-dc up to 2. Rate this link Motor controller uses fleapower - A simple, permanent-magnet dc motor is an essential element in a variety of products, such as toys, servo mechanisms, valve actuators, robots, and automotive electronics. In many of these applications, the motor must rotate in a given direction until the mechanism reaches the end of travel, at which point the motor must automatically stop.
This circuit implements a low-cost, micropower, latching motor controller that uses current sensing rather than switches to stop the motor. The design is optimized for a supply voltage of 3 to 9V, making it well-suited to battery-powered applications. Rate this link Nopeudens?? The control signal for this circuit are normal RC servo control pulses.
Rate this link Position detectors provide motor-control logic - Optical sensors determine end of travel, and an SPDT switch selects to which end to send the load. Here are a couple of examples: This circuits connects to a RC car controller servo output. The motor is a medium size permanent magnet type with carbon brushes. The speed controlling on low and medium ranges is implemented using simple series resistors. The battery pack is a pair of AA NiCd cells. The first four data lines are used to control the motors, and the strobe signal from the computer stores the data in latch.
There are two seperate motor driver circuits and each comprises two transistors and two relays. For smaller motors it is usually economically infeasible to buy a commercial speed controller as the cost of the controller will far outstrip the cost of the motor itself.
The PIC's high speed, low cost, and low power requirements lend it to being an inexpensive "smart chip" controller for DC motors. By default, Futaba timings will be used to control the output, however a mechanism shall be provided to calibrate the timings to a specific transmitter.
Rate this link Servo motor control A "servo" is a generic term used for an automatic control system. It comes from the Latin word "servus" - slave. In practical terms, that means a mechanism that you can set and forget, and which adjusts itself during continued operation through feedback.
Servo control is a closed loop control system for electric motors. The motor used in servo control are usually DC motors although AC servo is also possible. Servo control has a feedback circuit which changes the drive power going to motor according the control input signals and the seignal from sensors. Disk drives, for example, contain a servo system insuring that they spin at a desired constant speed by measuring their current rotation, and speeding up or slowing down as necessary to keep that speed.
Many robotics applications contain servo circuits that use motors to position some mechanical parts to desired location. In a servo positioning system the encoder gives the motors position to the servo amplifier and it compares this with the desired position to get the error.
The amplifier then sends current to the servo motor to make the motor move into the proper position, reducing the error. The opearating power fed to the motor is usually controlled usign PWM method. Servo control is usable over varietyof compled motion profiles. Those may involve the following: Because of the additional components such as feedback device usually encoder or tachometer , complexity is considered by some to be the weakness of the closed loop approach.
Those additional components add to the initial cost and complexity of the control system. A typical servo unit consists of a small motor, a gearset, a feedback potentiometer, and some control electronics. There are many applications where there is possible to use servo or stepper motor. While the operating concept is similar, in that they're both able to position an object ot a given orientation, the mechanism of the two is entirely different, and has distinct limitations on the accuracy available when using each type.
To understand which one is better, here are some details of differences between those two: The stepper's resolution is based on the steps typically 1. In the stepper system, the driver advances one step, and the stepper motor follows. For example a a 1. No matter how you gear it, a stepper motor still moves in discrete steps. Each step covers a specific range of "swing". In a nutshell, a stepper with or without gear-train is a set of "preset" positions you can move to.
Any positon that's not part of the "presets" is unattainable by that motor or motor-and-gear-train combination, and can only be reached as an approximation. Stepping motors can be used in simple open-loop control systems; these are generally adequate for systems that operate at low accelerations with static loads, but closed loop control may be essential for high accelerations, particularly if they involve variable loads.
If a stepper in an open-loop control system is overtorqued, all knowledge of rotor position is lost and the system must be reinitialized; servomotors are not subject to this problem. In a servo system the encoder gives the motors position to the servo amplifier and it compares this with the desired position to get the error.
The servo's resolution is based on the encoder attached to it, and the servo amplifier's error. A servo is a motor that can be stopped anywhere you want it, with no "detents" either needed or present. You can turn it to any position you like within its range, of course , and assuming it's been properly "dialed in", it's reasonable to expect that when you say "turn to 4. The term servo motor is used by electric motor manyfacturers to define a motor that is specifically designed to operate in a closed-loop control environment where a feedback device, usually monitoring speed, current, position, etc.
Servo motors are usually designed to be particularly sensitive to the systems control signal voltages, especially at or near zero speed. Circuit measures currents in dc servo motor - This simple circuit design lets you measure all components of a current flowing in a dc servo motor.
Rate this link Controlling RC servos - Servo motors used in radio controlled models cars, planes etc. The servo motors itself have built in motor, gearbox, position feedback mechanism and controlling electronics. The servo motor can be controlled to move any position just by using simple pulse controlling. This handbook is in pdf format. The servo system discussed in this application note uses a PIC17C42 microcontroller, a programmable logic device PLD , and a single-chip H-bridge driver.
Such a system might be used as a positioning controller in a printer, plotter, or scanner. This shaft can be positioned to specific angular positions by sending the servo a coded signal. If you've always been curious about how a servo operates but were afraid to ask , here's a simple description to help you along: Your transmitter makes square wave pulses that vary in length from 1.
Once these pulses are generated, another part of the transmitter converts them into a radio frequency RF signal which is then radiated out through the antenna. The receiver picks up the RF signals from the transmitter and it demodulates extracts the original pulses.
It then sends the extracted pulses to the servos. The servo motor unit circuit board is only happy when the potentiometer pot is set to a certain value for each position of the tx stick. If these values do not match the circuit has a built-in feedback control loop that lets it move the motor which moves the gears, which move the pot to bring things into adjustment. The motion inside servo is imparted to the output arm.
RC servo motors are small motors used in radio controlled models cars, planes etc. The RC servo motors itself have built in motor, gearbox, position feedback mechanism and controlling electronics. Those RC servo motors can be controlled to move any position just by using simple pulse controlling. The control pulse is positive going pulse with length of 1 to 2 ms which is repeated about times a second.
RC servo motors are available in various sizes and with different specifications. The prices vary from motor model to model this kind of motors typically cost around US dollars. Those RC servo motors generally operate form nominally 4. Servo motor shaft can positioned to specific angular positions by sending the servo a coded signal PWM pulse signal. As long as the coded signal exists on the input line, the servo will maintain the angular position of the shaft. As the coded signal changes, the angular position of the shaft changes.
The most common consumer-visible servo is that used to control radio controlled RC model planes, boats, and other gadgets. These are small boxes that contais: The control circuitry notes the difference between the desired position and the current position, and uses the motor to "make it so". Ideally, if the difference in position is large, the motor moves rapidly to the correct position; if the difference is small, the adjustment is more subtle. RC servo motors very useful, besides their original use, in many kinds of small robotics experiments because they ase small, compact and quite inexpensive.
The controlling scheme is very easy to implement with some electronics or some computer software. You can easily build a timer circuit using timer chip for generating suitable controlling pulses or you can use small microcontroller program to do that. Or you can write a program to do that on your PC need some real-time support from operating system if you try this under some multitasking operating system.
After aroud year or so, most of the major brands of RC sevos became compatible with each other. This means you can use any of these brands of servos with any brand of receiver. Somewhere along the line, the wiring didn't become compatible, so your might need to adapt the servo wiring pinout sometimes.
But the signals and signal levels are now standard. When working with servos, you need to keep in mind that the right signal goes to the right servo pin. If you put those in the wrong way, you can burn out either the servo or the receiver or both. The original RC systems are deisgned such that an user can control many servos through one radio controller transmission. In this kind of system each servo pulse will appear sequentially out of the transmitter and this is what you get from the RF receiver.
This is essentially the RF carrier demultiplexed to each servo output. The receiver device then demultiplexes the servo pulses to different servo outputs each output get their right pulse from this pulse stream. The demultiplexer sequencing is reset by a longer pause between eachseries of channels sent, ie a synchronisation period.
Usually all signals are sent in a 20ms time period and the servo signal varies from ms with 1. Besides controlling only RC servo motors, those RC servo control pulses are used to control the RC device main running motor speeds. For this kind of applications the Futaba timings define "neutral" or "no activation" to be uSeconds. Widths less than this amount are considered to be a "reverse" command, widths greater than this amount are considered to be "forward" commands.
A dead zone of 20 uSeconds is defined to exist around neutral, such that any pulse that is within 10uS of neutral wider or narrower shall be considered to be equivalent to a neutral pulse. This specification insures that small variations in the output signal around neutral do not cause motor activation or "jitter. If you do, you'll burn out either the servo or the receiver or both. If you're really good at soldering very small wires, you can reverse the normal direction of servo by swapping the wires that connect directly to the servo motor inside the servo case as well as the little servo wiper that moves as the servo moves.
However, it's a lot easier to buy any of the newer radios; even the cheaper, standard radios these days have servo reversing as a built-in feature of the transmitter. In some applications you can do this kind of reversiing with a small simple servo reversing circuit between the receiver and servo unit. Most RC servo motors work in typical applications at around 5V voltage typically 4. Some servo models will also work on somewhat higher voltages for example up to 6V or more. Most servo manufacturers make their servos look better by advertising the torque and speed ratings at 6 volts or more.
This makes the servos typically stronger and move faster. This means that when you use such servo at normal around 5V, you will not get the full advertised performance. Rate this link Centronics port generates narrow pulse widths - Variable-pulse-width signals are useful in control circuitry for positioning and holding purposes in robotics and power electronics. Frequently, the need arises for pulses with width less than 1 msec. Delays less than 1 msec are usually not available in most programming languages, so generating such pulses can be a problem.
To generate a fractional-millisecond delay you can use a PC's bit timer Counter 2 , which normally controls the PC's speaker. The desired pulse is available at the PC's Centronics port through a buffer stage, which protects the port from overload damage.
Rate this link Controlling Hobby Servos with volts - Generally hobby servo's require a pulse having a variable width from 1 to 2 milli seconds, with 1. This schematic is a simple volt voltage to pulse width circuit. It doesn't get more basic than this, all components are fairly common.
The main draw back is that this circuit is not real linear. A potentiometer controls the servo position. Rate this link How-to: As such the kit provides a text-book example of how a uC can replace a handfull of IC.
Everything is done in software some source code included to text. It receives commands from a host computer via a standard RS serial interface. This circuit supports 4 servo motors and 4 digital outputs. Circuit can be modified for 8 servo motors.
This is a replacement driver board for a standard Tower Hobbies servo using the 6 transistor H-Bridge. Rate this link Servo Chart - Here's a partial list of the major brands of servos and comparative data.
The interface is well defined and the servos are quite affordable, so they are also used for robotics and other clever purposes. It also describes the pinouts of most common servo motor models. Rate this link Simple RC Switch - Simple switch which may be used instead of servo and mechanical micro- switch. Works on all Futaba compatible RC systems.
Rate this link The RC Transmission! Stepper motors consist of a permanent magnet rotating shaft, called the rotor, and electromagnets on the stationary portion that surrounds the motor, called the stator. All of the commutation must be handled externally by the motor controller, and typically, the motors and controllers are designed so that the motor may be held in any fixed position as well as being rotated one way or the other.
To move the rotor the electric magnets on the motor are activated in the right order. Every change in this process moves the motor one step. The order in which those electromagnets are activated determines the rotation direction. If a stepper in an open-loop control system is overtorqued, all knowledge of rotor position is lost and the system must be reinitialized.
Stepping motors come in two varieties, permanent magnet and variable reluctance there are also hybrid motors, which are indistinguishable from permanent magnet motors from the controller's point of view. Lacking a label on the motor, you can generally tell the two apart by feel when no power is applied. Permanent magnet motors tend to "cog" as you twist the rotor with your fingers, while variable reluctance motors almost spin freely although they may cog slightly because of residual magnetization in the rotor.
You can also distinguish between the two varieties with an ohmmeter. Variable reluctance motors usually have three sometimes four windings, with a common return, while permanent magnet motors usually have two independent windings, with or without center taps.
Center-tapped windings are used in unipolar permanent magnet motors. For both permanent magnet and variable reluctance stepping motors, if just one winding of the motor is energised, the rotor under no load will snap to a fixed angle and then hold that angle until the torque exceeds the holding torque of the motor, at which point, the rotor will turn, trying to hold at each successive equilibrium point. Stepping motors come in a wide range of angular resolution. The coarsest motors typically turn 90 degrees per step, while high resolution permanent magnet motors are commonly able to handle 1.
With an appropriate controller, most permanent magnet and hybrid motors can be run in half-steps, and some controllers can handle smaller fractional steps or microsteps. It is possible to achieve micro steps in the order of 10 increments between the native increments. With microstepping there limitations: The divisions generally turn out to be less than totally linear.
For example, with the two coils each half on, you are going to get a position that is just about half way between the two steps, but when you get more near to the ends of the positions, more non-linear the response becomes.
There are lots of factors which effect the error, and most are related to the construction of the motor itself. For applications where precise measuring of a motors' rotor position is critical, a stepper motor is usually the best choice. Stepper motors operate diffrently from other motors; rather than voltage being applied and the rotor spinning smoothly, stepper motors turn on a series of electrical pulses to the motor's windings. Each pulse rotates the rotor by an exact degree.
These pulses are called "steps", hence the name "stepper motor". Stepper motors are traditionally used in various motion control applications. Stepper motors are quite easy to wire and control. Stepper systems are economical to implement, intuitive to control, and have good low speed torque, making them ideal for many low power, computer-controlled applications. They can be for example interfaced to computer using few transitors and made to rotate usign a small piece of software.
Stepper motors provide a good position repeability. Stepper motors are video used in robotics control and in computer accessories disk drives, printers, scanners etc. Stepper motors produce motion in discrete steps. Similar to brushless DC motors, steppers usually have permanent magnets on the rotor and coils on the stator with field movement provided by commutation from the power supply.
Stepper motors are usually controlled by digital signals from the controller to power drive, with one pulse corresponding to one step.
Thus, the frequency of the digital signals controls the speed of the motor. Microstepping is an advanced control method greatly increases the resolution of a stepper motor in applications where hevy high resolution is needed and added complexity is justified. Typical ways to control stepper motor are: They are available in limited power less than one horse power and their rotation speed is limited usually maximum speed limit is about rpm.
The energy effiency of stepper motors is low and stepper motor systems have tendency to have resonances which needs to be avoided.
Stepper motors have characteristic holding torque ability to hold the position and pullout torque ability to move to the next position. Other torques can be difficult to achieve. Therefore, precise torque control is difficult with steppers. Because of open-loop nature of stepper motor controlling, they are not very good to be used with varying loads. It is possible for a stepper motor to loose steps if it is loaded too much. Steppers are not recommended for high-speed or high-power applications, or for applications requiring precise torque control.
The stepper motors typically have a rated voltage at what they can work without overheating. Operating the motor at this voltage limits the maximum speed and torque at high speed. Hi Torque at Top Speed is achieved by over-voltaging the motors with current-limiting. The current limiting can be done by using power resistors or a chopper drive to keep current at the desired level. A Tutorial - This tutorial covers the basic principles of stepping motors and stepping motor control systems, including both the physics of steppers, the electronics of the basic control systems, and software architectures appropriate for motor control.
Rate this link Current Control in Stepper Motors - There are many ways to control current in stepper motors. One of them is to use pulse width modulation PWM to provide constant current drive. Three run modes supported. All contained in an extended D-shell case. Will also accept 4 inputs from external switches. This page has also link the the simple motor driver hardware suitable for the software.
Rate this link Stepper Motor Control program Step - Step is a little utility that allows you to drive up to two 4-phase unipolar stepper motors connected to the parallel port. It can do absolute to a certain angular position or relative clockwise or counter- clockwise by a certain angle movement at every speed. Angles may be measured in steps, degrees or revolutions, and movements can be in wave, two-phase, or half-step mode.
The program documentation includes also the driver hardware circuit diagram and circuit board design. Although this discussion focuses on the early full height IBM drives, most of the points are probably common to most other disk drives. Rate this link Tachmoter related technologies Tachometers are used to evaluate rotational speed, generally in revolutions per minute.
The contact units have a tip that is pressed to the center of the end of a rotating shaft. As the shaft rotates, the tachometer spindle rotates and a gear mechanism accumulates the number of rotations. Non-contact units utilize strobe lights, laser light or infrared technolgy to sense the rotating speed of shafts. These have the distinct advantage of allowing speed measurement without getting close to dangerous rotating machinery.
A tacho generator is, essentially, a small p. However in most applications high accuracy is not actually required so you can use a small motor as a generator.
Any calibration and scaling can be done in the electronic circuitry Other popular method for determining motor speed is pulse rate measutemeent. For this, a sensor measures the rotation of, for instance, a gear wheel.
He was also very adicted to gambling at the time. He lost practically all his savings and then left to USA where he worked for Edison who didn't wan't to hear about AC and the motor too. Then he left and digged the ditches for some time. When he earned enough he constructed the motor, showed it in public and Westinghouse saw it.
They made a contract and the rest is history. As concerns premium efficiency, use of copper in squirrel cage rotors, and other techniques of loss reduction, this is becoming a standard: Feb 1, May or may not be. My references were from books I acquired in or about - before the misinformation highway was free to propagate revisionist stories.
If you wish to convince anyone that copper in rotors is the prevalent technology, please exhibit some order forms with pricing. Research papers do not a product make. As of , I read that the difficulties of separately casting copper was still keeping these motors priced out of the market. However, Tesla Motors uses them, so you should sleep well knowing that they have found a niche.
Feb 2, Wiki page has info as regards both present and future in Europe: New minimum energy performance standards in EU And I know that local manufacturer doesn't make big motors of standard efficiency IE1 anymore. About situation and trends in Asia and America s I can't say anything.
Jim, I've been through the appliance efficiency crunches. They don't mandate anything regarding motors, they just mandate that the system does the same job with less energy.
For air conditioners, we started by putting electronic time delays on the thermostat so that the fan was on an additional seconds. Later, we upgraded to brushless motors in the air handlers because it was the least costly means of obtaining the required numbers.
The motors worked well. So we removed copper and aluminum from the coils until we met the requirement at minimal cost: So Japan uses variable speed compressors and blowers. We tried that experiment as well, adding variable speed compressors to the mix. It was quite a thrill building power factor correction and motor drives for up to 8hp for consumer grade i. Anyway, the marketing didn't support the notion.
I suspect Americans would have bought it if it had an NFL logo The mainstay of American ACs turned to pole-switching or dual compressors designs and though I cried foul at the time, I'm now older and much prefer the latter design.
Well, if a microcontroller hangs up while controlling the drive, then you have about 10 us of shoot through before your IGBTs go to silicon heaven and take the rest with them. Anyway, drives and their motors are not as robust as your good old fashioned Induction motor. Many an AC is still slaving after 20 years.
Most drives are history within As for refrigerators, GE made great inroads by replacing the IIM infinitely inefficient motor used for air circulation with a miniature brushless design.
Less heat delivered into the cooling space translates to less energy to remove: These are essentially foamed silica sealed in an aluminum envelop with the air evacuated. Unfortunately, when they say vacuum, they mean a serious vacuum.
Pumping to 1 torr never made much difference in the lab. Thus slow leakage into the panel can destroy it's usefulness years out Just outside the warranty - darn. The Germans have begun to use vacuum panels in home construction Eeek! I would like the same construction, but only if I had access to replace them easily. With them used in home construction, I'm sure that somebody has already chosen them as the answer to refrigerator energy mandates.
Feb 3, Have something to add?