Index

Motor controlling

    Electrical motor control

      AC motors

      AC motors operate from alternating current (AC) power sources. The magnetic fields typically are generated using coils on the rotor and stator, and the field movement occurs naturally in the stator due to the alternating nature of the input power. These motors are inexpensive to build and operate, reliable, and usually run from standard line power. The power supply frequency determines the speed of an AC motor, so if operated from line power, the speed of rotation is always the same. Variable frequency power drives control the speed of AC motors, but such drives are expensive. Different industries use lots of electrical motors in their applications. Electric motor drive systems are estimated to consume over half of all electricity in the United States and over 70% of all electricity in industrial applications.

      It is necessary to design the right motor to the right application. You need a motor that can handle the work you need (gives the speed and power you need), can be powered from the power source you want it to be powered with, can work in the conditions you have and is not too expensive for the application (to buy and maintain). Typically you will need to know the operating power (voltage, freqency, single or three phase), needed motor type and needed power.

      AC induction motor is the most common motor used in industry and mains powered home applicances. Induction motors are also sometimes called squirrel cage motors because the appearance of early rotors. This type of motors are the most common type of industrial AC electric motor, being rugged and requiring neither a separate DC power source nor slip-rings. AC induction motors offer users simple, rugged construction and easy maintenance. An AC induction motor consists of two basic assemblies - stator and rotor - and is analogous to an ac transformer with a rotating secondary. The motor?s name comes from the alternating current (ac) induces into the rotor by the rotating magnetic flux produced in the stator. Motor torque is developed from interaction of currents flowing in the rotor bars and the stator's rotating magnetic field.

      The magnetic field rotates at synchronous speed, the motor's theoretical top speed that would result in no torque output. In actual operation, rotor sped always lags the magnetic field?s speed. Typical slip values range 2-5% at running speed, but can be large at motor startup. Slip also increases with load. The actual rotation speed of AC induction motor depends on the motor design. The rotation direction is controlled on the order of the phases applied to the motor. If you change the order of two phase wires, you can change the rotation direction.

      Induction motors are available in an extremely wide size range from very small units to hundreds of kW. Some common input voltages are 230, 460, and up to 575 V for 60-Hz operation (up to 690 V for 50-Hz-rated units). AC induction motors are designed to run from three phase power.

      Small AC induction motors are also sometimes used in single-phase power applications, and in those applications special arrangements needs to be done to make the motor to start properly and have the righ kind of fields in the running time (this usually needs start capacitors and/or running capacitors). Typically this starting is made with a help of a starting capacitor that is connected for a short time when power is turned on (there are also system which use a "runnign capacitor" that is always connected). A 3 phase motor, once spun up, could continue to run, however, it would develop only 2/3 of horsepower and suffer from unbalanced power that it might have been designed for. So there are cases that with suitable starting arrangement you can run a three phase induction motor with single phase power, but you typically suffer from reduced power rating and reduced starting power. There are also phase converters to convert single phase power to three phase. With a phase converter, a loaded motor could develop 100% of its horsepower, provided that the capacity of phase converter is sufficient.

      Induction motors are practically fixed speed devices. The there is practically only two methods to change the rotation sped of AC induction motor: use frequency converter or use motor with sperate winding for different speeds. In some applciations motors with dual speed winging are used. The applications where accurate speed control is needed, you need s frequency converter. A frequency converter can run a three phase AC motor at very wide speed range quite well (the performance of motor is usually reduced outside it's optimal operation speed).

      There are variable frequency drives that allow induction motors to run on different speeds. But on those applications mechanical load and the speed range must be considered, because on those applications motors can get very hot very fast. The problem is that a 60 Hz (or 50 Hz) motor does not have enough iron in it to allow efficient 25 Hz operation. The motor will run hot due to not having enough inductive reactance at the reduced frequency. Dropping down to 10 Hz would make it even worse. A motor designed for variable frequency drive has more iron. Also, it might use a different iron/steel alloy to allow efficient operation at higher frequencies (say 400 Hz). With a light mechanical load and a good motor combined with a good vraible frequency drive controller, it's sometimes possible to get a reasonable speed range using a variable frequency inverter. A good vriable frequency drive device controls both frequency and voltage. The better ones even take into account that at very low speeds the resistance of the coils cannot be negelected. In VFD (variable frequency drive) system the incoming single phase power is rectified and filtered, and three-phase power is generated from the DC rail using three half-bridges. You get to set the frequency over a range so you can vary the speed of your motor, plus a nice digital display etc. It's a bit harder on the motor insulation than just running it from the line, but well-designed motors should be okay. The reason why VFD is hader for motor insulation is that the unductance in the wiring to the motor allows spikes and ringing at the motor itself. The waveforms that go from VFD to motor are typically quite far from ideal sinewave.

      Frequency converter does not work with AC induction motors that are run from single phase power source, because the operation of the needed motor phase conversion capacitor is very frequency sensitive (works as expeted only at normal mains frequency).

      There are variable frequency drive devices that take in single phase power but can output three-phase power to the three phase motor. The problem in this kind of single phase to three phase VFD is that single phase high power to dc conversion is much more expensive than three phase high power to dc conversion. Filter capacitors have to be much larger with lower ESR. And input power waveform spikes are obscene unless PFC treated. Also, you will need at least three times the current on a single phase line (3 phase power of same amps per line carries about sqrt( 3 ) =~ 1.73 times of power of the same amps on single phase line). The momentary power requirements when motor spins up are much larger.

      An AC induction motor can consume more energy than it actually needs to perform ot's work, particularly when operated at less than full load conditions. This excess energy is given off by the motor in the form of heat. Idling, cyclic, lightly loaded or oversized motors consume more power than required even when they are not working.

      Protection of induction motors is necessary to avoid motor failures when something goes wrong.It is somewhat hard to protect an AC induction motor against overload with normal fuses, because at startup those motors take, for some time, much higher current than is allowed for continuous operation. The thermal overload relays are suitable for overload protoction of AC motor operated on hours duty or uninterrupted duty. There are also more advanced protection relays which provide phase-failure protection, temperature compensation, ON/OFF inidication and manual/automatic reset.In order to reduce the downtime of motors used in industrial plants, high performance circuit breakers can be utilized to switch off and on overheated motors without the need for manual intervention of service personnel.

      There are also other AC motor types than AC induction motors. Here are many different low power motor types. Here is quick overview of them:

      • Permanent Split Capacitor Motors are designed for single speed applications using single phase power. These motors require continuous duty, motor run capacitors connected in the auxiliary winding circuit to produce starting torque. Synchronous designs provide exact speed from No-Load to Full Load, asyncronous motors have regulation uusally less than 3% speed change from No-Load to Full Load.
      • Split Phase motors are designed for single speed applications using single phase power. The specially designed auxiliary winding produces starting torque and is then disconnected by an internal, mechanical, centrifugal starting switch. start or run capacitor is required. However, an electrolytic start capacitor may be connected in series with the auxiliary winding to increase starting torque and reduce starting current.
      • Many AC fans use a shaded-pole motor construction. It is a simple inexpensive single phase AC motor which is generally used for fan applications.
      • Written-Pole motors are special single-phase AC motors which can change the position of magnetic poles while the motor operates.
      • Last but not least is a motor type called "universal motor". It is basically constructed like brush-type DC motor which has both rotor and stator coils. This motor is constructed so that when coils are wired in one way, it rotates to the same direction, no matter if AC or a DC in any direction is applied to it (changing of rotation direction needs changing the connection of coils). Unversal motors are generally used on home appliances and power tools which run on AC power and have wide speed adjustment range. This type of home appliances are for example elecric drills with speed control, vacuum cleaners with power control and some washign machines. The speed of an "universal motor" can be easily controlled using PWM control methods like phase control of AC power.

      In some AC motor applications devices called motor starters are needed.AC motor starters are intended to start and accelerate motors to normalspeed, to ensure continuous operation of motors, and to provideo protection against overloads (switch power of if overload occurs). There are many different type of starters. They all provide protection against overloads (quite often use thermal electrical relays for motor protection,sometimes more advanced electronic circuit). Here is an overvied of most common starter types:

      • Direct-on-line (full-on) AC starters start and accelerare motor to fullspeed by connecting full line voltage immediatly to motor.
      • Reduced voltage AC starters start and accelerate motor to normal speed byconnecting the line voltage to motor in increasing steps.
      • Delta-star starters start three-phase motor in star-connection (reduced start current) and then operate motor at delta wiring (full power).
      • Two-step auto-transformer starters start and accelerate the AC induction motor with rediced torque to normal speed.
      • Rheostatic rotor starters start an AC induction motor by cutting outresistors inserted in the rotor circuit.
      • Some single phase motors use "capacitor start" method. Some of those motors need capacitor start unit which connect the starting capacitor to motor when it is powered up and disconnects that capacitor when the motorhas started.

      Generally electrical motors draw a large current when they started (typically 5-8 times more for starting time, even more for few mains cycles). How large this current is, and how quickly it diminishes depends on the motor type, how its controlled, and what its mechnical load is. A 5HP 240v 3ph motor have a full load rating of about 15 amps but on initial start it may draw 90 amps or more for the brief period of starting time. The mains connector blades have to be able to handle this brief current surge without arcing. To get this working installers sometimes need to goto larger rated plugs which have better contact mating characteristics - hence the HP rating in some mains plugs. Mains plug ratings are really based on current handling capability,a nd the horsepower rating is derived from that, based on the current required by a given size motor to start.

      In some applications where large current and mechanical shock cause by the motor starting is not allowed, soft starters are used to start the motor softly (more expensive alternative to soft starting is using frequncy converter to speed up and control the motor). In soft starter motor terminal voltage is reduced. This will reduce the starting torque, taken current and mechanical shock. Electronics soft starters is are generally implemented so that thyristors reduce the motor terminal voltage in the device by usingphase control principles. This this can achieved by using a pair of thyristors per motor phase. Alternatively for 3 phase motors in some cases spft starting can be made to work with controlling only two of the phases. Siemens claims in their web pages that from a technical point of view, 2 and 3-phase control is almost identical. Soft-starts prevent unnecessary high starting current by reducing the peak current by as much as 50%. A Controlled soft-start limits the inrush of current, prevents unnecessary excess torque and reduces line disturbances on the power distribution system. Soft-starting AC induction motors on power distribution systems with low voltage, or weak capacity, will substantially reduce nuisance trips of circuit breakers and contactors. Across-the-line industrial motor starters are made in sizes up to those capable of carrying 600 amperes. Contacts of power relays used for motor control must be capable of opening at six to eight times the rated steady current in case a motor should stall. The running of the motor can be controlled with a contactor or an electrical circuit. As far as standards are concerned, contactors and soft starters are equivalent. Both are switching devices that enable functional switching.

      Furthermore, a switching device is required that implements a break function. This is usually a circuit-breaker. A motor draws well above run current during start-up, and this needs to be taken into aacount when desiging over current protection for the motor. A fuse or breaker will tolerate overcurrent of a limited amount and duration only before it trips. Again, what exactly it tolerates depends on the characteristics of the breaker/fuse. So whether your motor/breaker combination will run or not depends on a lot more than just the ratio of motor run power to breaker capacity. Note also that breaker characteristics vary a lot between eg US and European countries. European domestic breakers are normally type B, whereas US breakers are closer to our type D, which are a lot more tolerant of overload than type B. The typical US breaker tolerates quite a bit of short-term overload, but for long-term, the overload limit is a lot closer.

      Motor protection circuits for three phase motors usually include also protections against overvoltage, undervoltage and loss of phase. Loss of one mains power phase easily stops the motor and causes it to heat up very much. Small electrical motors (few kW or less) are very sensitive to overvoltage, which easily heats up the motor heavily (this kind of motor is resistance dominating). For small motors a slight undervoltage does not usually cause major problems as long as the voltage is enough to keep it running normally. Some very large (tens to hundreds of kilowatts of power) motors are very sensitive to undervoltage, which heats them heavily.

      In addition to protection and control, some form of reliable method of isolation between the mains network and the motor, to be able to disconnect the power in case of problems exist or the device needs to be repaired. There are many specific safety related regulations on this kind of switching devices. The disconnecting device can be a detecheable plug (like in normal mains equipment) or a special dafety switch of some form. No electronic switching device fulfils this safety requirement, because with them there may also be a measurable and tangible voltage at the motor terminal even if the switching device is switched off and the electronic switchign components generally do not fullfill the strict insulation requirements demanded of safety switches (mechanical switches use many millimeters of isolation between contacts).

      Sometimes it comes need to measure ho much the electrical motor is loaded. To know this, you need to measure the current taken by the motor. This can be made in many ways. But in may applications where load varies somewhat don't think ofusing a digital meter, because when the current fluctuates wildly youwon't be able to read the numbers. This is a case where a pointer instrument scores. It is possible to 'fix' a digital meter to get astable display (you need a special instument or knowledge how to modify a commercial meter).

        Controlling three phase motors

        The actual rotation speed of AC induction motor depends on the motor design. If you want to change that you need to change the frequency of mains voltage (you need special variable speed drive electronics for this) or you need to change the motor. The rotation direction of a three phase motor is controlled on the order of the phases applied to the motor. If you change the order of two phase wires, you can change the rotation direction. Protection of induction motors is necessary to avoid motor failures when something goes wrong.It is somewhat hard to protect an AC induction motor against overload with normal fuses, because at startup those motors take, for some time, much higher current than is allowed for continuous operation. The thermal overload relays are suitable for overload protoction of AC motor operated on hours duty or uninterrupted duty. There are also more advanced protection relays which provide phase-failure protection, temperature compensation, ON/OFF inidication and manual/automatic reset. Modern motor protection devices (usually called electronic thermal overload relays) protect against locked rotor conditions, running overload, high ambient temperature, lost phase and low voltage. Motor protection devices generally use Positive Temperature Coefficient (PTC) sensors to sense motor temperature.

        • Three-phase power regulator - This three-phase linear power regulator can control resistive loads or induction motors. Drive outputs are optoisolated and regulation from zero to full load is via a single potentiometer so interfacing to a PC should be easy, assuming all mains isolation is properly implemented.    Rate this link
        • Solving Motor Failures Due to High Peak Voltages and Fast Rise Times (dv/dt) - The evolution of power semiconductors has been so dramatic that today an insulated gate bi-polar transistor (IGBT) can be turned on in just 0. I micro-second. This results in the voltage rising from zero to peak in only one-tenth of a microsecond. Unfortunately, there are many motors in existence that do not have sufficient insulation to operate under these conditions. When the rise time is very fast the motor insulation system becomes stressed. Excessively high dv/dt can cause premature breakdown of standard motor insulation. Inverter duty motors typically have more phase-to-phase and slot insulation than standard duty motors (NEMA design B).    Rate this link
        • Using VHDL-AMS to model complex heterogeneous systems, part 1 - HDLs bridge the gap between math-based tools and physics-based tools to help you meet model-development requirements. Motion-control-system development poses many challenges for conventional simulation tools. These systems are extremely complex, and they also traverse technology (domain) boundaries as well as analog/digital boundaries. In addition, computers or DSPs control most of these systems in real time, requiring modeling capabilities that encompass both Z-domain transfer functions and software algorithms.    Rate this link

      DC motors

      The direct current (DC) motor is one of the first machines devised to convert electrical power into mechanical power. Permanent magnet (PM) direct current convert electrical energy into mechanical energy through the interaction of two magnetic fields. One field is produced by a permanent magnet assembly, the other field is produced by an electrical current flowing in the motor windings. These two fields result in a torque which tends to rotate the rotor. As the rotor turns, the current in the windings is commutated to produce a continuous torque output. The stationary electromagnetic field of the motor can also be wire-wound like the armature (called a wound-field motor) or can be made up of permanent magnets (called a permanent magnet motor).

      In either style (wound-field or permanent magnet) the commutator. acts as half of a mechanical switch and rotates with the armature as it turns. The commutator is composed of conductive segments (called bars), usually made of copper, which represent the termination of individual coils of wire distributed around the armature. The second half of the mechanical switch is completed by the brushes. These brushes typically remain stationary with the motor's housing but ride (or brush) on the rotating commutator. As electrical energy is passed through the brushes and consequently through the armature a torsional force is generated as a reaction between the motor's field and the armature causing the motor's armature to turn. As the armature turns, the brushes switch to adjacent bars on the commutator. This switching action transfers the electrical energy to an adjacent winding on the armature which in turn perpetuates the torsional motion of the armature.

      Permanent magnet (PM) motors are propably the most commonly usedDC motors, but there are also some other type of DC motors(types which use coils to make the permanent magentic field also).DC motors operate from a direct current power source. Movement of the magnetic field is achieved by switching current between coils within the motor. This action is called "commutation". Very many DC motors (brush-type) have built-in commutation, meaning that as the motor rotates, mechanical brushes automatically commutate coils on the rotor. You can use dc-brush motors in a variety of applications. 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. There are several typical advantages of a PM motor. When compared to AC or wound field DC motors, PM motors are usually physically smaller in overall size and lighter for a given power rating. Furthermore, since the motor's field, created by the permanent magnet, is constant, the relationship between torque and speed is very linear. A PM motor can provide relatively high torque at low speeds and PM field provides some inherent self-braking when power to the motor is shutoff. There are several disadvanges through, those being mostly being high current during a stall condition and during instantaneous reversal. Those can damage some motors or be problematic to control circuitry. Furthermore, some magnet materials can be damaged when subjected to excessive heat and some loose field strength if the motor is disassembled.

      High-volume everyday items, such as hand drills and kitchen appliances, use a dc servomotor known as a universal motor. Those unisversal motors are series-wound DC motors, where the stationary and rotating coils are wires in series. Those motors can work well on both AC and DC power. One of the drawbacks/precautions about series-wound DC motors is that if they are unloaded, the only thing limiting their speed is the windage and friction losses. Some can literally tear themselves apart if run unloaded.

      The term gearmotor is used to define a motor that has a gear reduction system (or gearbox) integrally built into the motor. The gearbox increases the torque generating ability of the motor while simultaneously reducing it's output speed.

      A brushless motor operates much in the same way as a traditional brush motor. However, as the name implies there are no brushes (and no commutator). The mechanical switching function, implemented by the brush and commutator combination in a brush-type motor, is replaced by electronic switching in a brushless motor. In a typical brushless motor the electromagnetic field, created by permanent magnets, is the rotating member of the motor and is called a rotor. The rotatign magnetic field is generated with a number of electromagnets commutatated with electronics switches (typically transistors or FETs) in a right order at right speed. In a brushless motor, the trick becomes to know when to switch the electrical energy in the windings to perpetuate the rotating motion. This is typically accomplished in a brushless-type motor by some feedback means designed to provide an indication of the position of the magnet poles on the rotor relative to the windings. A hall effect device (HED) is a commonly used means for providing this positional feedback. In some applications brushless motors are commutated without sensors or with the use of an encoder for positional feedback. A brushless motor is often used when high reliability, long life and high speeds are required. The bearings in a brushless motor usually become the only parts to wear out. In applications where high speeds are required (usually above 30,000 RPM) a brushless motor is considered a better choice (because as motor speed increases so does the wear of the brushes on traditional motors). A brushless motor's commutation control can easily be separated and integrated into other required electronics, thereby improving the effective power-to-weight and/or power-to-volume ratio. A brushless motor package (motor and commutation controller) will usually cost more than a brush-type, yet the cost can often be made up in other advantages. For example, in applications where sophisticated control of the motor's operation is required. Brushless motors are seen nowadays in very many computer application, they for example rotate normal PC fans, hard disks and disk drives.

      Sometimes the rotation direction needs to be changed. In normal permanent magnet motors, this rotation is changedby changing the polarity of operating power (for example byswitching from negative power supply topositive or by interchangingthe power terminals going to power supply). This directrion chaning is typicaly implemented using relay or a circuit called an H bridge. There are some typical characteristics on "brush-type" DC motors.

      When a DC motor is straight to a battery (with no controller), it draws a large surge current when connected up. The surge is caused because the motor, when it is turning, acts as a generator. The generated voltage is directly proportional to the speed of the motor. The current through the motor is controlled by the difference between the battery voltage and the motor's generated voltage (otherwise called back EMF). When the motor is first connected up to the battery (with no motor speed controller) there is no back EMF. So the current is controlled only by the battery voltage, motor resistance (and inductance) and the battery leads. Without any back emf the motor, before it starts to turn, therefore draws the large surge current. When a motor speed controller is used, it varies the voltage fed to the motor. Initially, at zero speed, the controller will feed no voltage to the motor, so no current flows. As the motor speed controller's output voltage increases, the motor will start to turn. At first the voltage fed to the motor is small, so the current is also small, and as the motor speed controller's voltage rises, so too does the motor's back EMF. The result is that the initial current surge is removed, acceleration is smooth and fully under control.

      Motor speed control of DC motor is nothing new. A simplest method to control the rotation speed of a DC motor is to control it's driving voltage. The higher the voltage is,the higher speed the motor tries to reach. In many applicationsa simple votlage regulation would cause lots of power losson control circuit, so a pulse width modulation method (PWM)is used in many DC motor controlling applications. In the basic Pulse Width Modulation (PWM) method, the operating power to the motors is turned on and off to modulate the current to the motor. The ratio of "on" time to "off" time is what determines the speed of the motor. When doing PWM controlling, keep in mind that a motor is a low pass device. The reason is that a motor is mainly a large inductor. It is not capable of passing high frequency energy, and hence will not perform well using high frequencies. Reasonably low frequencies are required, and then PWM techniques will work. Lower frequencies are generally better than higher frequencies, but PWM stops being effective at too low a frequency. 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.g. power/brake pwm) The reason for this is that short pulses will not allow much current to flow before being cut off. 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. Both are valid. 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. 50% duty cycle has no net current flow and the motor doesn't move. Because the motor is always being driven, it always has a low impedance across it's terminals. A side effect of this is that the motor, at 50%, not only doesn't turn, but it resists turning - it is in brake mode: a low impedance (e.g. a short) is across the 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 motor. 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.A brushless permanent magnet motor is the highest performing motor in terms of torque / vs. weight or efficiency. 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.

        Circuits

        • Build your own 40A Electronic Speed Controller for R/C Models - This is a simple analog yet quite powerful - at least 40A constant current one-way fully proportional electronic speed controller for brushed motors. This one-way controller is therefore not meant for R/C cars or boats where backward run is needed. This circuit is built up using N-channel Power MOSFET's because of their good characteristics (low S-D resistance). The input operating voltage range of the device goes from 7.2 to 19.2 Volts, or from 6 to 16 cells.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.    Rate this link
        • Audio amp makes efficient fan controller - with a simple modification, you can use an audio-amplifier IC to control a fan module    Rate this link
        • Boost converter controls 12V fan from 5V supply - temperature-controlled PWM boost converter allows operation of a 12V brushless dc fan from a 5V supply    Rate this link
        • Circuit generates fan-speed control - Fan noise is becoming a significant issue as electronic equipment increasingly enters the office and the home. 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.    Rate this link
        • Circuits provide 4- to 20-mA PWM control - are useful when you use 4- to 20-mA current-loop signals to control a PWM signal    Rate this link
        • Circuit provides bidirectional, variable-speed motor control - During the development of systems that include small motors, a simple, bidirectional motor controller with speed adjustment may be helpful. 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.    Rate this link
        • DC Motor Speed Controller - Control the speed of any common DC motor rated up to 100V (5A). Operates on 5V to 15V. Uses NE556 to pulse-width modulate a high current switching power transistor, TIP122. In this way motor torque is maintained. Adjustable speed control.    Rate this link
        • DC Motor Controller - controls small 2.5-7V motors, in pdf format, text in Finnish    Rate this link
        • Digital Speed Control for RC car - DC motor PWM controller that takes the 1ms to 2ms pulse from the RC receiver and converts it into a pwm train at 1Khz    Rate this link
        • Encoder and PC make complete motor-control system - This Design Idea combines a simple ISA-bus-resident interface circuit; a garden-variety PC; a high-resolution optical shaft encoder; and a PWM-controlled, 0.05-hp, brushed, permanent-magnet dc motor to make a high-precision and high-power motion-control system. This circuit is designed to drive a 48W (24V, 2A) motor. A different choice of MOSFET in the circuit would allow the system to handle even heavier loads. The quadrature-output, incremental optical shaft encoder that this Design Idea uses is popular in high-performance, bidirectional, rotation-sensing applications.    Rate this link
        • Fan controller adapts to system temperature    Rate this link
        • H-Bridge - This circuit drives small DC motors up to about 100 watts or 5 amps or 40 volts, whichever comes first. Using bigger parts could make it more powerful.    Rate this link
        • H Bridge Motor control - general introduction to H bridges    Rate this link
        • H bridge switch for small motors - simple switch circuit for reversing and stopping a motor without any control of speed    Rate this link
        • H-Bridge Motor Driver - drives small DC motors up to about 100 watts or 5 amps or 40 volts    Rate this link
        • MOSFET switch provides efficient ac/dc conversion - suitable circuit for DC motor powering from AC from transformer    Rate this link
        • Motor controller operates without tachometer feedback - used back-EMF for motor speed controlling to make a voltage controlled motor speed controller    Rate this link
        • Motor-control scheme yields four positions with two outputs - This article shows how to position a mechanical device into four discrete positions but with only two free outputs and one free input from the control system. This circuit is designed for 24V-dc up to 2.5A motor that comes with a worm gear.    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??din tuulettimelle - simle speed controller for PC fan, based on LM317, text in Finnish    Rate this link
        • PCB Drill Controller - uses a Pulse-Width-Modulation technique with current feedback to keep the speed of cheap 12V PCB drills more constant    Rate this link
        • PIC Based Speed Controller - This a a controller which controls a small DC motor to two directions at variable speed. 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.    Rate this link
        • Programmable source powers dc micromotors - a simple, economic, compact, and tricky way of using the LM723 as a programmable voltage source to drive dc micromotors which can can set the output to a value of 200 mV to 6V    Rate this link
        • Pulse Width Modulation DC Motor Control - controls the motor speed by driving the motor with short pulses    Rate this link
        • PWM Motor/Light Controller - 12 or 24V pulse width modulator for light dimming or DC motor controlling    Rate this link
        • PWM Motor/Light Controller Variations - diagrams are for 12V operation and there are high side (common ground) and low side (common +12V) versions    Rate this link
        • PWM speed control - includes theory and some example circuits    Rate this link
        • R/C Switch - This circuit is a so-called "Radio Controlled Electronic Switch". It can be used to switch on/off anything electrical, whatever it is. Here are a couple of examples: navigation lights, landing gear, sound systems, glowplug driver, bomb release, parachute, search lights, gyros, and so on. This circuits connects to a RC car controller servo output.    Rate this link
        • Servo pulse to PWM converter - attemps to be an interface to convert pulses from R/C receiver to a dual PWM(Pulse Width Modulation) signal required by an H-bridge    Rate this link
        • Simple PWM controller - 555 timer based PWM motor control project for electric fan or other DC motor    Rate this link
        • Simple ?C acts as dedicated motor control - PIC16C84 circuit accepts control words from an 8-bit digital bus and controls motor    Rate this link
        • Electric Toothbrush with Inductively Coupled Charger - For the toothbrush, a 4 position switch selects between Off, Low, Medium, and High. 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.    Rate this link
        • Computer controller for DC motors - The motor control circuit is connected to an IBM PC parallel port, via U1, a 74LS192 four-bit latch. 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.    Rate this link
        • PIC Based Speed Controller - Real world applications often call for controlling small to medium sized DC motors from digital circuits. 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.    Rate this link
        • Servo pulse to PWM converter - The circuit presented on this page attemps to be an interface to convert pulses such as provided by a Basic Stamp or R/C receiver to a dual PWM(Pulse Width Modulation) signal required by an H-bridge.    Rate this link
        • Electronic Speed Control - The ESC Module shall have as input an R/C servo signal, and shall generate a modulated pulse whose width and polarity are proportional to width of that signal. 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). The servo system uses a sensor to sense motor position/speed. 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: control of either velocity and/or position; high resolution and accuracy; velocity may be either very slow, or very high; and the application may demand high torques in a small package size. 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. Servo motors are typically controlled with analogue control interface, most often using +-10V control signal, but there are also ther options available (current loop, digital numerical control etc. on some devices).

      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 1.8 deg or 3.6 deg per step). In the stepper system, the driver advances one step, and the stepper motor follows. For example a a 1.8 deg. stepper will turn a full circle in 200 steps. 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 amplifier then sends current to the servo motor to make the motor move into the proper position, reducing 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 4.6 degrees" and punch the "go" button, it's going to turn whatever it controls to point at a reasonable approximation of 4.6 degrees.

      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. is used to control the performance of the motor. Servo motors are usually designed to be particularly sensitive to the systems control signal voltages, especially at or near zero speed.

      RC servo control circuits

      A Servo is a small device that has an output shaft. 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 1.0 to 2.0 miliseconds depending on the position of each control stick. 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 50-60 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 15-20 US dollars). Those RC servo motors generally operate form nominally 4.8V power source (somewhat higher and lower voltages are usually OK for those motor, there are for example models that can operate at 6V). 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:

      • a motor (small low voltage DC motor running at around 5V)
      • gears with an output shaft
      • position-sensing mechanism (usually potentiometer connected to output position)
      • control circuitry (usually special IC and some discrete components)

      The position-sensing mechanism tells the servo what position the shaft currently has. 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 555 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 1991 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. You can mix Futaba servos with an Airtronics receiver, mix Hitec & JR servos with a Futaba receiver, etc. 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 1-2ms with 1.5ms being the nominal centre period.

      Besides controlling only RC servo motors, those RC servo control pulses are used to control the RC device main running motor speeds. Those DC motors are controlled with a motor controller that have as input an R/C servo signal, and shall generate a modulated pulse whose width and polarity are proportional to width of that signal. For this kind of applications the Futaba timings define "neutral" or "no activation" to be 1522 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."

      There are some people that modify existing servo motors. You can't reverse the direction of a servo (reversed servo) by swapping (+) and (-). 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 4.8V battery or so). 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.

      Stepper motors

      Stepping motors can be viewed as electric motors without commutators. 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. The stepper's resolution is based on the steps (typically 1.8 deg or 3.6 deg per step). In the stepper system, the driver advances one step, and the stepper motor follows. For example a a 1.8 deg. stepper will turn a full circle in 200 steps. 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.

      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 1.8 or even 0.72 degrees per step. 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. Some of the top end (expensive) chopper controllers support 256 microsteps and even have error correction systems that are said to make 256 * 200 = 51,200 positions a reality!

      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 have a specified number of steps per revolution (typically around 200 steps/rev, or 1.8 degrees per step). 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. 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:

      • Single-Coil Excitation (Wave-drive): A-B-C-D sequence, least power used
      • Two-Coil Excitation (Two-phase drive): AB-BC-CD-DA sequence, more torque than Single-Coil Excitation
      • Interleaved Single- and Two-Coil Excitation (Half-step): A-AB-B-BC-C-CD-D-DA sequence, this runs the motors at half step resolution
      Stepper motors have their limitations. They are available in limited power (less than one horse power) and their rotation speed is limited (usually maximum speed limit is about 2000 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.

      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.

        Technical information

      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.m. motor which is driven as a generator and which gives an output voltage which is accurately calibrated to be a defined measure of the rotation speed. 'Accurate' implies expensive. 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. Sensors are available which give an output pulse whenever a metal object passes them, so these will give a train of pulses at a rate proportional to the rate of the gear teeth passing th sensor. These pulses have to be fed into a 'frequency to voltage converter' (FVC) which turns the pulse rate into a variable voltage which is used instead of the signal from the tacho generator.

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