DC Motor

DC Motor are electromechanical devices that use the interaction of magnetic fields and conductors to convert electrical energy into mechanical energy.

DC Motors are continuous actuators that convert electrical energy into mechanical energy.The DC motor achieves this by producing a continuous angular rotation that can be used to rotate pumps, fans, compressors, wheels, etc.

In addition to conventional rotary DC motors, linear motors are also available that can produce continuous primer movement.Basically, there are three types of conventional electric motors: AC type Motors, DC type Motors and StepPer Motors.

DC Motor
DC Motor

AC Motors are often used in high-power single or multi-phase industrial applications where a constant rotational torque and speed are required to control large loads such as fans or pumps.

In this tutorial on electric motors, we will look only at DC Motors and StepPer Motors, which are for simple light work used in many different electronic, positional control, microprocessor, PIC and robotic type circuits.

Basic DC Motor

The DC Motor or direct current motor is the most commonly used actuator for producing continuous motion, and the rotational speed can be easily controlled, making it ideal for use in applications requiring speed control, servo type control and/or positioning. A DC motor consists of two parts: a "Stator" with a fixed part and a Rotor with a rotating part. As a result, there are basically three types of DC Motors.

  • Brushed Motor – This type of engine produces a magnetic field in a winding rotor (rotating part) by passing an electric current through a commune and carbon brush assembly, hence the term "Brushed".The magnetic field of stators (fixed part) is produced using either a stator field winding or permanent magnets.Usually brushed DC motors are inexpensive, small and easily controlled.
  • Brushless Motor – This type of motor produces a magnetic field in the rotor using permanent magnets attached to it and electronic commutation is provided.They are usually smaller because they use "Hall effect" switches in the stator to produce the required stator area rotation sequence, but they are more expensive than conventional brushed type DC motors, but they have better torque/speed characteristics, are more efficient than equivalent brushed species and have a longer working life.
  • Servo Motor – This type of motor is a brushed DC motor with a type of positional feedback control mainly connected to the rotor shaft.They are connected and controlled to a PWM type controller and are mainly used in positional control systems and radio-controlled models.

Normal DC motors have almost linear properties with rotational speeds determined by the dc voltage applied and output torques determined by the current flowing from the motor windings.The rotational speed of any DC engine can vary from a few revolutions per minute (rpm) to thousands of revolutions per minute, making them suitable for electronic, automotive or robotic applications.By connecting them to gearboxes or gearboxes, output speeds can be reduced while at the same time increase the engine's torque output at high speed.

Brushed DC Motor

A conventional brushed DC Motor consists mainly of two parts, the fixed body of the engine called Stator and the rotating interior, which produces the movement called Rotor or "Fixture" for DC machines.

Unlike AC machines, the motor-winded stator is an electromagnet circuit consisting of electrical coils connected together in a circular configuration to produce the necessary north pole, followed by the south pole, and then the north pole, etc. The Stator field rotates continuously with the applied frequency.The current flowing through these area coils is known as the motor field current.

These electromagnetic coils that make up the stator field can be electrically connected with the motor armature in series, parallel or both (compounds).A series of winding DC motors have stator field windings connected serially with the fixture.Similarly, the stator field windings of a DC motor with shunt winding are connected in parallel with the fixture, as shown in the way.

Serial and Shunt Connected DC Motor

DC Motor

The rotor or fixture of a DC machine consists of current-bearing conductors connected to electrically insulated copper segments called commutators at one end.The commute allows electrical connection to an external power source via carbon brushes (hence the "Brushed" engine name) as the fixture rotates.

The magnetic field established by the rotor tries to align itself with the fixed stator field, which causes the rotor to rotate on its axis, but cannot align itself due to commutation delays.The rotational speed of the engine depends on the power of the rotors' magnetic field, and the more voltage is applied to the motor, the faster the rotor rotates.The rotation speed of the motor can also be changed by changing this DC voltage applied.

Conventional (Brushed) DC Motor

DC Motor
Brushed Motor

The DC motor with permanent magnet (PMDC) brush is usually much smaller and cheaper than equivalent winding stator type DC motors because there is no field winding.In fixed magnet DC (PMDC) motors, these field coils are replaced by powerful rare earth (i.e. Samarium Cobolt or Neodymium Iron Boron) type magnets with very high magnetic energy fields.

The use of permanent magnets gives the DC motor a much better linear speed/torque feature than equivalent winding motors due to its permanent and sometimes very strong magnetic field, making them more suitable for use in models, robots and servos.

Although DC brushed motors are very efficient and inexpensive, problems with the brushed DC motor are that the commute creates sparks between the two surfaces and carbon brushes under heavy load conditions, resulting in self-generating heat generation, short life and electrical noise due to sparking. It can damage any semiconductor switching device, such as a MOSFET or transistor.Brushless DC Motors have been developed to overcome these disadvantages.

Brushless DC Motor

The brushless DC motor (BDCM) is very similar to a DC motor with a fixed magnet, but it does not have any brushes to replace or erode due to the commute spark.Therefore, very little heat is generated in the rotor and extends the engine life.The design of the brushless motor eliminates the need for brushes using a more complex drive circuit; Since the rotor magnetic field is a permanent magnet that always syncs with the stator field, it provides more precise speed and torque control.

Then the structure of a brushless DC motor is very similar to the AC motor, making it a real synchronous engine, but one drawback is that it is more expensive than an equivalent "brushed" engine design.

Control of brushless DC motors is very different from the normal brushed DC motor, since this type of motor includes some tools to detect the angular position (or magnetic poles) of the rotors needed to produce the feedback signals needed to control semiconductor switching.The most common position/pole sensor is the "Hall Effect Sensor", but some engines also use optical sensors.

Using Hall effect sensors, the polarity of electromagnets is changed by the motor control drive circuit.The engine can then be easily synchronized to a digital watch signal, providing precise speed control.Brushless DC motors can be made to have an external fixed magnet rotora and a built-in electromagnet stator or a built-in fixed magnet rotor and an external electromagnet stator.

Brushless DC Motor Its advantages over the "brushed" engine are higher efficiency, high reliability, low electrical noise, good speed control and, more importantly, the absence of brushes or commuters to erode, producing a much higher speed.But the disadvantages are that they are more expensive and more complicated to control.

DC Servo Motor

DC Servo motors areused in closed cycle type applications where the position of the output motor shaft is fed back into the engine control circuit.Typical positional "Feedback" devices include Analyzers, Encoders, and Ponsiometers used in radio control models such as airplanes and boats.

A servo motor usually includes a built-in gearbox for de-speeding and can transmit high torques directly.Due to the output shaft of a servo motor, the connected gearbox and feedback devices, dc motors do not rotate as freely as shafts.

DC Servo Motor Block Diagram

DC Motor

A servo motor consists of a DC motor, a reduction gearbox, a positional feedback device and some kind of bug correction.The speed or position is controlled according to a positional input signal or reference signal applied to the device.

DC Motor
Servo Motor

The error detection amplifier looks at this input signal and compares it to the feedback signal from the engine output shaft and determines whether the engine output shaft is in an error state, and if so, the controller makes the appropriate corrections by accelerating or slowing down the engine. down.This response to the positional feedback device means that the servo motor operates in a "Closed Loop System".

Servo motors are used in small remote control models and robots, as well as large industrial applications; most servo motors can rotate up to about 180 degrees in both directions, making them ideal for accurate angular positioning.However, these RC-type servos, unless specifically modified, cannot constantly turn at high speed, like traditional DC motors.

A servo motor consists of several devices in a single package; engine, gearbox, feedback device and error correction circuit to control location, direction or speed. They are widely used in robotics and small models as they can be easily controlled using only three cables: Power, Soil and Signal Control.

DC Motor Switching and Control

Small DC motors can be made "On" or "Off" through switches, relays, transistors or MOSFET circuits, and the simplest form of engine control is "Linear" control.This type of circuit uses a bipolar Transistor as the Switch to control the motor from a single power source (a Darlington transistor can also be used if a higher degree of current is required).

The speed of the motor can be controlled by changing the amount of basic current flowing into the transistor, for example, if the transistor is turned on "halfway", only half of the supply voltage goes to the motor.If the transistor is made "fully ON" (saturated), the entire supply voltage goes to the motor and rotates faster.Then, for this type of linear control, power is continuously transmitted to the engine, as shown below.

Engine Speed Control

DC Motor

The simple switching circuit above shows a one-way (one-way only) engine speed control circuit.Since the rotational speed of a DC motor is proportional to the voltage in its terminals, we can regulate this terminal voltage using a transistor.

Optional flywheel diodes are connected along the switching transistor, TR 2 and engine terminals for protection against any back emf produced by the engine while rotating.The adjustable ponciometer can be replaced by a continuous logic "1" or logic "0" signal applied directly to the input of the circuit to switch the motor "completely ON" (saturation) or "completely OFF" (cut) from the port of a microcontroller or PIC, respectively.

In addition to this basic speed control, the same circuit can also be used to control the rotational speed of the engines.By repeatedly changing the engine current to "ON" and "OFF" at a sufficiently high frequency, the speed of the motor can be changed between immobile (0 rpm) and full speed (100%) by changing the signal-to-gap ratio.This is achieved by changing the ratio of "ON" time (t ON) to "OFF" time (t OFF), which can be achieved using a process known as Pulse Width Modulation.

Pulse Width Speed Control

We said that the rotational speed of a DC motor is directly proportional to the average voltage value in its terminals, and the higher this value is up to the maximum allowed engine voltage, the faster the engine will rotate.In other words, more voltage, more speed.By changing the ratio between the "ON" (t ON) duration and the "OFF" time periods, called "Duty Ratio", "Mark/Space Ratio" or "Duty Cycle", the engine voltage and therefore the rotation speed can be changed.Here's how the task rate β for simple unipolar drives:

DC Motor

and the average DC output voltage fed into the motor is given as follows: Vortalama = β x Vbesleme.Then, the width of the a pulse can be changed to control the engine voltage and therefore the power applied to the motor, and this type of control is called Pulse Width Modulation or PWM.

Another way to control the rotational speed of the engine is to change the frequency (and therefore the time period of the control voltage) while the "ON" and "OFF" duty rate times are kept constant.This type of control is called Pulse Frequency Modulation or PFM.

With pulse frequency modulation, motor voltage is controlled by applying variable frequency pulses, for example at low frequency or with very little impact, the average voltage applied to the motor is low and therefore the engine speed is slow.At a higher frequency or many pulses, the average motor terminal voltage increases and the engine speed also increases.

Next, Transistors can be used to control the amount of power applied to a DC motor whose operating mode is "Linear" (changing engine voltage), "Pulse Width Modulation" (varies according to the width of the pulse) or "Pulse Frequency". Modulation" (by changing the frequency of the pulse).

Reverse the Direction of the DC Motor

Although there are many advantages to controlling the speed of a DC motor with a single transistor, there is also one main drawback, the direction of rotation is always the same, it is a "One-way" circuit.In many applications we need to start the engine back and forth in both directions.

To control the direction of a DC motor, the polarity of the DC power applied to the connections of the motor must be reversed to allow the spindle to rotate in the opposite direction.A very simple and inexpensive way to control the direction of rotation of a DC motor is to use different switches arranged as follows:

DC Motor Direction Control

DC Motor

The first circuit uses a single bipolar, double-shot (DPDT) switch to control the polarity of the engine connections.By replacing the contacts, the supply to the motor terminals is reversed and the motor changes direction.The second circuit is a little more complex and uses four single-pole, single-shot (SPST) switches arranged in the "H" configuration.

Mechanical switches are arranged in switching pairs and must be operated in a specific combination to start or stop the DC motor.For example, the A+D switch combination controls forward rotation, while the B+C switches control the return as shown.Switch combinations A + B or C + D short-circuit the engine terminals, causing them to brake quickly.However, there are dangers to using the switches in this way, since running the A + C or B + D switches together shorts the power supply.

Although the above two circuits work very well for most small DC engine applications, do we really really only want to run different mechanical key combinations to reverse the direction of the engine ? Of course not.We can change the manual switches for the electromechanical relay set and have a single back-and-forth button or switch, or even use a solid state CMOS 4066B quad dual switch.

But another very good way to maintain two-way control of an engine (and its speed) is to connect the motor to a Transistor H-bridge type circuit arrangement, as shown below.

Basic Duplex H-bridge Circuit

DC Motor

The above H-bridge circuit is named because the basic configuration of the four switches, electro-mechanical relays or transistors, resembles the letter "H" with the motor placed on the middle bar. The transistor or MOSFET H-Bridge is probably one of the most commonly used duplex DC motor control circuits. Both NPN and PNP use "complementary transistor pairs" in each branch, and transistors are replaced together in pairs to control the motor.

Control input A starts the engine in one direction, that is, on the forward turn, while input B starts the motor in the other direction, that is, on the turn.Then, in the "diagonal pairs" of transistors, "ON" or "OFF" provides directional control of the engine.

For example, when transistor TR1 is "on" and transistor TR2 is "off", point A is connected to the supply voltage (+Vcc), and if transistor TR3 is off "and transistor TR4" is on, point B is connected to 0 volts (GND). The engine will then rotate in a direction corresponding to the positive of engine terminal A and negative of engine terminal B.

If the switching states are reversed to TR1 "off", TR2 "on", TR3 "on" and TR4 "off", the engine current will now flow in the opposite direction, causing the motor to rotate in the opposite direction.

Then, the rotation direction of the engines can be controlled as follows by applying opposite logic levels "1" or "0" to inputs A and B.

H-bridge Accuracy Table

A entryInput BMotor Function
TR1 and TR4TR2 and TR3 
00Engine Stopped (OFF)
10Engine Spins Forward
01Engine Reverses
11Not recommended

It is important that no other input combinations are allowed, since this can cause the power supply to short-circuit, that is, both transistors, TR1 and TR2 are turned on at the same time, which leads to an fuse explosion, if any, or disruption-commvation of other components in the circuit.

As with the one-way DC engine control as seen above, the rotational speed of the engine can be controlled using Pulse Width Modulation or PWM.Then, by combining H-bridge switching with PWM control, both the direction and speed of the engine can be accurately controlled.

Commercially ready-to-use decoder IC's, such as the SN754410 Quad Half H-Bridge IC or L298N with 2 H-Bridges, are available with all the necessary control and built-in safety logic, specially designed for H-bridge duplex engine control circuits.

DC Step Motor

Like the DC motor above, Step Motors are electromechanical actuators that convert a pulsed digital input signal into a discrete (incremental) mechanical motion, widely used in industrial control applications.Stepper motor is a type of synchronous brushless motor in which it does not have an armature with a commune and carbon brush, but consists of many rotors, some types have hundreds of permanent magnetic teeth and a statora with separate bandages.

DC Motor

As its name suggests, the stepper motor does not rotate continuously like a traditional DC motor, but the angle of each rotational movement or step moves in separate "Steps" or "Increments", depending on the number of stator poles and rotors.

Stepper motors, due to their separate step operation, can be rotated as easily as a finous fraction of a rotation such as 1.8, 3.6, 7.5 degrees, etc. at a time. For example, suppose a stepper engine completes a full rotation (360 o) in exactly 100 steps.

Then the step angle for the motor is given as 360 degrees/100 steps = 3.6 degrees per step.This value is often known as stepper angle of stepper motors.

DC Motor
StepPer Inside the Engine

There are three basic types of stepper motors, Variable Relux , Permanent Magnet and Hybrid (a kind of combination of the two).A Step Motor is particularly suitable for applications that require accurate positioning and repeatability with quick response to start, stop, reverse and speed control, and another important feature of the stepper motor is its ability to hold the load steady once the required position is determined. That's why it's used in 3D printers.

In general, stepper motors have a built-in rotor containing a large number of permanent magnet "teeth" with a series of electromagnet "teeth" mounted on the stator.Stator electromagnets are polarized and stored in turn, causing the rotor to rotate one "step" at a time.

Modern multipolar, multi-gear stepper motors have a accuracy capacity of less than 0.9 degrees per step (400 Pulses Per Revolution) and are mainly used for highly precise positioning systems, such as those used for magnetic heads on floppy disk/hard disk drives. printers/plotters or robotic applications.The most commonly used stepper motor is the 200-step stepper motor per revolution.The 50-tooth rotor has a 4-phase stator and a step angle of 1.8 degrees (360 degrees/(50×4)).

StepPer Motor Structure and Control

DC Motor

In our simple example of the variable reluxed stepper motor above, the motor consists of a central rotor surrounded by four electromagnetic field coils labeled A, B, C and D.All coils with the same letter are connected to each other, so that energizing, for example, coils marked with an A cause the magnetic rotor to align itself with this set of coils.

By applying power to each group of coils respectively, the rotor can be rotated or "stepped" from one position to another at an angle determined by the step angle structure, and by giving the coils energy in turn, the rotor will produce a rotating rotation.

The gradual motor drive, for example " ADCB, ADCB, ADCB, A… " control both the step angle and speed of the motor by energizing the field coils in a certain order, such as " and the rotor rotates in one direction (forward) and the pulse sequence " ABCD, ABCD, ABCD, A… " etc. and the rotor will rotate in the opposite direction.

In our simple example above, the stepper motor has four coils, which makes it a 4-phase engine, and the number of poles on the stator is eight (2 x 4), placed at 45 degree intervals.The number of teeth on the rotor is six with a 60 degree interval.

Then there are 24 (6 threads x 4 coils) possible position or "step" for the rotor to complete a full turn.Therefore, the above step angle is 360 o /24 = 15 o.

Obviously, more rotor teeth and/or stator coils will result in more control and a finer step angle.In addition, full, half and micro step angles are possible by connecting the electric coils of the motor in different configurations.However, in order to achieve micro-step, the step motor must be operated with a (semi) sinusoidal current, which is expensive to apply.

It is also possible to control the rotational speed of a stepper motor by changing the time delay between digital pulses (frequency) applied to the coils, the slower the speed for a full speed, the longer the delay.By applying a fixed number of pulses to the motor, the engine shaft will rotate at a certain angle.

The advantage of using time-delayed pulse is that no additional forms of feedback are required, as the final position of the rotor will be fully known, counting the number of blows to the engine.This response to a certain number of digital input pulses allows the stepper motor to operate in an "Open Loop System", making control both easier and cheaper.

For example, let's say that our stepper engine above has a step angle of 3.6 degrees per step.To rotate the engine at an angle of 216 degrees, for example, and then stop it again in the required position, only a total of: 216 degrees/(3.6 degrees/step) = 80 strokes applied to stator coils are required.

There are many stepper engine control IC's that can control step speed, rotational speed and engine direction.Such controller IC is the SAA1027, which has all the necessary counter and decoding built-ins and can automatically route 4 fully controlled bridge outputs to the engine in the correct order.

The rotation direction can also be selected along with a single step mode or continuous (stepless) rotation in the selected direction, but this brings some load to the controller.When using an 8-bit digital controller, 256 micro-steps per step are also possible

SAA1027 StepPer Motor Control Chip

DC Motor

In this tutorial on Rotary Actuators, we examined the brushed and brushless DC Motor, DC Servo Motor and StepPer Motor as an electromechanical actuator that can be used as an output device for positional or speed control.