Definition
A direct current or DC motor, converts electrical energy into mechanical energy. It is one of two basic types of motors: the other type is the alternating current or AC motor. Among DC motors, there are shunt-wound, series-wound, compound-wound and permanent magnet motors.
Function
A DC motor consists of an stator, an armature, a rotor and a commutator with brushes. Opposite polarity between the two magnetic fields inside the motor cause it to turn. DC motors are the simplest type of motor and are used in household appliances, such as electric razors, and in electric windows in cars.
DC MOTOR WORKING PRINCIPLE
The DC motor working principle is that a current-carrying conductor experiences a mechanical force when placed in a magnetic field. This is known as the Lorentz force. And the direction of this force is given by FLEMING’S LEFT-HAND RULE.
DC motor working principle is similar to the working principle of a DC generator.
Magnitude is F=B.I.L
Where,
B = magnetic flux density,
I = current and
L = length of the conductor within the magnetic field.
FLEMING’S LEFT-HAND RULE
It states that “If we stretch the first finger, second finger and thumb of our left hand to be perpendicular to each other, and the direction of magnetic field is represented by the first finger, direction of the current is represented by the second finger, then the thumb represents direction of the force experienced by the current carrying conductor.”
CONSTRUCTION OF DC MOTOR
All DC machines mainly consist of two parts. One is the stator and the other is Rotor. The stator is a stationary part that includes yoke, pole, pole winding, and Interpoles. The stator produces the magnetic flux.
The rotor of the dc machine consists of a commutator, brushes, compensating winding, and a shaft. It rotates in external magnetic flux(produces by the stator) when the current flows in it.
PARTS OF DC MOTOR
PARTS OF THE STATOR:-
YOKE:
The yoke or outer frame provides coverage to a dc motor. It is made up of cast steel for large dc motors. And of cast iron for small dc motors. The yoke is used in DC machine because:
A) It provides mechanical support to poles.
B) Acts as a protective cover against mechanical damage.
C) And provides a passage for the magnetic flux produced by the poles of the machine.
POLE CORE AND POLE SHOE:
Both pole core and pole shoes are made of cast steel. But pole shoes are laminated as they are close to the armature.
If the load changes during the operation of the DC motor, the armature current changes. As a result the magnetic flux also changes. This flux links the pole shoe and causes eddy current to flow. And to minimize these eddy currents, pole shoes are laminated.
The main purpose of the pole shoe is to spread the flux and reduce the reluctance of the magnetic path. Whereas the pole core is excited with field winding and used to support them.
POLE WINDING OR FIELD COILS
The pole winding and field coils consist of copper wire placed in position around the pole core. When current passes through these coils, they electro-magnetize the pole which produces the magnetic flux. This flux passes through the rotor and produces a rotating torque as soon as the current starts flowing in the armature of the rotor.
PARTS OF THE ROTOR:-
ARMATURE CORE
The armature core is the rotating part of a DC/AC machine. It is made up of silicon steel. The cylindrical structure is laminated to reduce the eddy current loss. Its main purpose is to offer a low reluctance path to the magnetic flux. And to house the armature conductors.
ARMATURE WINDING
Armature winding is composed of coils embedded in armature core slots. These coils are lined next to each other with tough insulating material. The insulating material prevents the two adjacent coils from a short circuit.
Whereas the slot insulation is folded over the armature conductor and is secured firmly by wood or Fibre wedges. In simple words, it is an arrangement of current-carrying conductors that produce EMF in the machine due to relative motion between the windings and the main field.
COMMUTATOR
The commutator contains wedge-shaped hard drawn copper segments, forming a cylindrical structure. A thin sheet of high-quality mica insulates the segments from each other.
A commutator periodically changes the direction of the current between the rotor and external circuit. Hence, it acts as a switch causing a unidirectional torque in the dc motor.
BRUSHES
Brushes are usually made of rectangular carbon blocks housed in brush holders. The function of brushes in DC motors is to supply the current to the commutator from an external dc source.
Whereas the function of the brushes in a DC generator is to collect the current from the commutator and supply it to the external load circuit.
WORKING OF DC MOTOR
The working principle of DC motor requires magnetic flux and a current-carrying conductor. Consider a coil carrying DC current through commutator and brushes. These commutator segments rotate freely about its axis.
The commutator segment which comes in contact with the left brush gets positive polarity while the right one gets negative polarity. This leads to the flow of current in the coil.
By applying Fleming’s Left-Hand Rule, the conductor on the left side always experiences a force in an upward direction while the conductor on the right side experiences a downward force. Hence, a unidirectional torque is achieved in dc motors.
H-Bridge(Motor Driver)
An H bridge is an electronic circuit that enables a voltage to be applied across a load in either direction.
The L298 can control the speed and direction of DC motors and stepper motors and can control two motors simultaneously.
L293D is a dual H-bridge motor driver act as current amplifiers since they take a low-current control signal and provide a higher-current signal. This higher current signal is used to drive the motors.
L293D
L298 Pinout
L293D Operation
The motor operations of two motors can be controlled by input logic at pins 2 & 7 and 10 and 15.
Input logic 00 or 11 - stop the corresponding motor.
Logic 01 and 10 - rotate it in clockwise and anticlockwise directions, respectively
DC Motor Interfacing With Arduino
Do not drive the motor directly from Arduino board pins. This may damage the board. Use a driver Circuit or an IC.
Features of Arduino DC motor
· Standard 130 type Dc motor
· Operating voltage: 4.5V to 9V
· Recommended Voltage: 6V
· Current at No-load: 70mA (maximum)
· No-load speed: 9000 rpm
· Loaded current: 250mA (approximate)
· Rated Load: 10g*cm
DC Motor Using Potentiometer and Transistor
Circuit Diagram :
CODE :
void setup()
{
pinMode(3, OUTPUT);
Serial.begin(9600);
}
void loop()
{
for(int i=0; i<=255; i=i+50)
{
analogWrite(3, i);
Serial.println(i);
delay(2000);
}
for(int i=255; i>=0; i=i-50)
{
analogWrite(3, i);
Serial.println(i);
delay(2000);
}
delay(10);
}Result:
Motor will start rotating at a particular rpm when connected to circuit.
DC Motor Control Using Ultrasonic Sensor
Circuit Diagram:
CODE :
const int pingPin = A5;
void setup()
{
// initialize serial communication:
Serial.begin(9600);
pinMode(3,OUTPUT);
}
void loop()
{
long duration, inches, cm;
// The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
pinMode(pingPin, OUTPUT);
digitalWrite(pingPin, LOW);
delayMicroseconds(2);
digitalWrite(pingPin, HIGH);
delayMicroseconds(5);
digitalWrite(pingPin, LOW);
// The same pin is used to read the signal from the PING))): a HIGH pulse
// whose duration is the time (in microseconds) from the sending of the ping
// to the reception of its echo off of an object.
pinMode(pingPin, INPUT);
duration = pulseIn(pingPin, HIGH);
// convert the time into a distance
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm");
Serial.println();
if (inches <= 35)
{
digitalWrite(3,HIGH);
}
else if(inches >= 40){
digitalWrite (3,LOW);
}
delay(100);
}
long microsecondsToInches(long microseconds) {
// According to Parallax's datasheet for the PING))), there are 73.746
// microseconds per inch (i.e. sound travels at 1130 feet per second).
// This gives the distance travelled by the ping, outbound and return,
// so we divide by 2 to get the distance of the obstacle.
}
long microsecondsToCentimeters(long microseconds) {
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the object we
// take half of the distance travelled.
return microseconds / 29 / 2;
}
RESULT:
Motor will start work when object gets close to the ultrasonic sensor and motor will stop when distance is very large.
Check out the session on our youtube:
Written By: Sarthak
3rd year EEE
University Institute of Engineering and Technology, Panjab University
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