A servomotor is a motor capable to stay in a position given by the user. A servomotor can’t exceed a position of 180°. According to the servomotor you have choosen, you can have a tork important to stay at the position choosen.
All theses features make this motor a useful component to open a door, open a valve or the direction of the car.
Nevertheless if you want to spin a propeller or to use the motor as a dynamo, you will need a motor dc.
If you want a motor which keep the position and turn at 360 degrees, you can use a stepper motor.
In this course we will see how to control your servomotor by two ways: a program which turn the servomotor from 0° to 180° and go back to the initial position and a program to control the servomotor by yourself with the serial monitor.
A servomotor is composed of different elements:
The servomotor is controlled with pulse width modulation (pwm) with a fixed frequency of 50 hz (T=20 ms) and the high state of the signal determines the position of the servomotor.
That’s mean that the duration of the pulse determinates the absolut angles therefore the position of the servomotor.
This signal is repeated periodically, in general every 20 milliseconds, which permits at the card to control and correct the continuously the position. This one is measured by the potentiometer.
The servomotor works with three wires:
Nevertheless if you need a servomotor with a torque more important, you can choose 35kg servomotors.
The servomotor works with a library which help you to control it. You can download the library and read our course about the libraries to install it.
In this part we will see how to turn your servomotor from 0° to 180° and back to the initial position.
#include <Servo.h>
Servo myServomotor; // On create an object servomotor
int pos = 0; // variable to store the position
void setup() {
myServomotor.attach(9); // We attach the servomotor to the pin 9. On attache le servomoteur a la broche 9
}
void loop() {
for (pos = 0; pos <= 180; pos += 1) { // Loop from 0 to 180 degrees
myServomotor.write(pos); // We give the position to the servomotor
delay(15); // We make a break of 15 millisecondes
}
for (pos = 180; pos >= 0; pos -= 1) { // Loop from 180 to 0 degrees
myServomotor.write(pos); // We give the position to the servomotor
delay(15); // We make a break of 15 millisecondes
}
}
This is the program to control the servomotor with the serial monitor. The circuit remains the same.
#include <Servo.h>
Servo myServomotor;
int position_question;
void setup(){
Serial.begin(9600);
myServomotor.attach(9);
Serial.println("-------------------------");
Serial.println(" Give the position of the servomotor between 0 and 180 degrees :");
}
void loop() {
if (Serial.available()) {
Serial.println("-------------------------");
Serial.print(" Give the position of the servomotor between 0 and 180 degrees :");
position_question = Serial.parseInt();
Serial.println(position_question);
}
if (position_question < 0) {
Serial.println(" The value is lower than 0, therefore 0 will be taken");
position_question=0;
}
if (position_question > 180) {
Serial.println(" The value is higher than 180, therefore 180 will be taken");
position_question=180;
}
myServomotor.write(position_question);
}
#include <Servo.h>
int Potentiometer; // Variable for the potentiometer
int Conversion;
Servo myServomotor; // We creat an object servomotor
void setup() {
myServomotor.attach(9); // We attach the servomotor to the pin 9
}
void loop() {
Potentiometer = analogRead(A0); // We read the value from the potentiometer
Conversion=map(Potentiometer,0,1023,180,0); // We convert this value to range from 0° to 180°
myServomotor.write(Conversion); // We give the position to the servomotor
}
The servomotor works with a library which will simplify its use.
In this part we will show the different functions contains in the library if you want to directly include it in your program.
attach(pin) : Function to associate the servomotor to the pin of the Arduino card which is plugged in.
Here is the program corresponding to attach(pin) function:
uint8_t Servo::attach(int pin, int min, int max)
{
if(this->servoIndex < MAX_SERVOS ) { // If the number of servomotor is lower than the maximum of servomotor that we can controled (12)
pinMode( pin, OUTPUT) ; // We associate the servomotor to the output pin
servos[this->servoIndex].Pin.nbr = pin;
this->min = (MIN_PULSE_WIDTH - min)/4; // We define the minimum position of the servomotor
this->max = (MAX_PULSE_WIDTH - max)/4; // We define the maximum position of the servomotor
// On initialise le timer
timer16_Sequence_t timer = SERVO_INDEX_TO_TIMER(servoIndex);
if(isTimerActive(timer) == false)
initISR(timer);
servos[this->servoIndex].Pin.isActive = true; // We activate the pin after the timer
}
return this->servoIndex ;
}
Here is the program corresponding to the function write(angle) in the library:
void Servo::write(int value) {
if(value < MIN_PULSE_WIDTH) {
if(value < 0) value = 0; //If the value is lower than 0 degree, we assign 0 to value
if(value > 180) value = 180; // If the value is higher to 180 degres, we assign 180 to the value
value = map(value, 0, 180, SERVO_MIN(), SERVO_MAX());
}
this->writeMicroseconds(value); // We write the value with the function writeMicroseconds.
}int Servo::read() // return the actual position of the servomotor
{
return map( this->readMicroseconds()+1, SERVO_MIN(), SERVO_MAX(), 0, 180);
}
Here is the program corresponding to the writeMicroseconds function in the library:
bool Servo::attached() // Return the associated pin at the servomotor
return servos[this->servoIndex].Pin.isActive ;
}This program correspond to the function writeMicroseconds in the library:
void Servo::writeMicroseconds(int value){
// This funciton is used to create the link between the servomotor and the program
byte channel = this->servoIndex;
if( (channel < MAX_SERVOS) ) // ensure channel is valid
{
if( value < SERVO_MIN() ) // We verify if the values are correct
value = SERVO_MIN();
else if( value > SERVO_MAX() )
value = SERVO_MAX();
value = value - TRIM_DURATION;
value = usToTicks(value);
uint8_t oldSREG = SREG;
cli();
servos[channel].ticks = value;
SREG = oldSREG;
}
}You can also control a servomotor with python. We have made a course about it to help you.