Project 21: Servo Control

Overview

Servo is a position control rotary actuator. It mainly consists of a housing, a circuit board, a core-less motor, a gear and a position sensor.

In general, servo has three lines in brown, red and orange. The brown wire is grounded, the red one is a positive pole line and the orange one is a signal line.

Working Principle

The rotation angle of servo motor is controlled by regulating the duty cycle of PWM (Pulse-Width Modulation) signal. The standard cycle of PWM signal is 20ms (50Hz). Theoretically, the width is distributed between 1ms-2ms, but in fact, it’s between 0.5ms-2.5ms. The width corresponds the rotation angle from 0° to 180°. But note that for different brand motors, the same signal may have different rotation angles.

Components

Connection Diagram

Test Code 1

//**********************************************************************
/*
 * Filename    : Servo_1
 * Description : Steering gear rotation Angle 0-90-180, repeatly
 * Auther      : http//www.keyestudio.com
*/
int servoPin = 4;//steering gear PIN

void setup() {
  pinMode(servoPin, OUTPUT);//steering pin is set to output
}
void loop() {
  servopulse(servoPin, 0);//Rotate it to zero degrees
  delay(1000);//delay 1S
  servopulse(servoPin, 90);//Rotate it to 90 degrees
  delay(1000);
  servopulse(servoPin, 180);//Rotate it to 180 degrees
  delay(1000);
}

void servopulse(int pin, int myangle) { //Impulse function
  int pulsewidth = map(myangle, 0, 180, 500, 2500); //Map Angle to pulse width
  for (int i = 0; i < 10; i++) { //Output a few more pulses
    digitalWrite(pin, HIGH);//Set the steering gear interface level to high
    delayMicroseconds(pulsewidth);//The number of microseconds of delayed pulse width value
    digitalWrite(pin, LOW);//Lower the level of steering gear interface
    delay(20 - pulsewidth / 1000);
  }
}
//**********************************************************************

Code Explanation 1

1. map(value, fromLow, fromHigh, toLow, toHigh)；Value is the value we map. fromLow, fromHigh is the maximum and minimum value；

toLow, toHigh are the upper limit and lower limit we map. For example, map(myangle, 0, 180, 500, 2500) means that an angle value myangle(0°-180°）the mapping range is from 500us to 2500us.

We use the function servopulse() to make the servo move. We also make the servo rotate 0°, 90°and 180°cyclically.

Test Result 1

Connect the wires according to the experimental wiring diagram, compile and upload the code to the ESP32. After uploading successfully，we will use a USB cable to power on, the servo will rotate 0°，90° and 180° cyclically.

Test Code 2

//**********************************************************************
/*
 * Filename    : Servo Sweep
 * Description : Control the servo motor for sweeping
 * Auther      : http//www.keyestudio.com
*/
#include <ESP32Servo.h>

Servo myservo;  // create servo object to control a servo

int posVal = 0;    // variable to store the servo position
int servoPin = 4; // Servo motor pin

void setup() {
  myservo.setPeriodHertz(50);           // standard 50 hz servo
  myservo.attach(servoPin, 500, 2500);  // attaches the servo on servoPin to the servo object
}
void loop() {

  for (posVal = 0; posVal <= 180; posVal += 1) { // goes from 0 degrees to 180 degrees
    // in steps of 1 degree
    myservo.write(posVal);       // tell servo to go to position in variable 'pos'
    delay(15);                   // waits 15ms for the servo to reach the position
  }
  for (posVal = 180; posVal >= 0; posVal -= 1) { // goes from 180 degrees to 0 degrees
    myservo.write(posVal);       // tell servo to go to position in variable 'pos'
    delay(15);                   // waits 15ms for the servo to reach the position
  }
}
//********************************************************************************

Code Explanation 2

myservo. write (pos) is the rotation angle to POS.  myservo. read () reads the current angle value of the servo.

Test Result 2

Connect the wires according to the experimental wiring diagram, compile and upload the code to the ESP32. After uploading successfully，we will use a USB cable to power on, the servo will rotate from 0° to 180° by moving 1° for each 15ms.