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Servo

Table of Contents

  1. Hello World!
  2. Library
  3. Details
  4. Examples

A library for controlling a Radio Control (R/C) model Servo.

R/C Model Servo

Hello World!

main.cpp

// Sweep the servo through its full range

#include "mbed.h"
#include "Servo.h"

Servo myservo(p21);

int main() {    
    while(1) {
        for(float p=0; p<1.0; p += 0.1) {
            myservo = p;
            wait(0.2);
        }
    }
}

Library

This library controls a standard R/C model servo using a PwmOut signal, and provides control of the servo between min and max by setting it to 0.0 - 1.0.

As all servos respond differently, you can also use the calibrate function the range, so 0.0 - 1.0 is the maximum range of the servo.

Details

The underlying PwmOut period is set to 20ms, and by varying the pulsewidth (up to a maximum of 0.5ms to 2.5ms) the position of the servo is changed, usually by around 180 degrees. The library lets you calibrate the exact range.

The servo must connect to a PwmOut, and be supplied with a separate power supply, usually in the range 4.5-6.0v.

Warning

A servo requires higher current than the USB port can safely provide, and so it is essential that you power the servo using an external supply, such as a 4xAA (6v) battery pack or an appropriate DC power adaptor.

/media/uploads/simon/servoschematic.png /media/uploads/simon/servophoto.jpg

Examples

Calibrate a Servo

#include "mbed.h"
#include "Servo.h"

Servo myservo(p21);
Serial pc(USBTX, USBRX);

int main() {
    printf("Servo Calibration Controls:\n");
    printf("1,2,3 - Position Servo (full left, middle, full right)\n");
    printf("4,5 - Decrease or Increase range\n");

    float range = 0.0005;
    float position = 0.5;
    
    while(1) {                   
        switch(pc.getc()) {
            case '1': position = 0.0; break;
            case '2': position = 0.5; break;
            case '3': position = 1.0; break;
            case '4': range += 0.0001; break; 
            case '5': range -= 0.0001; break; 
        }
        printf("position = %.1f, range = +/-%0.4f\n", position, range);
        myservo.calibrate(range, 45.0); 
        myservo = position;
    }
}

/users/simon/programs/ServoProgram

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