Using a Servo

I've decided to see how much control I can add to the robot arm project so I bought a servo. This is a small motor that can be set to specific positions based on a signal. Such a device has 3 input lines, 2 for power and one for the signal.

First off, I wanted to use my new Ubuntu laptop to develop the Arduino code. Unfortunately, after installing the Arduino IDE and updating to version 1.6.7 I got the following error trying to upload the blink sketch:


avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied

This is because in Ubuntu the current user isn't automatically given permission to the usb device. To grant permission I followed these steps

1. whoami (get username)
2. sudo usermod -a -G dialout username : Modify user, add to dialout group (allows access to serial ports via files in /dev)
3. sudo chmod a+rw /dev/ttyACM0 : give '+' all users 'a' read/write 'rw' access to /dev/ttyACM
   

Now I was able to upload to the Ardunio I connected the servo, shown below

• Brown : Groud
• Red : + 5v
• Yellow : S(ignal)

One thing I noticed, I had the servo plugged into SERVO_2 on the motor shield, conecting to SER1 resulted in the controller chip rapidly heating. Fortunately no damage was done.

I tried using the Sweep sketch with this and then the following

#include <Servo.h>

Servo servo;
void setup() {
  // Attach the servo on pin 9 to the servo object
  servo.attach(9);
}

void loop() {
   servo.write(20);
   delay(1000);
 
   servo.write(160);
   delay(1000);
}    

A problem with this setup was the servo sometimes would jitter or stall. I suspect this was due to interference from the Arduniop and related perhaps to automation in the loop. I managed to reduce this almost entirely by removing the sleeps from the above sample and setting the angle via serial input:

#include <Servo.h>

Servo servo;
void setup() {
  // Attach the servo on pin 9 to the servo object
  servo.attach(9);
  Serial.begin(19200);
  Serial.println("Ready");
}

void loop() {

  if (Serial.available())
  {
    char ch = Serial.read();

    switch(ch)
    {     
      case '1':
        servo.write(40);
        break;
      case '2':
        servo.write(60);
        break;
      case '3':
        servo.write(80);
        break; 
      case '4':
        servo.write(100);
        break;     
      case '5':
        servo.write(120);
        break;              
    }
  }
}

I was also happy with this because I'll be controlling from the Raspberry Pi in a similar way to this in the future.