[Description]

- A crawler with a single servo motor

 - The boom pushes against the ground in one direction only.

[Components]

- Servo Motor

- Erector Kits

- Rubber Band

- Paper Tape

- Cardboard

[Arduino Code]

int servoPin = 7;      // Control pin for servo motor

int pulseWidth = 0;    // Amount to pulse the servo
long lastPulse = 0;    // the time in millisecs of the last pulse
int refreshTime = 20;  // the time in millisecs needed in between pulses
int val;               // variable used to store data from serial port

int minPulse = 500;   // minimum pulse width
int maxPulse = 2250;  // maximum pulse width

void setup() {
  pinMode(servoPin, OUTPUT);  // Set servo pin as an output pin
  pulseWidth = minPulse;      // Set the motor position to the minimum
  Serial.begin(9600);         // connect to the serial port
  Serial.println("Servo control program ready");
}

void loop() {
  val = Serial.read();      // read the serial port
  if (val >= '1' && val <= '9' ) {
    val = val - '0';        // convert val from character variable to number variable
    val = val - 1;          // make val go from 0-8
    pulseWidth = (val * (maxPulse-minPulse) / 8) + minPulse;  // convert val to microseconds
    Serial.print("Moving servo to position ");
    Serial.println(pulseWidth,DEC);
  }
  updateServo();   // update servo position
}

// called every loop().
// uses global variables servoPi, pulsewidth, lastPulse, & refreshTime
void updateServo() {
  // pulse the servo again if rhe refresh time (20 ms) have passed:
  if (millis() - lastPulse >= refreshTime) {
    digitalWrite(servoPin, HIGH);   // Turn the motor on
    delayMicroseconds(pulseWidth);  // Length of the pulse sets the motor position
    digitalWrite(servoPin, LOW);    // Turn the motor off
    lastPulse = millis();           // save the time of the last pulse
  }
}

[Video]