#include <Servo.h>

Servo Left;
Servo Right;
int echo = 2;
int trigger = 3;
long distance;
long duration;

void setup(){

  Serial.begin(9600);
  Left.attach(12);
  Right.attach(13);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
}

void moveForward(int time)
{
  Left.writeMicroseconds(1700);
  Right.writeMicroseconds(1300);
  delay(time);
}

void moveLeft(int time)
{
  Left.writeMicroseconds(1300);
  Right.writeMicroseconds(1300);
  delay(time);
}

void moveRight(int time)
{
  Left.writeMicroseconds(1700);
  Right.writeMicroseconds(1700);
  delay(time);
}

void moveBackward(int time)
{
  Left.writeMicroseconds(1300);
  Right.writeMicroseconds(1700);
  delay(time);
}

void loop(){

  digitalWrite(trigger, HIGH);
  delay(10);
  digitalWrite(trigger, LOW);

  duration = pulseIn(echo, HIGH);
  distance = (duration/2) / 29.1;

  Serial.println(distance);

  if(distance < 15) {
    moveBackward(2000);
  }
}