Arduino Sainsmart 4WD Robot | MKme.org　　SainSmart Car Kit Instructions
http://www.sainsmart.com/zen/documents/20-011-C56/car-MEGA2560%20english.pdf

CODE：　the MEGA2560 so that you can see the car automatically move forward and avoid the obstacle.

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const int EchoPin = 2; // Ultrasonic signal input
const int TrigPin = 3; // Ultrasonic signal output
const int leftmotorpin1 = 8; //signal output of DC geared motor
const int leftmotorpin2 = 9;
const int rightmotorpin1 = 6;
const int rightmotorpin2 = 7;
int currDist = 0; // distance
void setup() {
 pinMode(EchoPin, INPUT);
 for (int pinindex = 3; pinindex < 8; pinindex++) {
 pinMode(pinindex, OUTPUT); // set pins 3 to 10 as outputs
 }
}
void loop() {
 currDist = MeasuringDistance(); //measure front distance
 if(currDist >20) {
 nodanger(); }
 else if(currDist <10){
 backup();
 randTrun();
 }
 else {
 //whichway();
 randTrun();
 }
}
//measure distance, unit:cm
long MeasuringDistance() {
 long duration;
 //pinMode(TrigPin, OUTPUT);
 digitalWrite(TrigPin, LOW);
 delayMicroseconds(2);
 digitalWrite(TrigPin, HIGH);
 delayMicroseconds(10);
 digitalWrite(TrigPin, LOW);
 //pinMode(EchoPin, INPUT);
 duration = pulseIn(EchoPin, HIGH);
 return duration / 29 / 2;
}
// forward
void nodanger() {
 digitalWrite(leftmotorpin1, HIGH);
 digitalWrite(leftmotorpin2, LOW);
 digitalWrite(rightmotorpin1, HIGH);
 digitalWrite(rightmotorpin2, LOW);
 delay(1000);
 return;
} 
//backward
void backup() {
 digitalWrite(leftmotorpin1, LOW);
 digitalWrite(leftmotorpin2, HIGH);
 digitalWrite(rightmotorpin1, LOW);
 digitalWrite(rightmotorpin2, HIGH);
delay(500);}
void totalhalt() {
 digitalWrite(leftmotorpin1, HIGH);
 digitalWrite(leftmotorpin2, HIGH);
 digitalWrite(rightmotorpin1, HIGH);
 digitalWrite(rightmotorpin2, HIGH);
 return;
 delay(500);
} 
//turn left 
void body_lturn() {
 digitalWrite(leftmotorpin1, LOW);
 digitalWrite(leftmotorpin2, HIGH);
 digitalWrite(rightmotorpin1, HIGH);
 digitalWrite(rightmotorpin2, LOW);
 delay(500);
 totalhalt();
} 
//turn right
void body_rturn() {
 digitalWrite(leftmotorpin1, HIGH);
 digitalWrite(leftmotorpin2, LOW);
 digitalWrite(rightmotorpin1, LOW);
 digitalWrite(rightmotorpin2, HIGH);
 delay(500);
 totalhalt();
} 
void randTrun(){
 long randNumber;
 randomSeed(analogRead(0));
 randNumber = random(0, 10);
 if(randNumber > 5) {
 body_rturn();
 }
 else
 {
 body_lturn();
 }
}