int MODE = 8;

int left_motor_in = 6;
int left_motor_out = 9;

int right_motor_in = 3;
int right_motor_out = 5;

void setup() {
  Serial.begin(9600);
  Serial.println("Start");
  init_motor();
}

void loop() {
  left_motor_go(250);
  right_motor_go(250);
}
  
void init_motor(){
  pinMode(left_motor_in, OUTPUT);
  pinMode(left_motor_out, OUTPUT);
  
  pinMode(right_motor_in, OUTPUT);
  pinMode(right_motor_out, OUTPUT);

  pinMode(MODE, OUTPUT);
  digitalWrite(MODE, HIGH);
  }

//range:0<value<255
void left_motor_go(int motor_speed){
  analogWrite(left_motor_in, motor_speed);
  digitalWrite(left_motor_out, LOW);
 }
//range:0<value<255
void right_motor_go(int motor_speed){
  analogWrite(right_motor_in, motor_speed);
  digitalWrite(right_motor_out, LOW);
}