   }
   /* Node handle setting. */
   nh.initNode(); // First setup the node handle.
-  nh.subscribe(sub); // Start subscribe the motor_driver topic.
+  nh.subscribe(sub); // Start subscribe the "steer_ctrl" topic.
 }
 
 void loop() {
-  //nh.spinOnce(); // Check topic and if change it, run the call back function.
-  steer(RIGHT);
-  delay(1000);
-  steer(LEFT);
-  delay(1000);
+  nh.spinOnce(); // Check topic and if change it, run the call back function.
 }
 
 /**

const int ccw_minus = 6;

/* Declare proto type functions. */
void steer(const char direction); // Write pulse to the stepping motor.
void motorCb(const geometry_msgs::Twist& msg); // Call back function of the motor_driver topic.

/* Declare global constants. */
const unsigned int PULSE_FREQUENCY = 1000l * 1000 / (PULSE_WIDTH_MICRO_SECOND * 2); // Get frequency of pulse.
/* Declare global variables. */
ros::NodeHandle nh; // The nodeHandle.
ros::Subscriber<geometry_msgs::Twist> sub("motor_driver", &motorCb); // Set subscribe the motor_driver topic.

void setup() {
  /* Set pins Mode. */

 * @author "Yusuke Doi"
 * @param direction Steer to direction.
 */
void gen_pluse(const char direction) {
  switch (direction) {
  case LEFT: // Task steer left.
      noTone(cw_plus); // Unset tone. If don't running tone, not happen.
