#include <ros/ros.h>
#include <geometry_msgs/Twist.h>

int main(int argc, char *argv[]){
    ros::init(argc, argv, "quadrotor_obstacle_avoidance");
    
    ros::NodeHandle node;
    ros::Publisher cmd_pub = node.advertise<geometry_msgs::Twist>("cmd_vel", 10);
    
    ros::Duration(1).sleep();
    
    geometry_msgs::Twist cmd;
    
    cmd.linear.z = 5;
    cmd_pub.publish(cmd);
    ros::Duration(5).sleep();
    
    cmd.linear.z = 0.0;
    cmd_pub.publish(cmd);
    ros::Duration(5).sleep();

    return 0;
}


#include <ros/ros.h>
#include <geometry_msgs/Twist.h>

namespace quadrotor_obstacle_avoidance {

int main(int argc, char *argv[]){
    ros::init(argc, argv, "quadrotor_obstacle_avoidance");
    
    ros::NodeHandle node;
    ros::Publisher cmd_pub = node.advertise<geometry_msgs::Twist>("cmd_vel", 10);
    
    geometry_msgs::Twist cmd;
    
    cmd.linear.z = 0.5;
    cmd_pub.publish(cmd);
    ros::Duration(5);
    
    cmd.linear.z = 0.0;
    cmd_pub.publish(cmd);
    ros::Duration(5);

    return 0;
}

};

--- 
+++ 
@@ -1,7 +1,5 @@
 #include <ros/ros.h>
 #include <geometry_msgs/Twist.h>
-
-namespace quadrotor_obstacle_avoidance {
 
 int main(int argc, char *argv[]){
     ros::init(argc, argv, "quadrotor_obstacle_avoidance");
@@ -9,17 +7,18 @@
     ros::NodeHandle node;
     ros::Publisher cmd_pub = node.advertise<geometry_msgs::Twist>("cmd_vel", 10);
     
+    ros::Duration(1).sleep();
+    
     geometry_msgs::Twist cmd;
     
-    cmd.linear.z = 0.5;
+    cmd.linear.z = 5;
     cmd_pub.publish(cmd);
-    ros::Duration(5);
+    ros::Duration(5).sleep();
     
     cmd.linear.z = 0.0;
     cmd_pub.publish(cmd);
-    ros::Duration(5);
+    ros::Duration(5).sleep();
 
     return 0;
 }
 
-};
Fix building error of node
