2.1 ros+px4 simulation - Fixed Point flight control

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introduction ： This section is performed after the simulation environment has been installed . The installation of simulation environment can refer to the video explanation ： Links are as follows

**

Detailed explanation of environment installation and fixed-point flight code

The video starts with the little turtle routine , The topic subscription and publication are described in detail , The code in this section is analyzed later
video ： Code details

1、 Enter into Firmware Under the folder , start-up gazebo Simulation environment ：

 make px4_sitl_default gazebo

2、 start-up MAVROS Simulation

 `roslaunch mavros px4.launch fcu_url:="udp://:[email protected]:14557"`

3、 Start flight node

rosrun offboard_node offboard_node

4、 code annotation ：

// The relevant header file contains 
#include <ros/ros.h>
#include <geometry_msgs/PoseStamped.h>
#include <mavros_msgs/CommandBool.h>
#include <mavros_msgs/SetMode.h>
#include <mavros_msgs/State.h>
 
mavros_msgs::State current_state;

// Callback function 
void state_cb(const mavros_msgs::State::ConstPtr& msg){
    
    current_state = *msg;
}
 
int main(int argc, char **argv)
{
    
		// Initialize node 
    ros::init(argc, argv, "offb_node");
    // Create node handle 
    ros::NodeHandle nh;
 		// Create subscribers , Subscribe to the topic mavros/state
    ros::Subscriber state_sub = nh.subscribe<mavros_msgs::State>
            ("mavros/state", 10, state_cb);
    // Create a publisher , Release "mavros/setpoint_position/local" topic of conversation 
    ros::Publisher local_pos_pub = nh.advertise<geometry_msgs::PoseStamped>
            ("mavros/setpoint_position/local", 10);
    // Create a client , This client is used to request PX4 Unlock the UAV  
    ros::ServiceClient arming_client = nh.serviceClient<mavros_msgs::CommandBool>
            ("mavros/cmd/arming");
    // Create a client , This client is used to request entry offboard Pattern 
    ros::ServiceClient set_mode_client = nh.serviceClient<mavros_msgs::SetMode>
            ("mavros/set_mode");
 
    // collocation rate.sleep() function , Realization 20Hz Cycle of frequency ;
    ros::Rate rate(20.0);
 
    //  Wait for flight control connection 
    while(ros::ok() && !current_state.connected){
    
        ros::spinOnce();
        rate.sleep();
    }
 
 	  // Create a variable , This variable is the position where the UAV is about to take off , The starting point is the power on time of the UAV 
    geometry_msgs::PoseStamped pose;
    pose.pose.position.x = 0;
    pose.pose.position.y = 0;
    pose.pose.position.z = 2;
    
    // Pre release desired location information , Give the drone a target point 
    //send a few setpoints before starting
    for(int i = 100; ros::ok() && i > 0; --i){
    
        local_pos_pub.publish(pose);
        ros::spinOnce();
        rate.sleep();
    }
   
    // Set the client to request the UAV to enter “OFFBOARD” Pattern 
    mavros_msgs::SetMode offb_set_mode;
    offb_set_mode.request.custom_mode = "OFFBOARD";
   
    // Set the customer to ask the UAV to unlock 
    mavros_msgs::CommandBool arm_cmd;
    arm_cmd.request.value = true;
 
 	  // Get the timestamp 
    ros::Time last_request = ros::Time::now();
 
    while(ros::ok()){
    
        //if Statement loop request to enter OFFBOARD Pattern , After entering, you will enter else Statement request to unlock the UAV .
        if( current_state.mode != "OFFBOARD" &&
            (ros::Time::now() - last_request > ros::Duration(5.0))){
    
            if( set_mode_client.call(offb_set_mode) &&
                offb_set_mode.response.mode_sent){
    
                ROS_INFO("Offboard enabled");
            }
            last_request = ros::Time::now();
        } else {
    
            if( !current_state.armed &&
                (ros::Time::now() - last_request > ros::Duration(5.0))){
    
                if( arming_client.call(arm_cmd) &&
                    arm_cmd.response.success){
    
                    ROS_INFO("Vehicle armed");
                }
                last_request = ros::Time::now();
            }
        }
       
        // Circularly publish the desired location information ,20Hz frequency 
        local_pos_pub.publish(pose);
 
        ros::spinOnce();
        rate.sleep();
    }
    return 0;
}