# 将自定义消息从 MOVROS 发送到 PX4
按照 Source Installation 中的指导,从 mavlink/mavros (opens new window) 安装“ROS Kinetic”版本。
- **Ubuntu:**18.04
- **ROS:**Melodic
- PX4 Firmware: 1.9.0
However these steps are fairly general and so it should work with other distros/versions with little to no modifications. :::
# MAVROS 安装
Follow Source Installation instructions from mavlink/mavros (opens new window) to install "ROS Kinetic".
# MAVROS
首先,我们创建一个新的MAVROS 插件,在keyboard_command.cpp(workspace/src/mavros/mavros_extras/src/plugins)示例中添加以下代码:
代码功能是从ROS消息主题
/mavros/keyboard_command/keyboard_sub
中订阅了一个字符消息,并且将其作为MAVLink 消息发送出去。#include <mavros/mavros_plugin.h> #include <pluginlib/class_list_macros.h> #include <iostream> #include <std_msgs/Char.h> namespace mavros { namespace extra_plugins{ class KeyboardCommandPlugin : public plugin::PluginBase { public: KeyboardCommandPlugin() : PluginBase(), nh("~keyboard_command") { }; void initialize(UAS &uas_) { PluginBase::initialize(uas_); keyboard_sub = nh.subscribe("keyboard_sub", 10, &KeyboardCommandPlugin::keyboard_cb, this); }; Subscriptions get_subscriptions() { return {/* RX disabled */ }; } private: ros::NodeHandle nh; ros::Subscriber keyboard_sub; void keyboard_cb(const std_msgs::Char::ConstPtr &req) { std::cout << "Got Char : " << req->data << std::endl; UAS_FCU(m_uas)->send_message_ignore_drop(req->data); } }; } // namespace extra_plugins } // namespace mavros PLUGINLIB_EXPORT_CLASS(mavros::extra_plugins::KeyboardCommandPlugin, mavros::plugin::PluginBase)
Edit mavros_plugins.xml (in workspace/src/mavros/mavros_extras) and add the following lines:
<class name="keyboard_command" type="mavros::extra_plugins::KeyboardCommandPlugin" base_class_type="mavros::plugin::PluginBase"> <description>Accepts keyboard command.</description> </class>
Edit CMakeLists.txt (in workspace/src/mavros/mavros_extras) and add the following line in
add_library
.add_library( ... src/plugins/keyboard_command.cpp )
Inside common.xml in (workspace/src/mavlink/message_definitions/v1.0), copy the following lines to add your MAVLink message:
... <message id="229" name="KEY_COMMAND"> <description>Keyboard char command.</description> <field type="char" name="command"> </field> </message> ...
# PX4 修改
Inside common.xml (in PX4-Autopilot/mavlink/include/mavlink/v2.0/message_definitions), add your MAVLink message as following (same procedure as for MAVROS section above):
... <message id="229" name="KEY_COMMAND"> <description>Keyboard char command.</description> <field type="char" name="command"> </field> </message> ...
Remove common, standard directories in (PX4-Autopilot/mavlink/include/mavlink/v2.0).
rm -r common rm -r standard
git 克隆"mavlink_generator"到你想要的文件夹下并执行。
git clone https://github.com/mavlink/mavlink mavlink-generator cd mavlink-generator python mavgenerate.py
你会看到一个“MAVLink Generator”应用程序窗口:
- For XML, "Browse" to /PX4-Autopilot/mavlink/include/mavlink/v2.0/message_definitions/standard.xml.
- For Out, "Browse" to /PX4-Autopilot/mavlink/include/mavlink/v2.0/.
- Select Language C
- Select Protocol 2.0
- Check Validate
Then, press Generate. You will see common, and standard directories created in /PX4-Autopilot/mavlink/include/mavlink/v2.0/.
Make your own uORB message file key_command.msg in (PX4-Autopilot/msg). 示例中的“key_command.msg”文件只包含以下代码:
char cmd
Then, in CMakeLists.txt (in PX4-Autopilot/msg), include
set( ... key_command.msg )
Edit mavlink_receiver.h (in PX4-Autopilot/src/modules/mavlink)
... #include <uORB/topics/key_command.h> ... class MavlinkReceiver { ... private: void handle_message_key_command(mavlink_message_t *msg); ... orb_advert_t _key_command_pub{nullptr}; }
Edit mavlink_receiver.cpp (in PX4-Autopilot/src/modules/mavlink). 这是 PX4 接收 ROS 发送过来的 MAVLink 消息的地方,并且将消息作为 uORB 主题发布。
... void MavlinkReceiver::handle_message(mavlink_message_t *msg) { ... case MAVLINK_MSG_ID_KEY_COMMAND: handle_message_key_command(msg); break; ... } ... void MavlinkReceiver::handle_message_key_command(mavlink_message_t *msg) { mavlink_key_command_t man; mavlink_msg_key_command_decode(msg, &man); struct key_command_s key = {}; key.timestamp = hrt_absolute_time(); key.cmd = man.command; if (_key_command_pub == nullptr) { _key_command_pub = orb_advertise(ORB_ID(key_command), &key); } else { orb_publish(ORB_ID(key_command), _key_command_pub, &key); } }
像其他示例一样订阅你自己的uORB主题。 For this example lets create the model in (/PX4-Autopilot/src/modules/key_receiver). In this directory, create two files CMakeLists.txt, key_receiver.cpp. 两个文件如下所示。
-CMakeLists.txt
px4_add_module( MODULE modules__key_receiver MAIN key_receiver STACK_MAIN 2500 STACK_MAX 4000 SRCS key_receiver.cpp DEPENDS platforms__common )
-key_receiver.cpp
#include <px4_config.h> #include <px4_tasks.h> #include <px4_posix.h> #include <unistd.h> #include <stdio.h> #include <poll.h> #include <string.h> #include <math.h> #include <uORB/uORB.h> #include <uORB/topics/key_command.h> extern "C" __EXPORT int key_receiver_main(int argc, char **argv); int key_receiver_main(int argc, char **argv) { int key_sub_fd = orb_subscribe(ORB_ID(key_command)); orb_set_interval(key_sub_fd, 200); // limit the update rate to 200ms px4_pollfd_struct_t fds[1]; fds[0].fd = key_sub_fd, fds[0].events = POLLIN; int error_counter = 0; while(true) { int poll_ret = px4_poll(fds, 1, 1000); if (poll_ret == 0) { PX4_ERR("Got no data within a second"); } else if (poll_ret < 0) { if (error_counter < 10 || error_counter % 50 == 0) { PX4_ERR("ERROR return value from poll(): %d", poll_ret); } error_counter++; } else { if (fds[0].revents & POLLIN) { struct key_command_s input; orb_copy(ORB_ID(key_command), key_sub_fd, &input); PX4_INFO("Recieved Char : %c", input.cmd); } } } return 0; }
For a more detailed explanation see the topic Writing your first application.
Lastly add your module in the default.cmake file correspondent to your board in PX4-Autopilot/boards/. For example for the Pixhawk 4 add the following code in PX4-Autopilot/boards/px4/fmu-v5/default.cmake:
MODULES ... key_receiver ...
测试是否从你的 ROS 话题中接收到 a
字符。
# 构建
# Build for ROS
In your workspace enter:
catkin build
.在此之前,你必须设置你的“px4.launch”(/workspace/src/mavros/mavros/launch)文件。 编辑“px4.launch”文件如下: 如果你使用USB来连接你的电脑和Pixhawk,你必须设置“fcu_url”如下所示。 但是,如果你使用CP2102来连接你的电脑和Pixhawk,你必须将“ttyACM0” 替换为"ttyUSB0"。 修改“gcs_url”是为了连接你的 Pixhawk 和 UDP,因为串口通信不能同时接收 MAVROS 和 nutshell。
Write your IP address at "xxx.xx.xxx.xxx"
... <arg name="fcu_url" default="/dev/ttyACM0:57600" /> <arg name="gcs_url" default="udp://:14550@xxx.xx.xxx.xxx:14557" /> ...
# PX4 编译
Build PX4-Autopilot and upload in the normal way.
For example, to build for Pixhawk 4/FMUv5 execute the following command in the root of the PX4-Autopilot directory:
make px4_fmu-v5_default upload
# Running the Code
Next test if the MAVROS message is sent to PX4.
# Running ROS
- In a terminal enter
roslaunch mavros px4.launch
- 在第二个终端中运行:这意味着以“std_msgs/Char”消息类型发布97(ASCII码的‘a')到ROS主题“/mavros/keyboard_command/keyboard_sub” “-r 10”意味着以“10Hz”频率持续发布。
rostopic pub -r 10 /mavros/keyboard_command/keyboard_sub std_msgs/Char 97
# PX4 运行
通过UDP进入Pixhawk 的 nutshell。 用你的IP地址替换xxx.xx.xxx.xxx
cd PX4-Autopilot/Tools ./mavlink_shell.py xxx.xx.xxx.xxx:14557 --baudrate 57600
After few seconds, press Enter a couple of times. 你会看到终端中以下提示:
nsh> nsh>
输入“key_receiver”命令来运行你的订阅模块。
nsh> key_receiver
Check if it successfully receives a
from your ROS topic.