笔者使用的是自定义的机器人分布式开发框架，要对及ROS ，所以用到了 mqtt 转ROS 。
安装包

安装paho-mqtt

pip install paho-mqtt

安装ROS1 Python库

sudo apt-get install python-rospy

编写python程序监听 mqtt的消息 ，并转换成 ROS的消息格式发布出去。
mqtt_cmdvel.py

#!/usr/bin/env python
import paho.mqtt.client as mqtt
import rospy
import json
from geometry_msgs.msg import Twist
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))

def on_message(client, userdata, msg):
    # 将mqtt格式转换为ROS1格式
    if (msg.topic == "/cms/vel"):
        data = json.loads(msg.payload.decode("utf-8"))
        linear = data['vel']
        angular = data['ang']
        twist = Twist()
        twist.linear.x = float(linear)
        twist.angular.z = float(angular)
        # 发布到ROS1主题
        pub.publish(twist)
if __name__ == '__main__':
    # 初始化ROS1节点
    rospy.init_node('mqtt_twist')
    # 创建ROS1发布者
    pub = rospy.Publisher('turtle1/cmd_vel', Twist, queue_size=10)
    # 创建mqtt客户端
    client = mqtt.Client()
    # 设置回调函数
    client.on_connect = on_connect
    client.on_message = on_message
    # 连接mqtt代理
    client.connect("127.0.0.1", port=1883)
     # 订阅mqtt主题  来自客户端 网页 第三方
    client.subscribe("/cmd/vel")
    # 循环等待mqtt消息
    client.loop_forever()

接着执行指令
cd catkin_ws/src
catkin_create_pkg mqtt_cmddev rospy std_msgs geometry_msgs
将上述mqtt_cmdvel.py 放到创建的scripts 文件夹下
lid@lid-VirtualBox:~/catkin_ws/src$ tree -L 3
.
├── CMakeLists.txt -> /opt/ros/melodic/share/catkin/cmake/toplevel.cmake
└── mqtt_cmddev
├── CMakeLists.txt
├── package.xml
├── scripts
│   └── mqtt_cmdvel.py
└── src

修改CMakeLists.txt

## in contrast to setup.py, you can choose the destination
 catkin_install_python(PROGRAMS
   scripts/mqtt_cmdvel.py
   DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
 )

返回到 catkin_ws 下 执行指令
catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python3
成功编译后，source ~/catkin_ws/devel/setup.bash

rospack list 刷新包名 使包名可见，有些情况下，source bash后依然找不到，需要使用此条指令刷新。