[ERROR]: Client [/mavros] wants topic /State to have datatype/md5sum [mavros_msgs/State/4048c9de2a16f4ae8e0538085ebf1b97], but our version has [mavros_msgs/State/18326976df9d29249efc939e00342cde]. Dropping connection.

大概就是这样的错误
这个问题的原因在于不同的ROS分布改变了可视化标记的MD5Sum值，以下为解决方案：

1.找到melodic的md5sum，转到/opt/ros/melodic/include/mavros_msgs/State.h,找到对应的md5sum的值，即错误中的18326976df9d29249efc939e00342cde

2.用报错中期望的md5sum取代，即用

18326976df9d29249efc939e00342cde代替4048c9de2a16f4ae8e0538085ebf1b97

3.将功能包重新编译：catkin_make