https://github.com/DroidAITech/ROS-Academy-for-Beginners

我的是 错误如下
kenneth@kenneth-lenovo-g50-75m:~/catkin_ws$ rosdep install --from-paths src --ignore-src --rosdistro=melodic -y 
ERROR: the following packages/stacks could not have their rosdep keys resolved to system dependencies: robot_sim_demo: 
Cannot locate rosdep definition for [yocs_cmd_vel_mux] navigation_sim_demo: Cannot locate rosdep definition for [gmapping] 
slam_sim_demo: Cannot locate rosdep definition for [hector_mapping]

解决办法：

关于在Ubuntu 18.04 Melodic上编译的问题搞了好久，方法如下：
1、需要在github上clone3个package到~/catkin_ws/src，地址如下：
https://github.com/ros-perception/slam_gmapping.git
https://github.com/ros-perception/openslam_gmapping.git
https://github.com/tu-darmstadt-ros-pkg/hector_slam.git
2、修改ROS-Academy-for-Beginners/slam_sim_demo下的package.xml，增加如下项：
<build_depend>controller_manager</build_depend>
<build_depend>gazebo_ros</build_depend>
<build_depend>slam_karto</build_depend>
<build_depend>gmapping</build_depend>
<build_depend>amcl</build_depend>
<build_depend>hector_mapping</build_depend>

然后重新执行

rosdep install --from-paths src --ignore-src --rosdistro=melodic -y

就会正常安装没有错误了

运行roslaunch robot_sim_demo robot_spawn.launch

提示Error in REST request出错

• 将服务器~/.ignition/fuel/config.yaml从https://api.ignitionfuel.org更新到https://api.ignitionrobotics.org

• $ sudo gedit ~/.ignition/fuel/config.yaml
  

    # url： https://api.ignitionfuel.org  # 注释掉此行
      url: https://api.ignitionrobotics.org  # 新增此行