error[gazebo-2]

[LevanFather]

when I try to simulation in Gazebo, roslaunch robotis_op_gazebo robotis_op_gazebo_position_control_soccer_field.launch
and error,
hope you can help me,thanks!

[gazebo-2] process has died [pid 22132, exit code 134, cmd /opt/ros/indigo/lib/gazebo_ros/gzserver -u -e ode /opt/ros/indigo/share/gazebo_ros/launch/empty_world.launch __name:=gazebo __log:=/home/levan/.ros/log/8af4c2ac-445c-11e7-b0ff-b82a72f3a021/gazebo-2.log].
log file: /home/levan/.ros/log/8af4c2ac-445c-11e7-b0ff-b82a72f3a021/gazebo-2*.log

Error [ConnectionManager.cc:116] Failed to connect to master in 30 seconds.
Error [gazebo.cc:59] Unable to initialize transport.
Error [gazebo.cc:203] Unable to setup Gazebo
[gazebo_gui-3] process has died [pid 22136, exit code 255, cmd /opt/ros/indigo/lib/gazebo_ros/gzclient __name:=gazebo_gui __log:=/home/levan/.ros/log/8af4c2ac-445c-11e7-b0ff-b82a72f3a021/gazebo_gui-3.log].
log file: /home/levan/.ros/log/8af4c2ac-445c-11e7-b0ff-b82a72f3a021/gazebo_gui-3*.log

[kdaun]

The error states that the program cannot connect to the ROS master. However, by using roslaunch a local ros core is launched (if not already available) and should provide a ROS master. Do you have your ROS_MASTER_URI set to an external adress? You can check that by calling:
echo $ROS_MASTER_URI
in your ROS environment.
Furthermore, which ROS Version and which OS are you using?