Offboard mode in PX4

Nicolas de Palezieux

The px4.launch file does not start up the PX4 stack, it just starts up mavros, which talks to PX4 via mavlink messages.

If you are trying to use PX4 in simulation, you can run `make posix_sitl_default gazebo`. You can then use mavros to talk to PX4 through UDP as you tried to do.

If you are using this on a Snadpragon Flight board (since you mentioned snap_cam), this should also work, after you started PX4 with `mainapp mainapp.config`.

If you are running mavros on a compantion computer (Raspberry Pi / Odroid), you need to change the fcu_url to the appropriate serial address.

Once you have mavros running and connected to your PX4 instance of choice, you can send commands on the ROS topics that mavros offers (see the mavros documentation). This is what the example in

http://dev.px4.io/ros-mavros-offboard.html

does. The given example code is a ROS node, which you compile with `catkin_make` (or `catkin build` if you've installed catkin tools). Check out the ROS documentation to learn how to build your own nodes. You then run your node with

`rosrun <package_name> offb_node.

Hope that helps