19.1.4. Starting Simulation

Hint

If launching gazebo from ROS, ROS is not able to kill the gazebo node without escalating to SIGTERM. This happens after a 15s timeout. If you do not have the time to wait for so long, you can modifiy /opt/ros/noetic/lib/python3/dist-packages/roslaunch/nodeprocess.py and change DEFAULT_TIMEOUT_SIGINT to some value you are willing to wait.

General Launch Setup

Vehicle-specific nodes should be launched in namespace “vehicle_name”, for example uuv00 - uuv99.

Each camera node should be launched in namespace “camera_name”, which can be: vertical_camera for HippoCampus, and vertical_camera and front_camera for the BlueROV’s two cameras.

Parameter Setup

Before continuing on the hydrobatic-way-of-live, we need to set some parameters first.

In QGroundControl:

We set Offboard as a flight mode in which remote control (RC) loss is ignored. Thus, fail-safe actions are not triggered.

COM_RCL_EXCEPT=4

Spawning HippoCampus

To start Gazebo with one HippoCampus:

roslaunch hippocampus_sim top_single_vehicle_complete.launch

Path Following example

As an example, we will let the HippoCampus follow an Infinity-shaped path in Gazebo.

Here is the launch file code top_path_following_example.launch explained:

Todo

…

… Let’s start it!

roslaunch hippocampus_sim top_path_following_example.launch

Offboard Mode

The path follower node publishes attitude setpoints. For the uuv_att_control PX4 module to accept externally provided setpoints, the flight mode Offboard mode has to be selected. This mode can only be engaged if the vehicle is already receiving a stream of target setpoints (>2Hz). The vehicle will exit the mode if target setpoints are not received at a rate of >2Hz.

The offboard mode can be selected in QGC.

Arming the Vehicle

Arming is also done in QGC.