PX4-FastRTPS-ROS

This proof of concept aims to extend the bridge PX4-FastRTPS to ROS and test how the exchange of information works between nodes of PX4 and ROS. The PoC has been implemented and tested in a PIXracer for the PX4 side and a couple of PC running Ubuntu 16.04 for micro RTPS agent, ROS2-ROS bridge and the ROS node.

The PoC has been performed over a single message sensor combined for the sake of simplicity.

Scheme

The scheme has 5 nodes involved as shown in the image above:

• uORB: This node is the representation of the publisher(s) that send, in this case, sensor combined messages through uORB protocol.
• micrortps_client is the node that get the information from uORB world, translate it and transmit to the next node in a serialization format understandable for the micro RTPS side of wich is part.
• micrortps_agent as a full member of the DDS world inject the received information publishing the message in the sensor_combined_topic.
• static_bridge is the node of ROS2 (part of the ros1_bridge package) that listen directly whitout previous translation the topic (taking advantage of use of the same RTPS protocol internally) and pass it from ROS 2 to ROS 1.
• sc_ros1_listener a very simple ROS node that listen to the well formed ROS topic, print the info on the screen and publish back into a new topic sensor_combined_topic_back.

NOTE: The same path is followed in reverse from ROS to PX4 for latency estimation.

Requierements

• PX4-Fast RTPS brigde: its necessary work with the eProsima PX4/Firmware fork, please see the README
• ROS2: Install ROS2 with the latest update of its packages from the master branch of this repository.
• ROS from sources: Install ROS from sources (we use kinetic distro).

PX4 side: micro RTPS client

The code of the application that will run in to PX4 side will be found in microRTPS_client folder. To use this code replaces the original one from the client, please see the PX4 Firmware section in the README in case of doubt.

Fast RTPS side: micro RTPS agent

The code of the application that will run as micro RTPS agent will be found in microRTPS_agent folder. To use this code replaces the original one from the agent, please see the Fast RTPS (Raspberry PI application) section in the README in case of doubt.

ROS side

We need to add two packages to our ROS workspace. For that copy them:

$ cd /path/to/px4_to_ros
$ cp -r px4_msgs_ros1 /path/to/ros1/workspace/src/px4_msgs
$ cp -r sensor_combined_ros1 /path/to/ros1/workspace/src/

Compile the packages using:

$ catkin_make_isolated --pkg px4_msgs --install -DCMAKE_BUILD_TYPE=Release
$ catkin_make_isolated --pkg sensor_combined_ros1 --install -DCMAKE_BUILD_TYPE=Release

For launch the application we need to launch in first place roscore in a separate shell:

$ source /path/to/ros1/workspace/install_folder/setup.bash
$ roscore

Now, you can run the listener application with:

$ source /path/to/ros1/workspace/install_folder/setup.bash
$ rosrun sensor_combined_ros1 sc_ros1_listener

ROS2 side

In order to run the ROS2 to ROS1 bridge, you have to add one package and modify other (ros1_bridge package) in your ROS2 worskpace. The package px4_msgs generates all the PX4 messages that are actually supported. To use, copy in this way:

$ cd /path/to/px4_to_ros
$ cp -r px4_msgs_ros2 /path/to/ros2/workspace/src/ros2/px4_msgs
$ cp -r ros1_bridge /path/to/ros2/workspace/src/ros2/

Compile the package px4_msgs with ament using:

$ ament build --symlink-install --only px4_msgs

compile the bridge, please see Building the bridge from source

Now, you can run the bridge application with:

$ source /path/to/ros1/workspace/install_folder/setup.bash
$ source /path/to/ros2/workspace/install_folder/setup.bash
$ static_bridge

Roscore: working in several machines

In due we only need one instance of roscore runnig we need to make some adjustenments to work in separate machines:

Machine that runs roscore need to define:

$ export ROS_MASTER_URI=http://localhost:11311
$ export ROS_HOSTNAME=<LOCAL_IP>

Machine that NOT run roscore need to define:

$ export ROS_MASTER_URI=http://<ROSCORE_MACHINE_IP>:11311
$ export ROS_HOSTNAME=<LOCAL_IP>