Node-RED ROS 2 Plugin

This project is started as an fork of node-red-ros2-plugin from eProsima. We removed the Integration Service and added ROS service client and ROS action client using the Java Script ROS API, rclnodejs.

Installation

Checking if Node-Red is already Installed

It may happen that the compose-up command fails because port 1880 is already in use. The application that caused this error can be determined with the following command:

sudo netstat -tulpn

This command will print out a table with all used ports at moment. The 3. column shows on which ip and port an application is listening:

tcp   0   0 0.0.0.0:1880    0.0.0.0:*    LISTEN   27803/node-red 

In this case, the port is already in use by another Node Red installation. If this instance is installed on a Debian-based system, it can be uninstalled by :

sudo apt remove node-red 

Checking on a EduArt's Robot

If Node-Red should be installed on a EduArt's Robot than you have to connect to the robot first using command ssh. For this the robot's IP address is required. For installing or updating the Node-Red software a internet connection is required, this means usually the robot is connected by an ethernet connection to your local network. What leads in a IP address assigned by the DHCP server of your network. Either get the IP address from the router (usually by using its web interface) or use the tool nmap:

sudo nmap -sn <your local subnet, for example: 192.168.1.0/24>

A list of all devices connected to your local subnet is shown. Pick the robot's IP. We assume the robot's IP is 192.168.0.100 from this point on. Connect to the robot using:

ssh [email protected]

Now use the instruction from section before.

Installing EduArt's Node-Red ROS2 Plugin

The plugin comes with a Node-Red installation deployed in a Docker image. This makes it easy to install and use. First get the open source code by cloning the repository on your target machine, most likely on a robot:

git clone https://github.com/EduArt-Robotik/edu_nodered_ros2_plugin.git 

Go inside the docker folder where the compose file is located:

cd edu_nodered_ros2_plugin/docker/ 

Then execute the command:

docker compose up

The Node-Red web server will start up. The docker container will be autostart after a reboot or if an error occurred.

Updating EduArt's Node-Red ROS2 Plugin

Checking

To be always up to date, it is worth checking the system regularly for updates. To do this, change to the "home" directory and then into the folder "edu_nodered_ros2_plugin" and execute the commands:

git checkout master
git pull origin

The output will tell you if there is a new version of the code.

Update

Don't worry previously performed work in Node-Red will be preserved as the data is stored outside the Docker container. First remove current version. Go into the folder where the docker compose file is located:

cd edu_nodered_ros2_plugin/docker/ 

Now the new version can be started by the command:

docker compose up

The container will be stopped and the new pulled and started.

Usage

Note : we assume that the Node-Red server is running on the IP address 192.168.0.100. If this differs to your network configuration please replace the IP address accordingly.

Open a browser you like enter the following address to visit the Node-Red web interface: http://192.168.0.100:1880. This will open the typical NodeRed window.

Remember : your computer needs to be in the same Network as the robot. This could now also be the internal Router as the robot needs no internet anymore.

Node-RED palette

The main concepts associated with Node-RED operation are explained here. The plugin nodes are displayed on the Node-RED palette as shown in the image. From there, they can be dragged into the flow workspace.

These palette represents the basic ROS client features like publishing and subscribing to a ROS topic, requesting an ROS service or performing a ROS action. With this features it should be possible to control existing ROS system like a robot and to use higher level application like the Nav2 (Navigation Stack).

Note : the text that labels the node, changes from palette to workspace, and may change depending on the node configuration.

Publishing and Subscribing to an ROS Topic

In order the publish or subscribe data we need first to specify the associated type. The topic type is represented by the node ROS2 Type. It is required that the ROS2 Type is connected to the Publisher or Subscriber Node.

Choosing a ROS2 type

	This node represents a specific ROS2 Types installed on the system. Once in the workspace, its set up dialog can be opened by double clicking over it.
	The dialog provides a Package drop-down control where all ROS2 msg packages are listed. Once a package is selected the Message drop-down control allows selection of a package specific message. In this example the package selected is edu_robot. From this package the RobotStatusReport message is selected.
	Once the dialog set up is saved, the node label changes to highlight the selected type in a package/message pattern.

Injecting a type instance into the pipeline

Node-RED pipelines start in source nodes. The most popular one is the inject node which requires the user to manually defined each field associated to the type. In order to simplify this a specific node is introduced:

This node mimics the inject node behaviour but automatically populates the input dialog with the fields associated with any type node linked to it. For example, if we wire together a ROS2 Inject and a ROS2 Type as shown in the figure:

The associated dialogs are populated with the linked type fields and types. For example the twist message is populated as:

ROS2 nodes: General Settings

In order to interact with a ROS2 environment we must specify the same domain id in use for that environment.

The domain id is a number in the range [0, 166] that provides isolation for ROS2 nodes. It defaults to 0 and its main advantage is reduce the incomming traffic for each ROS2 node, discharging them and speeding things up.

Another key concepts in the ROS2 environment are:

• topic one. A topic is a text string ROS2 nodes use to notify all other nodes in which data they are interested. When a ROS2 node wants to send or receive data it must specify:

• Which type is the data they want receive. For example the edu_robot/RobotStatusReport we introduced above.
• Topic associated with the data. For example /status_report, but in ROS2 topics are often decorated using namespaces to simplify identification, as in /eduard/red/status_report.

• Quality of Service (QoS). Those are policies that allow fine tunning of the communication between nodes. For example:
  • History QoS allows to discard messages if only the most recent one is meaningful for our purposes.
  • Reliable QoS enforces message reception by resending it until the receiver acknowledges it.
  • Durability QoS assures messages published before the receiver node creation would be delivered.

Note: ROS2 nodes can only communicate if their respective QoS are compatible. Information on QoS compatibility is available here.

ROS2 Subscriber

	This node represents a ROS2 subscriber. It is able to subscribe on a specific topic and receive all messages published for it.
	The dialog provides controls to configure: Topic Note that the backslash / typical of ROS2 topics is not necessary Domain ID Selected globally via the configuration node explained above QoS The +add button at the bottom adds new combo-boxes to the control where the available options for each policy can be selected

Example

This example shows how to subscribe to an topic and display it using the debug node. It is based on the available topics of an EduArt's robot like Eduard.

ROS2 Publisher

	This node represents a ROS2 publisher. It is able to publish messages on a specific topic with specific QoS
	The dialog provides controls to configure: Topic Note that the backslash / typical of ROS2 topics is not necessary Domain ID Selected globally via the configuration node explained above QoS The +add button at the bottom adds new combo-boxes to the control where the available options for each policy can be selected

Example

This example shows how to publish to an topic and display the published message using the debug node. It is based on the available topics of an EduArt's robot like Eduard.

ROS2 Service Client

In order to call or request an ROS service we need first to specify the associated type. The service type is represented by the node ROS2 Service Type. It is required that the ROS2 Service Type is connected to the Service Client node.

	This node represents a ROS2 service client. It is able to call a specific service with specific QoS. The connected injection injects the service request only. After a successful service call the service response is output.
	The dialog provides controls to configure: Service Note that the backslash / typical of ROS2 services is not necessary Domain ID Selected globally via the configuration node explained above QoS The +add button at the bottom adds new combo-boxes to the control where the available options for each policy can be selected

Example

This example shows how to call a service and displays the response using a debug node. It is based on the available topics of an EduArt's robot like Eduard. In this example the robot is switched in mode autonomous drive.

ROS2 Action Client

In order to perform a ROS action we need first to specify the associated type. The action type is represented by the node ROS2 Action Type. It is required that the ROS2 Action Type is connected to the Action Client node.

	This node represents a ROS2 action client. It is able to perform a specific action with specific QoS. The connected injection injects the action goal request only. After a accepted action goal the action feedback and the final result is outputted.
	The dialog provides controls to configure: Action Note that the backslash / typical of ROS2 topics is not necessary Domain ID Selected globally via the configuration node explained above QoS The +add button at the bottom adds new combo-boxes to the control where the available options for each policy can be selected

Example

This example shows how to perform a action and displays the feedback and result using two debug nodes. It is based on the ROS action tutorial turtle sim. If you want to reproduce it the turtle sim node has to be launched like in the tutorial.

ROS2 Examples

Don't hit the Wall