README

create3_republisher

What is this?

This package contains a ROS 2 applications capable of republishing ROS 2 entities. It’s designed to work with the iRobot Create 3 robot.

This means that if the robot is publishing on topic /my_robot/odom this application can subscribe to this topic and republish its messages into a new namespace, e.g. /my_republisher/odom. This works also with publishers, services and actions.

For example, with /my_robot/cmd_vel remapped to /my_republisher/cmd_vel, users can then send motion commands to /my_republisher/cmd_vel to move the robot around, or send a ROS 2 action goal to /my_republisher/drive_distance, etc..

Why using this?

ROS 2 middlewares have a tendency to discover all the ROS 2 entities in the network and allocate resources for all of them, even if they don’t need to communicate. This can cause performance issues due to excessive memory allocations, discovery traffic and double delivery of messages. This republisher can be used to get around this problem.

For example, this occurs when having your Create 3 robot connected to a RaspberryPi (or other SBC), which runs applications made of a high number of ROS 2 entities or that deal with very big messages (e.g. the navigation stack, or rtabmap, etc).

IMPORTANT: use this tool only if you experience problems in your setup.

NOTE: Using this tool requires at least some understanding of how to configure ROS 2 application via DDS XML configuration files.

Prerequisites

Your robot and other ROS 2 applications should be on ROS 2 Humble.
You should use Fast-DDS as your RMW on the robot and throughout all your applications. This approach is not RMW-specific, but the instructions and the provided DDS config file are. Use the webserver to check or modify the Create 3 robot RMW (see webserver docs for details)
Ensure that you can discover and communicate via ROS 2 between all your devices before starting. For example:
- If using a RaspberryPi (or other SBC) try pinging the Create 3 robot via usb0 interface with ping 192.168.186.2
- Verify that ros2 topic list shows the Create 3 robot topics

This procedure will use advanced communication configuration, and if stuff wasn’t working before, it will be hard to debug it later. These instructions assume that you didn’t need any custom DDS configuration to get communication working. If that’s not the case, your custom configuration will likely need to be integrated with the provided DDS configuration files, which is not covered by this tutorial.

Connecting the Create 3 Robot and an SBC via the republisher

The following instructions will show how to isolate the robot to discover and communicate only with an entity, the republisher, and ignore all other processes running on your RaspberryPi (or other SBC). Other entities, e.g. your navigation application can then interact with the republisher (i.e. they can subscribe to Create 3 topics, and send requests) without “being discovered by it”. This is the “default setup” for this republisher. The next sections will show examples on how to customize it for other common scenarios.

Build this repository on the RaspberryPi (or other SBC). For example:

mkdir -p ~/ws/src
cd ~/ws/src
git clone https://github.com/iRobotEducation/create3_examples.git
cd ~/ws
colcon build --symlink-install

Modify the Fast-DDS XML profile on the Create 3, through the webserver, to exactly match the fastdds-robot-passive-unicast.xml profile. See webserver docs for details.
Launch the republisher app in a terminal on your RaspberryPi (or other SBC) using the provided fastdds-active-unicast.xml profile. For example:
```
source ~/ws/install/setup.sh
export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export FASTRTPS_DEFAULT_PROFILES_FILE=~/ws/src/create3_examples/create3_republisher/dds-config/fastdds-active-unicast.xml
ros2 daemon stop
ros2 launch create3_republisher create3_republisher_launch.py
```
This command assumes that the Create 3 robot is using the default namespace and it will republish all Create 3 robot names into the /repub namespace.

If your Create 3 robot is running with a namespace, for example /my_robot, and/or you want to change the republication namespace, for example /my_repub, you can do it via command line arguments.
```
ros2 launch create3_republisher create3_republisher_launch.py republisher_ns:=/my_repub robot_ns:=/my_robot
```
IMPORTANT: THE TWO NAMESPACES MUST BE DIFFERENT!!

NOTE: the list of entities that’s republished is defined by the params.yaml file which you’ll find at ~/ws/install/create3_republisher/share/create3_republisher/bringup/params.yaml. Comment or uncomment entries in this file to customize it to your needs.

Run your other applicatios that want to communicate with Create 3 in another terminal of the RaspberryPi (or other SBC) using a passive unicast DDS configuration profile. For example:

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export FASTRTPS_DEFAULT_PROFILES_FILE=~/ws/src/create3_examples/create3_republisher/dds-config/fastdds-passive-unicast.xml
ros2 daemon stop
ros2 topic echo /repub/tf
ros2 action send_goal /repub/drive_distance irobot_create_msgs/action/DriveDistance "{distance: 0.5,max_translation_speed: 0.15}"

OPTIONAL: Connect your laptop and your RaspberryPi (or other SBC) With the setup described so far, you should have your RaspberryPi and your Create 3 robot able to communicate via ROS 2. However, your laptop (or other devices in the network) won’t be able to discover neither the robot nor the SBC. To enable this communication, which again will occurr through the republisher, you will need a DDS configuration file also on your laptop (or other device).
- Get the Wi-Fi IP address of the RaspberryPi (that’s the one you use to SSH into it).
- Create a copy of the fastdds-active-unicast.xml profile, which will be referenced as fastdds-laptop-unicast.xml in the following steps.
- Modify the new fastdds-laptop-unicast.xml file, replacing the IP address in the line <address>192.168.186.2</address> with the RaspberryPi IP address mentioned before. For example <address>192.168.1.212</address>.

Connecting the Create 3 Robot and your laptop via the republisher

If you don’t have a RaspberryPi or other SBC, you can still use the republisher application on your laptop. Most of the instructions presented above remain unchaged, but you will not be able to use the provided fastdds-active-unicast.xml profile for the republisher process. This DDS profile contains hardcoded the usb0 IP address of the Create 3 robot. You will need to modify it to use the Wi-Fi IP address of the Create 3 instead.

Get the Wi-Fi IP address of the Create 3 robot (this is the IP address you use to access the Create 3 webserver).
Create a copy of the fastdds-active-unicast.xml profile, which will be referenced as fastdds-laptop-unicast.xml in the following steps.
Modify the new fastdds-laptop-unicast.xml file, replacing the IP address in the line <address>192.168.186.2</address> with the Create 3 IP address mentioned before. For example <address>192.168.1.103</address>.

Note: these changes to the fastdds-active-unicast.xml profile are very similar to what done in the previous instructions to allow the laptop to communicate with the RaspberryPi. The only, but fundamental, difference is that here we are using the Create 3 IP address, rather than the RaspberryPi IP address.

Notes and Tips

Only the republisher should connect with the robot

IMPORTANT: this republisher is powered by the concept of “unicast discovery” protocols. There must be only 1 DDS profile in your setup that references the Create 3 IP address and it must be used only by the republisher process. Keep this in mind if you need to do further modifications to the configs, besides what described in this page.

Ensure that your discovery info is up-to-date

Run ros2 daemon stop whenever you modify DDS configuration file and/or environment variables.

Why do I see the Create 3 names, but I can’t communicate with them

NOTE: having different applications run with different DDS configuration profiles (as it’s done with the republisher) could mess up the ROS 2 daemon. Don’t blindly trust the output of ros2 topic list and similar commands. Run with --no-daemon when possible and call ros2 daemon stop in every new terminal after setting the DDS configuration profiles.

The “old” Create 3 entity names will not be usable anymore in this configuration. After running those steps, for example, you won’t be able to subscribe to the robot tf topic via ros2 topic echo /tf but only via ros2 topic echo /repub/tf.

Inspecting the ROS graph (e.g. via ros2 topic list) may seem to still show the robot’s topics (e.g. you may see /tf being listed there), but you can notice that subscribing to those topics won’t produce any data. Indeed, querying more information about the topics will show you that what you are seeing is a “subscriber” (that lives on the republisher) and not the robot’s publisher.

pi@raspberrypi:~$ ros2 topic info -v /tf
Type: tf2_msgs/msg/TFMessage

Publisher count: 0

Subscription count: 1

Node name: create3_repub
Node namespace: /repub
Topic type: tf2_msgs/msg/TFMessage
Endpoint type: SUBSCRIPTION
GID: 01.0f.e8.52.41.09.d1.75.01.00.00.00.00.00.19.04.00.00.00.00.00.00.00.00
QoS profile:
  Reliability: BEST_EFFORT
  History (Depth): UNKNOWN
  Durability: VOLATILE
  Lifespan: Infinite
  Deadline: Infinite
  Liveliness: AUTOMATIC
  Liveliness lease duration: Infinite

I have a navigation application with hardcoded Create 3 topic names and I don’t want to change them

If you have a ROS 2 application that has hardcoded Create 3 topics and action names (e.g. /cmd_vel or /my_create3/dock), you don’t necessarily need to modify it to use the republisher. Just change the Create 3 namespace to “something else” and set the republisher namespace as the old robot’s namespace. For example, if you robot has a namespace /my_create3 you can: first of all change its namespace to /my_robot and then run the republisher as:

ros2 launch create3_republisher create3_republisher_launch.py republisher_ns:=/my_create3 robot_ns:=/my_robot

This approach can be used also if the robot didn’t have a namespace to start with! Assign it to a new namespace and then use / as republisher_ns.