Create3 Republisher: A Savior and A Curse?

[slowrunner]

Since running the Create3 Republisher, I have rarely ever seen the Create3 CPU at 100% and have not detected the Create3 failing to respond to a /cmd_vel topic. I consider the Create3 Republisher/DiscoveryServer the savior of the TurtleBot4.

Before the Discovery Server/Republisher configuration I could not keep the Create3 from crashing when I attempted heavy topic traffic on the Raspberry Pi or between the Raspberry Pi and the remote visualization platform (such as stereo depth "images" to RTABmap on the Pi, or point-cloud mapped images from RTABmap to Rviz2 on the visualization platform).

BUT, the republisher is introducing a delay between the Create3 sensors and the data consumers. Even though the timestamps are synchronized, the actual republished Create3 sensor data is delayed compared with LIDAR data that does not go through the republisher.

I don't know what is causing the navigation package to be flakey starting up, but my other robots (that do not need a republisher concept) never have the startup issue we are seeing in both Humble and Jazzy TurtleBot4 robots.

I am wondering if the Republisher needs to run at a higher priority (if that is even possible), or navigation needs some special "TurtleBot4 Configuration", but I am having flashbacks to my pre-discovery-server-republisher time with the Create3.

The TurtleBot4 is capable of great things, but we will only succeed to do great things if the platform is reliable.

As a side: At the same time that iRobot was cancelling the Create3, I had a proposal into iRobotEd to make a "non-ROS2-Create3" available that would put all ROS communication on the Raspberry Pi which has the resources needed to work in a busy RMW situation. I still wish for this configuration. The Create3 is a great platform with a weak processor at its heart.

Just sayin'

@hilary-luo @alsora @brianabouchard @SteveMacenski

Background That I Don't Understand, but originally led me to trust the TurtleBot4/Create3 will be a solid, well tested platform for my robotic adventures:
ROSCon-2023-keynote-iRobot-Create-3-Robot-Challenges-and-Solutions.pdf