RPLIDAR C1 with Raspberry PI 4 and ROS2

The Github repository is Slamtec RPLIDAR ros2.

I followed "How to Install" both in the Client "Intel I9 with Ubuntu 22.04" and in the Host "Raspberry PI 4 - 1 Gigabyte" with Ubuntu 22.04".

On the Client everything went well and after 20 minutes I was able to view the real time laser scan on rviz2

On the contrary I was't so lucky on the Host, where I got stuck at the step:

cd ~/ros2_ws/
source /opt/ros/humble/setup.bash
colcon build --symlink-install

 The "colcon build --simlink-install" lasted for more than 4 hours (against about 30 seconds on the Client) and then crashed, for an evident lack of memory.

After some research and thanks to ChatGPT suggestions, I realized I had the following options:

1. cross compile in my Ubuntu 22.04 amd64 (which I called Client) to target Ubuntu 22.04 arm64v8
2. buy a Raspberry PI 4 - 4 GB
3. build the RPLIDAR package in a docker container based on Ubuntu 22.04 Jammy arm64v8.

I considered 2. as a defeat while 1.isn't supported in ros2 - humble

Read the third option in Details.

Installing ROS2 Humble (see the Details) on both Host (Raspberry PI 4 with Ubuntu 22.04 OS arm64) and Client (Intel I9 with Ubuntu 22.04 OS amd64) was easy, but the problems arose during testing.

Test using "talker" and "listener" as described here  ROS2 Humble - Ubuntu Install Debs went fine on the same machine but failed on different machines (e.g. talker on Client and listener on Host or viceversa). 

After some struggling (1 full day of "change" and "test") I realized that Multicast was enabled on both the machines on all their interfaces but it didn't work. 

The confirmation that Multicast didn't work on my network came from: 

ros2 multicast receive

 on a machine and

ros2 multicast send

 on the other one as "receive". In fact the receiver received ... nothing!

Reading a lot on the Web I realized that many WiFi routers need a setting, whose name not always is Multicast (it would be too easy) but uPnP. 

Fortunately my router had this setting and, after enabling it, all the tests worked fine.

I know that 1 Gigabyte is not that much, especially if the ROS2 Nodes increase in number, but I want to try all the same.

Anyway, preparing a 64 MB SD card using the app Raspberry Imager was pretty easy and in half an hour I got my headless OS (without desktop) perfectly working and WiFi connected.