Arduino Uno and ROS2 bridge

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Given that you use Arduino only to drive motors I would recommend using ros2_control instead of micro-ROS. ros2_control provides a hardware_interface in which you implement write/read methods (send commands/receive encoder readings). You just need to implement a motor control and communication protocol for each joint.

The advantage of the ros2_control is that you bring the control complexity from the Arduino board to the Linux board. Then, you can easily load off-the-shelf controllers or create your own. Furthermore, simulation software such as Webots and Gazebo have ros2_control already implemented so you just need to load controllers (great for controller development and sim2real transfer).

To give you more perspective on off-the-shelf controllers, a typical example of a ros2_control controller would be diff_drive_controller. An amazing thing about diff_drive_controller and other ros2_controllers is that they are really well implemented. E.g. diff_drive_controller creates Twist and Odometry topics, but also publishes TFs, supports velocity, acceleration, and jerk limits, implements velocity command timeout behavior, and much more.

See more about ros2_control:
http://control.ros.org/

Would you consider using a Teensy 4 instead of the Uno? Teensy works with micro-ros, and you’ll likely be able to reuse most of the code you wrote for the Arduino. On the downside, you’ll have a little extra work to learn the Teensy and you might run into a few other issues that will require resolving.

I used a lot of different stuff on 8bits and 32 bits ardiuno through raspberry pi

32 bits = micro-ros 8 bits = Python Firmata mixed with ros2 (just import FIrmata while using ros2)

FYI, there's a ton of ways to do this but I feel FIrmata is easiest option for you since you just need motors+encoder, right? Firmata is simple like that.