How to use source code from Arduino in ROS?

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Thx for the advice, It works fine. I worked through some of the tutorials and I realize that I always have to use these commands:

1. roscore
2. rosrun rosserial_python serial_node.py
3. rostopic pub Roll std_msgs/ Empty --once.

Are there other ways to control the robot?

Trying reading up on ROS to help your understanding. With rosserial, you can have publishers and subscribers on Arduino. You can add sub that takes in data lets say cmd_vel and publish odometry data such as encoders. Whenever you publish to cmd_vel that data will be used by the Arduino.