Need help setting up an odometry node [closed]

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Here the sitution,I am custom building a robot based around the propellor microcontroller. i have already set up a node to send and receive data from it via the usb cable and a another node that takes the compass and odometry readings from the propeller, calculates the x,y values and then puts them into a transform. However I cannot figure out how to access the individual values so I can send to the navigation stack via my odometry node. keep in mind that I am relatively new to ROS and would prefer to do as much as the programming in python.