That is because there isn’t one. The Rpi 4B 4GB is running a modified version of Donkey Car 4.1.0, using an Intel T265 tracking camera for path following, and communicates with a PCA9685 servo driver module that provides steering and throttle PWM signals to a Dimension Engineering Sabertooth 2X10 RC motor controller operating in the differential drive mode. The two 12 vdc motors do not have encoder feedback.