For make this project is necessary only a potentiometer connect to 3,3V, GND and A5, see the image below.
For use this example turn the potentiometer all to right and you must see the motor that move to right and a LED that flash.
If you move the potentiometer all to left you must see the motor that move left and a LED that flash.
If you move the potentiometer in the middle position the RC motor is in stop and the LED flash fast.
If the potentiometer is in the middle and you press Blue button you start an automatic test sequence.
For see the messages send by this SW open TeraTerm (terminal emulation) and configure it to: 8N1
This SW whas tested using te Servo Motor MG996R