One solution came in mind for RC car steering. Control servo (planned or RC car steering) with potentiometer. Testing setup is very simple. Servo setup: +, – and control pin. Same as here: Simple servo setup Potentiometer will work as voltage divider. Here is more info about it: Voltage divider.
One day thought that would be nice to make a RC car controlled with arduino. Unfortunately I don’t know how make such hardware, I needed to to find any car, that has possibility to turn front wheels to both sides. After few days of searching (all of them were expensive or front wheels were “fixed” they were able only to rotate clock or co-clock wise) found this: