The receiver in the car outputs a pwm or pps? I think its a data telegram that encodes position (servo) and current (speed control). The motors certainly get raw pwm but the servo and esc conventionally converts pps to pwm. Roelof will probably chime in with the format of the telegrams or point you to something. But you may have to overcome the initial response of how practical is this. If its educational its one thing. however you may learn more from buying something and taking it apart and telling us what it does. Once you get to the PWM at the motor you will see its pretty simple. 50% pwm duty is 50% current/voltage or something comparable to half speed. If you want to program something and learn this stuff by reverse engineering some cheap servo and esc you might be able to take what is already there and improve it by creating actual velocity control instead of raw current control. You can get used stuff for nothing and you will wear out the fundamental learning part of this quickly.