xcraft:
I do not want a arduino in the car, i just want to use arduino in the RC transmitter.
If you are hoping to do this without any feedback about where the car is, what you're trying to create is effectively a DIY version of Bigtrak. Perhaps you would be better off simply buying one. If you do go ahead with the DIY version then the most sensible design is to put the Arduino in the car and make it autonomous (the Arduino controls the servos and motors directly) with no radio involved at all.
If you really want to have the Arduino control the servos and motors via the original radio link then you need to understand what type of radio you have got and either replace the joystick pots with digital pots or build your own Arduino-controlled radio transmitter. Neither of these are things that I'd expect a novice to do successfully.
How much time and money did you expect to spend on this? Do you have any practical electrical/electronic/programming skills?