how can i hack remote control of rc helecopter?

cHi , i need to control one of sticks (throttle) ,i used switch which chose arduino connected to channel or sticks connected to channel ,  i send pwm otput from arduino then  i used smoth circuit to make it true analog then  i connected it to switch but nothing happen at motors ,what is possible type of data voltage that sticks give so i can replace it by arduino voltage , how can i know voltage if  havent datasheets?
il

The stick is a variable resistor. It's connected through a reference resistor creating a voltage divider. There is a mico controller on the controller that reads the voltage through this voltage divider.You need to do a little more then plugging in the contacts of the variable resistor to the ground and analog pins of the Arduino. You should go directly to the contact on the micro controller that read that resistor. Gotta make sure that the controller and the Arduino share a ground connection otherwise it won't work.