The radio control receiver PWM signals are less than 3.3v, so ok for 3.3v microcontrollers.
However pull out GND (ground) it will send 5v or higher. Thus ensure GND is connected first before power.
The problem I had to overcome was to be able to control the robot when it gets into diffculties. The solution was to connect a radio control receiver to the Arduino. If I say one thing, it is connect the Ground of the receiver to the Ground of the Arduino. Otherwise you will pick up additional ghost signals.