crystals...lol they are a thing of the past....now things are done on 2.4ghz and the transmitters have to bind to the receiver making it impossible to interfere with other channels...there are apparently millions of combinations and the transmitter randomly picks a frequency to transmit on.............I cant believe that someone did not see the palm sized heli besides the massive petrol car my dad has......that is only one of the 5 he has,also he has 2 helicopters and a quadcopter....and an aeroplane..i also have an electric rc car...