Other things to think about when purchasing a helicopter system are the servos and the battery pack. It is desirable to choose servos that have output shafts that are ball bearing supported. Since the pressure and vibration on the servos in a helicopter is usually greater than in a plane, bushing servos tend to wear out very quickly and lose their precision which is extremely important in the controlling of a helicopter. Because you are using a minimum of five servos and a gyro (to be discussed later) in a helicopter, and the higher frequency of control input, it is very desirable to have a larger battery pack than the standard 600 maH pack that comes with most aircraft radios. A pack in the range of 1000 to 1200 maH is a better pack to consider. Many helicopter radios take both of these concerns into consideration and come packaged with five BB servos and a large batter pack.
Also, it is recommended to get a computerized radio so that it will be easier to setup your helicopter for the correct pitch and throttle settings. Non-computerized radios can also be used, but they tend to be limited in its function and you will very quickly outgrow them once you get into flying aerobatics.

Receiver

You will also need a receiver to receive the transmitter signal and then transmit it over to the servos. There are basically two types of receiver. But getting whichever depends greatly on your type of radio and what it can support.

PCM
The PCM receiver is a digital receiver that uses normal FM Frequency, but the signal is an encoded digital signal in which the PCM receiver interprets it as commands. Since the signal is digital, if there are any interference or the signal is poor, the PCM receiver can be programmed to go into a fail-safe mode. In this mode, the servos will move to a pre-programmed position until the signal comes back.

PPM
PPM receivers are the "standard" type of receiver for most radios. Glitches in signal are immediately noticed by erratic movements of the servos.

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