The receiver is mounted on the helicopter, receives the pilot's instructions sent by their transmitter and relays it to the servos (or any other piece of equipment that can understand the servo protocol, such as an electronic speed controller or gyro).
There are a number of factors to consider when buying a receiver. These include:
- Number of channels
- Collective pitch helicopters will require at least 5 (usually 6) channels;
- A receiver will only work within it's designated frequency band; either one of the VHF bands (probably 35, 36 or 72MHz), or a 2.4GHz band;
- For VHF equipment, whether the receiver receives the almost-universal PPM protocol, or the manufacturer-specific (but more robust) PCM protocol;
- 2.4GHz transmitters will only work with the same company's receivers; the same with PCM. With PPM, equipment is largely universal, with the main stumbling block being ensuring both transmitter and receiver use positive or negative shift.
- Frequency control
- Most VHF systems control the radio channel used via crystals; both the transmitter and receiver must have appropriate crystals for the same channel. Other users using the same channel locally will cause your aircraft to be shot down. Some VHF systems use an electronic frequency synthesizer to generate any channel within the band without needing crystals. With 2.4GHz systems, the transmitter and receiver negotiate frequencies automatically; however the receiver must first know what transmitter to look for by being bound to it.
When using VHF systems, it is important not to cut the antenna; also avoid coiling up the antenna, as these will both significantly reduce the receiver's range. If you must use a shorter antenna (it can be very hard to stretch it out on a small helicopter), consider a turbo antenna or using 2.4GHz equipment. On larger aircraft the antenna can be strung out and supported by an antenna tube to help prevent damage.
Before first flying your model, you should perform a thorough range check.
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