Building your own Multicopter can bring a fountain of entertainment and enjoyment. However, flight controllers and transmitters are full of geeky acronyms that create turbulence of confusion. Electronics have evolved past the simple frequencies of the RC car days to one where each brand and even model sometimes uses its own unique protocol. This article will cover the most common radio communication (RC) protocols in quad building and briefly, elaborate on each one.
What is an RC protocol?
It is the language your transmitter sends to the FC (flight controller) in your multicopter, unless they speak the same language they will not operate or even connect together. This can catch out beginners who purchase an advanced transmitter than a quad separately only find out the transmitter is not compatible with their receiver.
PWM
PWM which stands for pulse width modulation is one of the most utilized protocols for RC. In the classic days RC fixed airplanes were the only flying machines, receivers were used to manage servos or even ESL straight with a PWM signal. Nowadays PWM receivers are still in widespread utilization partly due to their low cost and also due to their historical use. As the name suggests the exact length of the signal pulse can vary (usually from a minimum of 1,000 to 2,000 microseconds).
CPPM
The CPPM protocol is a series of PWM signals, which are relayed one after the other on a single cable. But unlike PWM, CPPM signals are modulated in a markedly different manner. CPPM happens to be an analog signal time domain. This just means the signals can be sent one after the other, but never at the same moment. This makes PWM technology less precise and is characterized with more jitters than serial communication protocols. The major advantage of the CPPM protocol is the fact that only a single cable wire is necessary to be able to serve several channels making the wiring connection easy and simple. CPPM can usually handle a maximum of eight channels effectively.
SBUS
This one of the serial RC communications that is exclusively used for the brands FrSky and Futaba. SBUS can cater for a maximum of eighteen channels while making use of a single signal cable. Nevertheless, it is important to point out that it is an inverted UART signal. Most flight controllers can easily decipher UART inputs but find it extremely hard to support the inverted varieties. This protocol was started by Futaba and is protected by patents, so you won’t see others using it, a great marketing idea to keep you locked into the brand, they do make some amazing transmitters tho so it might not be a bad thing.
DSM (DSM2 & DSMX)
The DSM protocol comprises of the DSM2 and DSMX protocols. It is primarily utilized for 2.4 GHz Spektrum RC transmitters as well as receivers. DSM protocols are infinitely lesser susceptible to noise, the presence of other transmitters that may be using a similar frequency, and even interference. The DSM2 protocol in particular also possesses a backup frequency at startup to anticipate a scenario where the primary signal may fail. Both these RC protocols are virtually the same, and the only difference lies in the exact criteria they make use of to jump between different channels
Spektrum Satellite
Spektrum Satellite has an extra antenna that is in direct connection with the main receiver. It is, for the most part, meant to enhance link dependability by offering diversified reception, similar to those WiFi routers with multiple antennae sticking out.
FlySky IBUS
IBUS is the very latest serial protocol. Typically, it is basically a two-way RC communication systems. One of its ports has been specially designed to handle servo data input. While the other facilitates for efficient connection with sensors.
PCM
PCM stands for pulse code modulation, and is somewhat similar to PPM, with the main difference that it is digital while the latter is analog. PCM has the capacity of detecting signals and even error correction. It is also less prone to interference and dropouts compared to the analog PPM.
How to choose the right protocol
If you are buying a prebuilt RTF, don’t worry too much as the standard controllers often don’t disclose what protocol they use and are difficult to connect to other transmitters. Instead, enjoy the simplicity of a pre-setup quad.
If you are building your own from scratch, decide first what transmitter you like and then find its compatible protocols, and make sure you get a receiver using the same protocol. The DEVO’s are our popular transmitters.
What if I have mismatching protocols?
There is a range of protocol converter boxes that you can use to convert mismatching protocols, and this allows your nice transmitter to pair with various multicopters. A converter box is usually installed in the multicopter and needs to be wired into the existing system. Our range of SBUS adapters are here, but check Google for more specific ones as we don’t have the full range.
You could also totally rewire the setup and install a direct replacement receiver, in either case, it is better for your pocket and your setup to avoid the issue and check protocols before grabbing the goods.
If you have any questions or comments, please contribute as this is by no means an expert analysis of the protocols, just a general background overview.
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