When speaking about radio systems for remote controlled models, multirotor, airplanes, gliders, there are some shortcuts that might be unknown for beginners. Those are: PWM, PPM, Serial RX, S.Bus. Today I will explain basic concepts behind them, and when they are used.
PWM, as Pulse Width Modulation, is something a standard for controlling different devices onboard remote controlled model. Almost all servos, ESC, flight controllers and radio receivers can work with PWM signal. There might be some exceptions, but they are so rare, that we can skip them.
Stick (switch, POT) position in PWM signal is encoded as length of signal. Signal that lasts 1000us encodes minimum stick position, and signal of 2000us encodes maximum stick position.
In PWM, each channel is available as separate port of 3 pins (Ground, +5V, Signal). So, if receiver has 8 channels in PWM mode, that means that it has at least 8 ports of 3 pins. 24 pins, 24 cables, lots of mess. And this was great for airplanes, where each control surface is controlled by separate servo connected directly to the receiver. But is not so great for quadcopters and event airplanes with flight controller. Not only it requires a lot of cables, but also complicates things on flight controller’s end. It requires an interrupt for each channel, takes a lot of space and to be honest, it’s completely not needed. Why? Because we have something better…
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