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So I've been searching around for a 3-axis flight controller for my 450-size helicopter. It seems that nearly every flight controller which is sold today is configured for solely the control of quad/hex/octo-copters, and have little options for helicopters.

Why don't helicopters have much options for flight controllers?

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  • $\begingroup$ Hi tuskiomi, welcome to Drones.SE! What helicopter-specific features do you not see available on multirotor focused flight controllers? AFAIK nothing in hardware is stopping you from using a multirotor flight controller for a helicopter, and the Betaflight firmware supports helicopter configuration. $\endgroup$
    – ifconfig ♦
    Commented Aug 9, 2020 at 3:51
  • $\begingroup$ @ifconfig It's just a generic TREX 450+ clone. AFAIK, multi-rotor PWM outputs will vary highly from heli swash plate outputs, no? $\endgroup$
    – tuskiomi
    Commented Aug 9, 2020 at 4:25
  • $\begingroup$ @ifconfig oh sorry, I read that wrong. I'm not seeing helicopter modes in most controllers $\endgroup$
    – tuskiomi
    Commented Aug 9, 2020 at 4:36
  • $\begingroup$ "multi-rotor PWM outputs will vary highly from heli swash plate outputs, no?" — I don't understand... " I'm not seeing helicopter modes in most controllers" — Betaflight has configurations like "Heli 120" and "Heli 90" among others that I believe should be adequate to describe most common swashplate configurations. $\endgroup$
    – ifconfig ♦
    Commented Aug 9, 2020 at 4:53
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    $\begingroup$ The root issue here seems to be confusion between the hardware and the software. A conventional helicopter doesn't need any sensor a quadrotor FC doesn't have, and it doesn't really need any more outputs, either. It does need a somewhat different set of rules for generating control output however, but that comes down to the software. A fixed-function preflashed quad board won't work, one with suitable open-source software will. $\endgroup$
    – Chris Stratton
    Commented Aug 9, 2020 at 15:26

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Beta flight has helicopter modes ("Heli 120", "Heli 90", etc. depending on your swashplate layout), as does pretty much every other programmable flight controller software.

The outputs from the flight controller are the inputs for the ESCs, which have the same signal protocol as servos. The exception are the flight controllers with integrated ESCs, where the outputs actually drive the motors directly.

This also allows most flight controllers to be used in a fixed wing, where most of the outputs drive servos.

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  • $\begingroup$ Indeed. And even built-in ESCs are easily turned into servo signal outputs with suitable software and either tapping out the gate signal or adding a pull-up resistor and making the software invert the signal... plenty of people have done this to drive brushless ESC's from boards with an integral brushed ESC. $\endgroup$
    – Chris Stratton
    Commented Aug 10, 2020 at 15:24

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