X8 prop layout and control

I'm considering building an X8.

From what I understand so far, on a given arm, the top and bottom prop rotate in opposite directions - note I'm meaning the props themselves; the motors rotate in the same direction, but the lower motor is upside-down.

If I've got the above right, are all 8 motors controlled individually, or in pairs?  I'd starting thinking in pairs, but now suspect they are 8 individuals as otherwise yaw can't be controlled.

Is that right?

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  • One more question; other than yaw control, and protection against motor failure, is there any other reason why the top- and underside props would need to behave differently?  In other words, other than the above two, can the upper and lower props be fed the same PWM pulse widths to provide pitch, roll and vertical acceleration?

    I'm just wondering whether as an intermediate step, because a X8 should have inherently less yaw, then to start off with I could just attach the 8 ESCs in pairs to the existing 4 PWM connectors. That means I can get going without rewriting chunks of code, and getting new PCBs done.

    As you might have guessed, this is a very DIY project using a Raspberry Pi for all processing, with my own python code, and its own PCB carrying the sensors.  All motion processing is handled in the Pi itself.

  • Thanks - that's exactly what I needed confirming - it does mean I need to think a lot harder about my controller code, and PCB.

    Hugues said:

    The eight motors are controlled individually by their ESC and own PWM signal from the flight controller.

    And indeed the coaxial props on a same arm rotate in opposite direction. Note that the propeller markings must always be UP, even for the props on lower motors.

  • MR60

    The eight motors are controlled individually by their ESC and own PWM signal from the flight controller.

    And indeed the coaxial props on a same arm rotate in opposite direction. Note that the propeller markings must always be UP, even for the props on lower motors.

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