H-frame motor layout

ArduPlane VTOL Plane
1

Hi,

I’m building a Skyhunter 1800 conversion to a quadplane (4+1) but I can’t find a layout diagram for the H configuration. The docs only say:

https://ardupilot.org/plane/docs/quadplane-frame-setup.html

  • Output 5: Front right motor, counter-clockwise
  • Output 6: Rear left motor, counter-clockwise
  • Output 7: Front left motor, clockwise
  • Output 8: Rear right motor, clockwise

You can remember the clockwise/counter-clockwise rule by “motors turn in towards the fuselage”, except for the H configuration, there all directions are inverted!

So does it mean that it will be for H as follows?

  • Output 5: Front right motor, CW
  • Output 6: Rear left motor, CW
  • Output 7: Front left motor, CCW
  • Output 8: Rear right motor, CCW

After assembling, the wing section is quite flexible. I’m considering some fiberglass laminate, but how much flexibility is more or less acceptable? (I know that it’s not very precise). The arms have very good precision with respect to the left-right movements, but are flexible when it comes to up-down movements (because the wing twists).

2

For a quadplane, motor arms on the wing uses X configuration. Motor arms fixed to the fuselage uses H configuration.

3

But the docs say:

In general, in a Quad configuration, use H mixing and not X mixing, independent of the actual physical mounting arrangement.

https://ardupilot.org/plane/docs/quadplane-tips.html

4

The docs describe the effects of flexing right, but then the wrong conclusions are drawn.
With the motors mounted to the wings, x-config, left yaw input causes the left front and rear right motor to throttle up. With the inevitable flex, this causes the left motor arm to pitch up and the right motor arm to pitch down. This leads to a small amount of thrust vectoring. Thrust forward on the left side, thrust to the rear on the right side, aiding the yaw movement. The H-config would counteract the yaw torque in this situation or even override it.
The same goes for fuselage mounted motor arms, but with left/right thrust “vectoring”, not front/rear.

5

Thanks for the answer, I can’t say that I understand all of it but I’ll begin with the X config. I’ve added some plywood to the bottom of the wings and the flexing now isn’t much worse than in my carbon-frame octocopters.