OctaQuad X8 vs OctaQuad H frame type problems and differences between them

ArduCopter Copter 4.1
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Hi,
I have built two OctaQuad (Co-axial quad) drones with one 18 inch props and another with 22 inch props. The frame design is “H” frame. The firmware is same in both the drones being Arducopter 4.1.5 with frame class OctoQuad and frame type as “H”. I am using CubeOrange with Kore carrier board and all the parameters of Kore carrier board are checked according to the docs.
With 18 inch props, it is flying smoothly but when the same firmware is installed with 22inch props the whole frame is vibrating, more like fluttering of arms. But if the props are changed to 18 inches there is absolutely no fluttering of arms. Another problem is that when frame type “X” is selected, without changing the configuration of motors as front right motor on top is in clockwise direction, then there is no fluttering of arms and no vibrations whatsoever. If the motor configuration is changed according to “X” frame type which is forward top motor is counter-clockwise direction then there is again fluttering and vibrations and if with same motor configuration “H” frame type is selected then there is again fluttering.
The first drone has been performing well with 18 inches prop with “H” frame type and motor configuration done according to “H” type.
According to the wiki the only difference given between the “X” and “H” in OctoQuad is in motor rotation. I have tried reinforcing the frame structure but it is still behaving similar as before. As frame is capable of handling 4 times the load it is intended to maintain.

Below are the pictures for motor configuration in “X8” and “H”:
image
image

Here is the frame:

Screenshot (46)
Screenshot (46)1206×798 68.6 KB

Below is the log file attached which includes both frame type “X” and “H” being selected from frame type selection in Mission Planner. It is configured according to motor spinning direction from “X8” frame type and first given throttle with “H” frame type selected and again armed with “X” type selected:
2022-04-11 17-04-00.bin (909 KB)

What could be the possible reason for the the fluttering when configured with the relating frame class and frame type when used with props higer than 22 inches and why is it working in cross configuration as in when frame type “H” is selected with “X” type motor rotation and vice versa?

1 Like
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Hi, just from the top of my head, for an H frame like yours, select the X frame layout and motor rotation. For an H frame rotated 90° (H lying on its side), the H frame layout and motor rotation would be correct.
The reason for the changed motor rotation between X and H is to use the frame flex to assist yaw control.

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If I am switching to X frame layout and motor rotation then the arms are vibrating, but if I select H frame type in Mission Planner then it stops.

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I think the shaking happened because controlling parameters (PID) for roll and pitch axis are different when you exchanged the axis of between X and H. It can be seen that more weight is distributed along the main arm in your H frame.

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Thanks for the input.
The problem is why is it not vibrating with 18inch props.

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18 inch props will run at a higher rpm. Perhaps the lower rpm of the bigger props hit a resonance frequency of the frame. Did you retune the PID values after changing the props?

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I have checked rotating the bigger props with same RPM as 18inch and there were vibrations.
Yes, I have changed the parameters according to 22inch props and yet there were vibrations.