Frame Vibrations Theory

I read a post not so long ago by @Leonardthall trying to solve a problem with auto tuning.
He was saying that a lot of vibrations or flexes in the frame are caused when the props push air against the top side of the arm or frame.
If the props were to be mounted on the underside of the arm, would this negate or at least severely reduce the problem, or would incur other problems.

Just thinking aloud. I have no experience with drones myself, and have no drones to experiment

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I have exactly the same thought, glad you typed it out and posted it.

As long as the centre of gravity is below the prop plane, I see no reason why it would not be beneficial.
My lack of experience may prove me wrong yet though.

Has anyone tried this? I have a Tarot X6 with high vibrations I need to fix somehow. I might try this. I have two 10,000mah batteries on top I’ll probably need to place underneath.

The CG does not have to be below the prop plane. I have a multirotor where its well above the prop plane and it’s no problem. One of my better performing craft actually.

  • Are your propellers balanced?
  • Are all your motor bearings lubricated (eg: INOX)s ?
    INOX MX3
  • Are all your motors fixation screws secure ? did you use green loctite?
    Green loctite
  • Are all your mounting arms device on the frame solidely secured?
    If all the above correct (which I doubt) you could try to fill up all your hollow tubes with this:
    Foam to fillup multirotor hollow carbon tubes

Hope you’ll find your source of vibrations.

Props are well balanced T-Motor carbon fiber 18 inch. Motors are new T-Motor MN501’s, which I assume are lubricated, but I’ll buy some of that lubricant you mentioned. I used Locktite on all the screws and everything feels solid. The X and Y vibrations are very minimal, it’s the Z vibrations that are the problem. My thought is there might be a slight pressure increase as the props pass over the motor arms causing the props to flex slightly many times per second causing the Z vibration? Mounting the motors upside down, so the arms are on the intake side of the props, I’m thinking might help. I’m wondering if anyone else has tried this.

As far as I can see it, the prop passing the frame will cause a vibration either way. Above, it causes a positive pressure spike and below it causes a negative pressure spike. The only way I can see to mitigate this would be some combination of maximising the distance, minimising the cross-sectional area with respect to the air flow and using an ‘aerodynamic’ profile for the arm.