I custom designed this 6" ultralight quad frame. The first test flight showed a lot of “Compass or GPS error” messages in the screen display. After the flight I checked the compass logs (Raw MagX/Y/Z range normal, XKF4.SM, CompassMotor interference below 12%). I noticed the log showed vibes are very high, 17.5m/s² during hover, spiking to 75m/s² during flight.
I took a closer look at the air frame and found it to be rigid, even compared to my race quad. But tapping the ends of the arms creates a pure sounding and prolonged ring like a tuning fork.
To diagnose further, I removed all the booms (GPS, camera gimbal, antenna) and fitted some gasket paper either side of the arms where they clamp to the frame. This halved the vibes on X and Z axis but not Y.
I compared the frame again to my old quads. I can see that my old quads have “slip” in the arm joints. One of them, if I twist it, I can feel the plates slip over each other, very sloppy, but has a lot of damping. Whereas my problematic quad has very rigid assembly. Each arm breaks out into two legs, has three screws spaced far apart and zero slip.
So I’m wondering if I’ve made the joints too rigid? Do I need to reduce the rigidity? Maybe decrease the distance between the screws and use only two screws per arm?
Any suggestions welcome.
