Trex 700 Y axis vibrations

I’m facing a very high vibrations issue on the Y axis.
My flight controller is Pixhawk 3 Pro.
I have tried to replace blades, tune the blades tracing, replaced tail blades, add FC damping (which make it wars) but it’s stays more or less at the same high values (around 50-60, See XYZ Graph


I’ve tried to check the vibes frequency and I see amplitude of more then 1000 at around 50hz (See Hz Graph).

As far as I understand, the Y is right\left (East\ West) axis, X is Front\Rear (North\ South) axis, is it right?

I’ve added link to the flight log file.

Thank you very much

Sorry to hear that you are having difficulty with this vibration. I assume your rotor speed is 1500 RPM (25 hz). So this vibration is happening twice per revolution (2/rev). I don’t think this is associated with your rotor balance but it could be associated with the rotor track. Or maybe your blade mounting bolts are torqued differently but I’m just guessing there. One thing you could try is to vary the rotor speed by a couple hundred RPM. See if the vibration goes away. if it does then it most likely is your mounting location. The natural oscillation of the structure is being excited by the rotor.

By the way, the X axis is out the nose and the Y axis is out the right side of the aircraft. So accelerations on that axis will be in that direction (i.e x axis accelerations will be fore/aft). For the gyros, roll rate is about the x axis and pitch rate is about the y axis. So the y gyro signal is the pitch rate and the x gyro signal is the roll rate. So your graphs make sense that you have a y acceleration (lateral) and a vibration in roll rate. However the vibration is manifested, it is definitely caused by the rotor. Tough part is figuring how to fix it.

Good luck and let us know what you find out from the rotor speed test

Hello Bill,

Thank you for your respond.

I’ve changed the RPM but still no change.
Tried to play with the blade grips ball link (Blade tracking) and get the vibes lower.
In addition, I replaced the FC damping to 3M foam and get additional improvement (although it just “hiding” the vibrations).
I think that there is a little freedom in the main shaft bearing (although I’ve checked my other hail’s and its looks almost

the same) so I will try to replace them as well.

In the link you can see the last flight log file and pictures of the FC damping with the Velcro (before changing to 3M foam) and with the 3M foam.

What do you think?

Thank you