Hi guys!
I am working on setting up ArduCopter on my Trex 450 Pro V2 (KX015080AT). After tunning the gains I could fly it on Stabilize mode. But before turning on Loiter mode I decided to check the IMU for any vibration.
I found out there is an intense vibration (-5/+5 m/s/s) on X and Y axis. But what I found most intereting is that X, Y and Z axis vibration are in phase. Check bellow:
Figure1;
After replacing both main rotor and tail rotor shafts I still see the same vibration. I also replaced some torque-tube gears and bearings, but no success. Later, I found out that when the tail rotor blades are removed, the vibration gets really low and not phased anymore.
Figure2;
So, I got new tail rotor blades. Carbon fiber ones, this time. I still get the vibration, but less intense (-3/+3 m/s/s). But at this time, not as in phase as before.
Figure3;
I have tried many different mounting tapes. They all gave me similar results. The APM is positioned just under the main shaft.
I am still not confident to fly like this, since there is a problem that I can’t point out its roots. It looks like to me it is a structural response. To test for that, I disconnected the tail boom braces (those long arms that connect the tail boom and the botton of the fuselage to make the set more rigid). The results are bellow:
Figure4;
I got the vibration frequency a little lower and the intensity a little higher. So, it looks like to me there’s some kind of structure involved in this problem that is being excited at 45deg from the three axis. I could guess it’s the tail boom 
So guys, does anyone ever noticed this on a traditiona heli? Is this normal? Or it is just my 450 that is having this level of vibration at this frequency in all axis? I have no more ideia of what to test. Please anyone help!
Cheers!
Michel Z.
