My transmitter has not arrived yet so I have been trying to get deeper understanding about brushless motor and prop vibrations.
I did not have any success using phone for vibration monitoring so I constructed a stand with two independent sensors:
1) Analog ADXL001-70BEZ
I also made optical blade sensor and counter to be able to trigger scope on full rotation.
In the scope screenshot
yellow - adxl001
blue - piezo
upper digital - optical blade sensor
lower digital - upper digital with counter / 2
When looking in the scope I find it interesting that vibration period is 180 deg of the propeller rotation and not 360 as one would expect. The yellow and blue graphs are quite different but the trend is the same. I would expect if adxl001 signal was put through low pass filter it would look similar to piezo.
If I make prop intentionally way out of balance (screenshot 2) then it does come out in the 360 deg period but if the prop is more or less balanced then the 180 deg period is predominant.
Has anybody done something similar? Do you have more insight as of what is the reason behind this?