Hi,
the main cause for vibration are the gearboxes, shape and cut and speed of the gears's teeth, and how they engage/interact, particularly under high load.
Then, long comes nothing, then the drive system (motor/engine with mounted accessories).
Then, it makes a difference if the mechanics/airfraime/rotor head construction can dampen that vibration, and to which degree, and what—as a result—reaches the sensors, and on which axis.
As an example, take any 200-250 size heli (or even 450/470) with normal layout, and with their respective ridiculous head speeds.
They vibrate anything kaputt, sooner or later, and they mess especially with the accelerometers.
Take the LOGO 200 as an example of a direct drive model, no gears but servo gears. The vibration level is 'suddenly' well within the range the sensors there can handle, and even at similarly ridiculous head speeds of up to 7,000 1/min.
The data indeed does not provide much information for general improvement, but being able to see the loads on the sensors is a well-appreciated eye-opener ("MY helicopter has NO vibration, I have YEARS of EXPERIENCE!" :-), as well as a tool to compare changes.
—Eddi
Born to fly ...
forced to work.