The vibration problem

If you want a steady quadcopter (or multi-copter), you need an accurate reading of angles (pitch and roll).

The reading is made through a combination of calculous (which I find really hard to understand) that mixes the information of a 3-axis accelerometer, 3-axis gyroscope and a 3-axis magnetometer.
When you have 4 motors spinning at 10,000 RPM each anywhere near your inertial sensor, you will probably sense all the vibration. I can bet you will.

When the vibration is very hard, no software correction or filter is possible. So a mechanical solution is needed.

This is how we solved the problem:

IMU anti-vibration mount

The IMU (9 DOF) is attached on an independent board, which is "floating" on rubber mounts. This absorbs most of the vibration generated by the motors, and the rest of the vibration is filtered out by software.