IMU 1 and two give you a redundancy on physical IMU failure, but as they are mounted on a seperate board, if something happens to that board, then you loose both IMU’s
So by having one IMU mounted to the FMU board, we eliminate the risk of being left without an IMU.
There are multiple scenarios where this could happen that are a lot more normal than people may think…
For example, if you hit a harmonic frequency of the isolation board, the IMUs could be much worse than the fixed unit… in this case, The third EKF will take over and keep your vehicle safe.
The other thing that it is there for is as a truth indicator.
When you have a log, it’s good to know what is really going on for your airframe.
Vibration is bad for mechanical devices, but if you have no indication of what vibration is really going on, how can you eliminate it?
I hope this gives you an insight into why