It flexes in flight (under power load, especially with a battery). The BeagleBone quadcopter we built with plexiglass flexed noticeably. FR4 is better, but it still will flex.
Fr4 material is basically fiberglass, and at 1.6mm thick it doesn't take much to bend it if it isn't supported. I think the weight of the motors could be an issue.
While flying, the whole thing is suspended by the motors. It'd only be the weight of the centre components (mostly battery) that'd be flexing the arms.
(While crashing, all bets are off. But way back when I used to fly RC gliders they had a saying "If you build them to crash, they won't fly well. If you build them to fly well, they won't crash.")
Also, it's not like anyone expects thousands of hours of flight worthiness out of a consumer or even semi-pro drone. Sure the military might spec that for their Predator replacement, but most drone hobbyists I know end up with a bunch of perfectly serviceable old drones which they no longer fly because their gear became obsolete well before the mechanics failed irrepariably.
Thanks! this could be a great idea,the 2mm PCB could be an interesting option! We are devoted to 1.6mm PCB since the 5" version that weighs 220g and we haven't had any broken or issue on the PCB piece. The battery is well attached, fixed in 6 well distributed points on the PCB and aligned perfectly in the center of the 4 motors.
Till 1 year ago it has been a great concern, especially for small drone. Now thanks to andyp1per, new Ardupilot dev, we have amazing results with dynamic filtering gyroscope noise, we could even track the mechanical noise peak based on actual RPM or live FFT.
You have to consider under the selected IMU, in the center, there is the most of the mass, made by the single 18650 Li-Ion battery. This solution is working, ArduBee is already flying good with the low pass filter in the gyro sets at 110Hz, if vibration would be an issue I guess it cannot fly
