Pixhawk 2.1 Hard Mount Recommended?

#1

Hello,

I’m having some vibration issues with my build using the Cube. The PX4 documentation provides the general recommendation of using vibration-isolation when mounting the FC, which I was about to try. However, today I saw a Facebook thread where ProfiCNC says that the Cube should always be hard-mounted with screws, and that soft-mounting can be dangerous.

I asked them what should I do about my vibrations, and they said I should use the Chibios version of Ardupilot instead, which can handle the vibrations, as long as the vibrations are not so high that they cause data clipping, and reiterated that soft-mounting, even with double-sided foam tape is not a good idea.

So I’m not sure what I should do here. I would like to stay with PX4 because I’m much more familiar with it than Ardupilot, but now I’m worried that vibration-isolation may be dangerous. If I don’t use vibration isolation, it seems like I would not be able to use PX4, because fiddling with the filtering seems to be discouraged by the documentation.

From what ProfiCNC says, Ardupilot seems better suited for the Cube, especially when on high vibrations. Is this true? Any suggestions on what I should do? Could soft-mounting the FC be dangerous?

Thanks

Part of the chat:
ProfiCNC - “The Cube should be HARD MOUNTED!!! Use full rate logging on the three IMU’s then do an FFT on the data. This will give you an idea if your frame has any special requirements. Without doing this step, adding any form of external isolation is most likely unnecessary at best, and most likely dangerous. Unless all three IMU’s are clipping during all phases of flight, it is highly unlikely that additional isolation will be required. Ensure you are using Chibios, EKF3, and all three IMU’s are enabled”

Me - “May I ask why it can be dangerous to mount the FC with a foam such as this one? Thanks”

ProfiCNC - “Because the internal vibration isolation works correctly. Adding this makes the system floppy.”

#2

The cube 2.1 should only be hard-mounted.
If your build suffers from vibrations, check first that props are properly balanced, no resonance frequency etc occurs.
There is no difference between Nuttx or the Chibios kernel when it comes to vibration. Also, EKF2 is fully sufficient, EKF3 gives you no benefit here.

#3

Just for correctness, there actually is a difference between ArduPilot on nuttx v ChibiOS in how well the estimators can collectively handle vibration, as under ChibiOS you can run more ekf cores without scheduling issues. Beyond that, I don’t think here is the right place to discuss it.