I often mess around with my quad configuration.   Sometimes I re-flash the firmware which requires the re-calibration of the accelerometer and magnetometer.    To calibrating the accelerometer, the quad has to be on a level surface.  I have a 4-in-1 Quattro ESC mounted to the bottom, which makes an excellent platform to mount to.  After tinkering on TinkerCAD (see what I did there?) for a few minutes, a base was born.  I also had a round bubble level laying around (got it at CDN Tire), which I mounted in the middle.  Pics of the printed unit and quad mounted below.

 

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