Why acc.z is equal to +1g not -1g

[lyah]

Hi everyone,

I am wondering why the accelerometer sensor reading acc.z is equal to +1g not -1g when crazyflie 2.0 is stationary on the ground? Because the gravity is pointing downwards and the sensor is not installed upside-down, I think the acc.z should be -1g instead of +1g.

I move the robot upward to accelerate it, and the acc.z increases which mean the positive direction of accelerometer sensor is pointing upward which is the oppose direction of gravity. So it is really strange that acc.z is equal to +1g. I also check the code, and it seems that there is no place in the signal processing code that acc.z reading is flipped.

Thank you. Appreciate the help.

[lyah]

Just figure it out why. This is a stupid question after studying the working principle of the mems accelerometer. http://mafija.fmf.uni-lj.si/seminar/fil ... koncna.pdf

Because of the gravity, the mems sensor has a stationary deformation which is equal to the support force which has different direction with gravity.