I'm using the MPU-9250 on a custom PCB. Communication is done via SPI in FPGA logic. The gyro full scale is set to +/- 250 dps. Changing the full scale scales z, x and y data equivalently as expected. Default register values and registers with constant values like WHO_AM_I (0x75) read back expected values. I can also write registers and read back the same value that I wrote so I'm confident the SPI interface is working.
With my MPU-9250 on the table, all I have to do is tap the table near the device in order to see activity on the x and y axes. This tapping does not cause any signal changes above the noise floor of the z axis. I have to pick up my device and flick it pretty hard back and forth (around z axis) in order to see z axis signals rise above the noise floor. It's easy for me to cause the x and y axis signals to range up and down through their whole range by gently rotating the device but the z-axis response is so small, even with a really hard flick, the signals only span a very small percentage of the range. When the MPU-9250 is at rest, the noise on x and y is similar. At rest, the noise on the z-axis is slightly larger than x and y.
Has anyone else encountered this? Any ideas what could cause this?
Thanks,
Jim