Filter for noisy accelerometer data I tried to read up and get a filter for a 3-axis accelerometer but this is more confusing than I thought.
I have an IMU with a 3-axis accelerometer on the end of a robot link which is rotated  around on one axis.
When at rest with just gravity acting on it I get these readings:


Now the band of the data is kinda broad and very noisy . I thought that at first I could maybe look at the frequency spectrum and cut out unwanted frequencies but honestly the FFT doesn't tell me anything I could remove. What does initial spike in the spectrum mean and and how would I put a high or low pass filter over the data if it looks like such a mess? Do I need to smooth it in some way?
Preferable I would want a nice arc of the data which follows the movement of the end of the arm but I don't know how to achieve that. Could it be that the arm movement by the motor introduces too much noise?
Thanks for any help!
Most accelerometers suffer from bias --- a non-zero, constant rest measurement. See, for example, this page. 


  A further imperfection is called zero g bias level, or offset. This is the reading the sensor provides with no acceleration, and, unfortunately, that is rarely zero (in the Z direction it should be 1 g). In fact, the error can be substantial, frequently hundreds of times larger than the device’s resolution.


So you need to remove this DC offset (which is how the bias appears) from all your measurements.  If you need to know the $g$ value from the $z$ accelerometer, you will need to calibrate it first in the $x$ or $y$ plane (to remove the effect of gravity).

Have a read through this answer to another question, and try applying a DC blocker to your data.