I don't have any experience working with this sensor (my disclaimer), however in looking at the source, I did notice two things to check:
- Did you connect your sensor to the SPI pins on the expansion port (the MXP port)? This looks like what the default constructor expects. If you have connected your sensor to the main SPI port on the roboRIO, you may need to change line 117 in ADIS16448_IMU.java.
- When you put your driver station in test mode, do you see the "ADIS16448_IMU" object displayed and does it report angle information?
Finally, you may want to see if there are any error messages or stack trace dumps in the driver station console (or riolog viewer) to help track down where things are going bad.