Hi, I'm trying to do the same thing - I'm trying to combine the wiimote IMU
data with visual odometry from the vslam package.  I've tried all the
troubleshooting tips and I still can't figure out.  As Alessio mentioned, I
had to remap imu_data to imu/data in the robot_pose_ekf package.  Here's my
output when I run the script wtf.py in the robot_pose_ekf package.

 * Odometry sensor
   - is NOT active
   - received 0 messages
   - listens to topic 
 * IMU sensor
   - is NOT active
   - received 1569 messages
   - listens to topic /imu/data
 * Visual Odometry sensor
   - is NOT active
   - received 62 messages
   - listens to topic /vo
Output:
 * Robot pose ekf filter
   - is active
   - sent 20 messages
   - pulishes on topics /robot_pose_ekf/odom_combined and /tf

Note that even though messages are being received (constantly on imu and
less frequently on vo), the sensors are inactive, but the filter is
active??!  Also, I am receiving messages on /vo, imu/data and
/robot_pose_ekf/odom_combined as checked by rostopic echo, however the
transform between odom_combined and base_footprint is not being published.
rosrun tf tf_monitor tells me that robot_pose_ekf is a broadcaster, but it's
not publishing any transforms (odom_combined) in the list of frames. 
rostopic echo /robot_pose_ekf/odom_combined gives me:

 header: 
  seq: 23
  stamp: 
    secs: 1297559471
    nsecs: 703006000
  frame_id: odom
pose: 
  pose: 
    position: 
      x: -0.0384588956181
      y: 1.53740890261
      z: -0.412322561686
    orientation: 
      x: 0.247238159565
      y: -0.634830219515
      z: 0.297771354173
      w: 0.668727228008
  covariance: [15823.031743707601, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
15823.031743707601, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 15823.031743707601, 0.0,
0.0, 0.0, 0.0, 0.0, 0.0, 15823.031743707601, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
15823.031743707601, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 15823.031743707601]

What's going on here? Why are my sensors inactive and why isn't my required
transform being published?

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