Rtabmap reference frame with ur5 and Kinect v2

Hi all, I've been trying to create a collision map of the surroundings (with rtabmap) for a Universal Robot ur5 using a Microsoft Kinect v2 mounted to an elbow close to the end effector of the robot. I am using ROS Indigo and Ubuntu 14.04. I have written a .launch file that starts up all the nodes. Most of the elements of the algorithm are working fine, except that I don't seem to get the reference frame for the map right.... What do I need to link the map frame to in order to get the mapping in reference to the robot right even when it's moving (I've written a motion_publisher node that makes the robot follow a trajectory for looking around so as to map the whole area around it). This is the .launch file I'm using: With the current configuration (as shown in the .launch file above) the mapping seems to work fine for a while, but after some movements the map seems to loose track... objects are appearing multiple times at different angles from the robot and the map usually shifts to a weird angle from the robot (mostly some sort of an inclined plane to the robots base plane). To me it looks like the transformations aren't calculated correctly. Sure enough I do get "[ERROR] Found empty JointState message" every now and then... not sure where it's coming from and if there's a connection! I am not entirely sure if my setup is correct neither... might just be that I need to connect some frames differently! Unfortunately I'm missing Karma to attach the tf view_frames output... if you upvote my question I'll be able to attach it ;) Any help is very much appreciated, kind of at a loss at the moment. Not sure where to look any further! Thanks all!