Can't enable/add camera on Kuka Youbot in ROS indigo?

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Hi I am fairly new to gazebo and ROS indigo. I want to add a camera on the Youbot so that I can track road lanes and do lane keeping which I'm doing for a senior design project. So first I installed the youBot Gazebo package for ROS indigo which i got from the youbot store website: http://www.youbot-store.com/wiki/inde...

Now its seems that the youBot package already came with several cameras including the Asus Xtion camera, Kinect camera, and the Microsoft Lifecam with their gazebo.xacro and urdf.xacro files located under the youbot_description/urdf/sensors folder. So I tried to enable the Microsoft Lifecam sensor by opening the youbot.urdf.xacro file located under youbot_description/robots folder and added this line:

I also copied and pasted the simulation tags from the bottom of the microsoft_lifecam.urdf.xacro file:

and pasted it near at the bottom of the youbot.urdf.xacro file and modified it to this:

After that, I run the simulation. I run the simulation by typing roscore at the terminal. Then I open a new terminal and type roslaunch youbot_gazebo_robot youbot.launch and wait for Gazebo to load. But when Gazebo opens up, the Microsoft Lifecam camera doesn't appear anywhere on the Youbot. I have tried to do the same procedure for all three cameras but none of them appear on the Youbot when I run it on the Gazebo. I know I'm doing something wrong, but not sure how to fix. If someone could help me with this issue so that I can simulate a camera on the YouBot, I would appreciate it a lot. Thanks.