Hi, I was following the tutorials on learn.turtlebot.com. Everything has been fine until I started the section Create a Map Via Teleoperation (http://learn.turtlebot.com/2015/02/01/11/). I was asked to run: roslaunch turtlebotbringup minimal.launch, which turned out OK, and run: roslaunch turtlebotnavigation gmapping_demo.launch, which the above error message start popping up: No devices connected.... waiting for devices to be connected. Can anyone help solve this issue? Thanks!

[ INFO] [1458733466.373439221]: Initializing nodelet with 4 worker threads. [ INFO] [1458733467.718515305]: No devices connected.... waiting for devices to be connected [ INFO] [1458733470.718925198]: No devices connected.... waiting for devices to be connected