Dynamixel motors not found

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I'm going through this tutorial about connecting/ running Dynamixel servos through ROS (these are AX-12 servos). In step 3.Step 2: Create a launch file for the manager node, I created a .launch file as instructed by copy-pasting the supplied code in to a new file named controller_manager.launch. After executing the command "roslaunch dynamixel_tutorials controller_manager.launch", I receive an error. The error states [FATAL] [WAllTime: 13151009139.949289] pan_tilt_port: No motors found

The error log file referenced states the same information, the motors can not be "pinged" and therefore the process is killed.

Running the command ls -la /dev/ttyUSB*

Gives me crw-rw-r-- 1 turtlebot 188, 0 Oct 23 11:18 /dev/ttyUSB0

lsusb gives me Bus 002 Device 003: ID 0403:6001 Future Technology Devices...

So it looks like the computer "sees" the USB connector. I've even tried a different motor and different power supply...

Any ideas?