Fatal - pan_tilt_port: No motors found

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Hello Everyone, I'm following the tutorial dynamixel_controllers/Tutorials/ConnectingToDynamixelBus and I cannot found my motor AX12+. I'm testing just one AX12+ on Linux 12.04 and 13.04 and both do not work.

My ls -la /dev/ttyUSB output is:

crw-rw-rw- 1 root dialout 188, 0  1월 11 16:52 /dev/ttyUSB0

When I ran the roslaunch command my last lines before the error are:

setting /run_id to 4e5d5690-7a95-11e3-bc0f-e0cb4e79fce2
process[rosout-1]: started with pid [28760]
started core service [/rosout]
process[dynamixel_manager-2]: started with pid [28772]
[INFO] [WallTime: 1389426744.355062] pan_tilt_port: Pinging motor IDs 1 through 25...
[FATAL] [WallTime: 1389426746.482201] pan_tilt_port: No motors found.

I already tried with 3 different AX12+ motors and always the same error. I'm using a 9V power supply and seems perfectly working, the motor blink once when the power source is connected.

Thank you very much for the attention.