brics_actuator.msg only works with rostopic

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Hello,

I'm fairly new to ROS and the youBot. I'm trying to move Joint 1 of the arm. A notebook is connected via ssh to the youBot. When I use rostopic everything works as expected and the arm moves.

rostopic pub -1 /arm_1/arm_controller/position_command brics_actuator/JointPositions '{positions:[{joint_uri: arm_joint_1, unit: rad, value: 2}]}

ros_graph looks like this:

/rostopic_3016_lotofnumbers -> /arm_1/arm_controller/position_command -> /youbot_driver

Now I tried my own program "ArmVorlage".py, but it isn't moving:

class Goto_Searchposition():
def __init__(self):
    # Give the node a name
    self.node_name = "goto_searchposition"
    # Set rospy to execute a shutdown function when exiting       
    rospy.on_shutdown(self.shutdown)
    self.pub = rospy.Publisher("/arm_1/arm_controller/position_command", brics_actuator.msg.JointPositions)
    rospy.init_node("goto_searchposition")        
    joint_positions = brics_actuator.msg.JointPositions()
    JointValue = brics_actuator.msg.JointValue()
    JointValue.joint_uri='arm_joint_1'
    JointValue.unit = 'rad'
    JointValue.value = 2
    joint_positions.positions.append(JointValue)
    self.pub.publish(joint_positions)
    rospy.sleep(1)
    rospy.loginfo(str(joint_positions))      
def shutdown(self):
    # Always stop the robot when shutting down the node.
    rospy.loginfo("Stopping the robot...")

if __name__ == '__main__':
    Goto_Searchposition()
    rospy.spin()

ros_graph looks like this:

/goto_searchposition -> /arm_1/arm_controller/position_command -> /youbot_driver

The debugging in /youbot_driver looks similiar except the ports are different and these logs are missing when running my own program:

[DEBUG] [1399616158.709991323]: Command for arm1 received

[DEBUG] [1399616158.710137675]: Arm ID is: youbot-manipulator

I would be very grateful if you could help me.

Regards

Timo (I'm sorry i cant post pictures or links cause as a new user i have too little karma)