problem of bodyrate controller

[johnwaneboy]

I want to control the UAV in the mode of BODY_RATES.

the related code is as follow:
self.pub_setpoint = rospy.Publisher('/hummingbird/autopilot/control_command_input', ControlCommand, queue_size=10)
aa=ControlCommand()
aa.header.stamp =rospy.Time.now()
aa.expected_execution_time =rospy.Time.now()
aa.control_mode = 2
aa.armed = True
aa.bodyrates.x =pi/12
aa.bodyrates.y =pi/12
aa.bodyrates.z =pi/12
aa.collective_thrust = 3.0
self.pub_setpoint.publish(aa)

And the rate is 50Hz

But the UAV has no response, and still in hover state. So what is the problem?