def cmd_velocity(self, args):
        '''velocity x-ms y-ms z-ms'''
        if (len(args) != 3):
            print("Usage: velocity x y z (m/s)")
            return

        if (len(args) == 3):
            x_mps = float(args[0])
            y_mps = float(args[1])
            z_mps = float(args[2])
            #print("x:%f, y:%f, z:%f" % (x_mps, y_mps, z_mps))

            self.master.mav.set_position_target_local_ned_send(
                0,       # time_boot_ms (not used)
                0, 0,    # target system, target component
                mavutil.mavlink.MAV_FRAME_LOCAL_NED, # frame
                0b0000111111000111, # type_mask (only speeds enabled)
                0, 0, 0, # x, y, z positions (not used)
                x_mps, y_mps, -z_mps, # x, y, z velocity in m/s
                0, 0, 0, # x, y, z acceleration (not supported yet, ignored in GCS_Mavlink)
                0, 0)
velocity x-ms y-ms z-ms