def __init__(self, parent=None):
     super(CliffSensorFrame, self).__init__(parent)
     self._ui = Ui_cliff_sensor_frame()
     self._motion = TravelForward('/mobile_base/commands/velocity', '/odom',
                                  '/mobile_base/events/cliff')
     self._motion_thread = None
     self._distance = 1.2
     self._state = CliffSensorFrame.STATE_FORWARD
     self._is_alive = False  # Used to indicate whether the frame is alive or not (see hibernate/restore methods)