code: def take_off(self, height=DEFAULT, velocity=DEFAULT):
          
          if self._is_flying:
              raise Exception('Already flying')
  
          if not self._cf.is_connected():
              raise Exception('Crazyflie is not connected')
  
          self._is_flying = True
          self._reset_position_estimator()
          self._activate_controller()
          self._activate_high_level_commander()
          self._hl_commander = self._cf.high_level_commander
  
          height = self._height(height)
  
          duration_s = height / self._velocity(velocity)
          self._hl_commander.takeoff(height, duration_s)
          time.sleep(duration_s)
          self._z = height
docs: Takes off, that is starts the motors, goes straight up and hovers.
          Do not call this function if you use the with keyword. Take off is
          done automatically when the context is created.
  
          :param height: the height (meters) to hover at. None uses the default
                         height set when constructed.
          :param velocity: the velocity (meters/second) when taking off
          :return: