docs: def connect(self):
          '''
          Connect to the drone.
  
          :raises RuntimeError: if the drone is connected or closed already.
          '''
          if self.connected:
              raise RuntimeError(
                  '{} is connected already'.format(self.__class__.__name__))
          if self.closed:
              raise RuntimeError(
                  '{} is closed already'.format(self.__class__.__name__))
          self.connected = True
          self._connect()