The authors propose a new data-gathering mechanism for large-scale wireless sensor networks by introducing mobility into the network. A mobile data collector, for convenience called M-collector is a mobile robot or a vehicle equipped with a powerful transceiver and battery, and it gathers data from Polling Points (PPs) while moving through the field. Single M-collector is suitable for small areas and multiple M-collectors are used for large areas. An M-collector starts the data-gathering tour periodically from the static data sink, polls each sensor while traversing its transmission range, then directly collects data from the sensor in single-hop communications and finally transports the data to the static sink.