This article focuses on the utilization of a mobile robot as data mule for collecting and transferring data from a ground wireless sensor system (WSN). For the case, where the nodes' communication is impeded either due to a non-connected node, or due to excessive retransmissions caused by significant packet losses, the effective transmission rate is reduced and the energy consumption for the RF-communication increases. In this case, the mobile element/robot approaches the nodes and collects data with a reduced packet loss rate resulted from the use of the proposed technique. The devised algorithm is implemented in the operating system Contiki. Then, the mobile element transfers the stored data to the desired destination. In the adopted scenario, the mobile element assumes prior knowledge of the nodes' locations and its trajectory is extracted by solving a combinatorial optimization problem that resembles that of Traveling Salesman Subset-tour Problem (TSSP). Furthermore, the system is capable of transferring large volumes of data between source nodes and destination one, taking into account: a) the reliable data transmission, b) the traveling distances between the static nodes, c) the visiting/service time at each node and, d) the energy consumption of the mobile robot. Finally, experimental studies indicate the efficiency in terms of reliable data transmission and transmission time among pairs of static and a mobile node. Subsequently, the effectiveness of the overall concept is validated by means of simulations.