To satisfy the requirements of independent navigation in low cost multiple robots, a navigation frame of masterslave robots with only one master robot is introduced briefly. A range-only navigation algorithm for slave robots of low cost is presented for the navigation in unknown current. This algorithm only needs a master robot. The master is just a single mobile node which has high navigation performance. Observability of this master-salve system is theoretically analyzed. The conditions of slave robot trajectory under which observability is guaranteed are evaluated by a slave robot in real-time. The slave takes appropriate action to control its heading to achieve observability if observability is lost on the current trajectory. The navigation algorithm is implemented by a standard extended Kalman filter, and it is able to acquire accurate estimation of robot's position. The simulation results show its effectiveness of the proposed algorithm.