In this paper, we propose a suite of three schemes for mobile robot coordination and navigation in positionless wireless sensor networks with the help of directional antennas. When a specific node, called waiting-for-rescue (WFR) node, detects the occurrence of an event, it broadcasts an event notification packet to the entire network for asking a mobile robot to come to help. In many existent schemes, the broadcast is achieved by the flooding scheme and thus incurs redundant forwarding packets. We propose an energy efficient broadcast scheme called farthest node forwarding (FNF), which utilizes received signal strength for a node to determine the backoff time to forward the broadcast packet. Thus, farther nodes have shorter backoff times and higher probabilities to forwarding. As we will show, this can reduce a lot of redundant forwarding packets to save energy, while achieving high reachability. The FNF scheme can also help construct a navigation tree which is rooted at the WFR node and contains only packet forwarding nodes. Under the consideration of multiple WFR nodes and multiple mobile robots, we also develop energy- and time-efficient mobile robot coordination and navigation schemes based on the navigation tree for the mobile robot equipped with a directional antenna. The effectiveness of the proposed schemes is verified in simulations by the ns-2 simulator.