<p>Controlling dynamical systems, specially high dimensional dynamical networks, is of primary interest. Such a problem is intrinsically related to analyzing the observability of the corresponding state space from measurements, as well as its dual aspect of controllability. An additional constraint can be added by requiring the system to be flat, meaning that its state and actuating signal can be expressed in terms of the measurements and a finite number of its derivatives. Starting from the placement of sensors providing global observability, we address the dual problem of placing the actuators allowing global controllability, and of designing a flat input. Since global observability of a network of <i>y</i>-coupled Rössler systems can be reduced to the observability of each pair of nodes, a step before controlling a network is to design a flat control law for a pair of diffusively <i>y</i>-coupled Rössler systems. It is shown that such a system is flat when a differential delay is inserted.</p>