Proposes an architecture for tightly coupled multi-robot coordination that is well suited to cooperative manipulation tasks. At all times, a robot is identified as a leader, while the others are designated as followers. The assignment of roles and the coordination between the robots is guaranteed by communication protocols and control algorithms. The key feature is the flexibility that allows changes in leadership and assignment of roles during the execution of a task. We describe the experimental implementation and demonstration in a cooperative transportation task, in which two and three heterogeneous robots cooperate to carry a large object in an environment containing obstacles.