Bio-inspiration can lead to a significant improvement in propulsive efficiency and maneuverability of Autonomous Underwater Vehicles employed in large areas exploration. As a matter of fact, fish swimming capabilities are still far superior to what has been achieved by the modern nautical technology. In order to exploit the propulsive principles of fish swimming, a novel mechanism has been designed and prototyped to drive the thrust-generating caudal fin of the biomimetic underwater robot manufactured by the authors.