Pestarini worked on developing the theory of such machines between 1922 and 1930, although he concentrated on their static characteristics, rather than their dynamic characteristics. He contributed three papers on the subject to "Revue Générale de l'Electricité" in 1930, which included some practical applications. The main one was the use of the constant-current output for the control of traction motors on electric vehicles and the operation of cranes, areas in which he had some practical experience, following trials in conjunction with the Alsthom Company in France. In 1930, he made a trip to Britain, and the Metropolitan-Vickers company took his ideas and developed a working system. Unlike Rosenberg's solution, Pestarini, who later became a Professor at the Institute Electrotechnico Nazionale Galileo Ferraris in Turin, connected the additional brushes to an external supply to produce a transformer metadyne. The machine worked as a voltage-to-current amplifier because the flux generated by the current to the load opposed the flux in the control circuit. Development work at Metropolitan-Vickers in the 1930s was led by Arnold Tustin, and the company held the British patents for the Metadyne.