DC machines - Constitution and operation

The DC motor class includes only motors with DC-powered commutators. It excludes series-excited AC motors, known as universal motors, which use the same commutator structure, as well as "brushless" structures, where the commutator becomes electronic.

The commutator motor was the first electric machine to be invented. History records the name of Zenobe Gramme for its first industrial realization in 1871. Shortly afterwards, Wernher von Siemens proposed the cylindrical armature version of this machine. These two machines, conceived as an application of field theory, only operated as generators at the time. They brought smiles to many faces when confronted with the power of steam. But their rapid application as a reversible motor made them a great success, and by 1880, mine trains were electrified and the first electric elevator was built. By the turn of the century, electric traction had earned its spurs, with several record speeds of 205 km/h.

The DC motor has the advantage of being easy to grasp, as the two coils that make it up are not only fixed in space thanks to the action of the commutator, but also loosely coupled. It therefore offers an easy introduction to the operation of its counterparts, providing clear reference points that the neophyte can always hold on to.

For a long time, DC motors were the only motors suitable for high-bandwidth variable speed (robotics). As a result, they have undergone numerous improvements, and many of the products marketed today have nothing to envy their brushless counterparts.

Advances in power electronics have dethroned brushless machines in favor of self-driving synchronous technologies. But the essential reasons for these choices remain access to higher speeds, greater compactness and, very rarely, reliability.