In electrical engineering, an armature is one of the two principal components of an electro-mechanical machine--a motor or generator. The other is the field winding or field magnets. In an electric motor used in radio control, the armature is the rotating part within the motor's outer can. It is the rotating armature which creates the mechanical energy necessary to propel a model or move a servo. The role of the "field" component is simply to create a magnetic field (magnetic flux) for the armature to interact with, so this component can comprise either permanent magnets, or electromagnets formed by a conducting coil. The armature, in contrast, must carry electrical current or electromotive force or EMF (usually both), so it is always a conductor or a conductive coil, oriented normal to both the field and to the direction of motion, torque (rotating machine), or force (linear machine). The armature's role is two-fold: (a) to carry current crossing the field, thus creating shaft torque (in a rotating machine) or force (in a linear machine), and (b) to generate an electromotive force. In the armature, an electromotive force is created by the relative motion of the armature and the field. When the machine is acting as a motor, this EMF opposes the armature current and the armature converts electrical power to mechanical torque (and power, unless the machine is stalled) and transfers it to the load via the shaft. When the machine is acting as a generator, the armature EMF drives the armature current, and shaft mechanical power is converted to electrical power and transferred to the load. (In an induction generator, these distinctions are blurred, since the generated power is drawn from the stator, which would normally be considered the field.)
In alternating current machines, the armature is usually stationary (the "stator"). In DC rotating machines other than "brushless DC" machines, it is usually rotating (the "rotor").
The pole piece of a permanent magnet or electromagnet and the moving, iron part of a solenoid, especially if the latter acts as a switch, may also be referred to as armatures.