Brushed motors, the oldest DC motor technology, are the simplest and lowest cost option (Figure 2). Due to the contact between the current-carrying brush and the rotor, the rotation of the motor rotor switches (steers) the field around the windings around the rotor. The speed of the motor is a function of the applied voltage, so the drive requirements are not high, but managing torque and associated positions is difficult. The driving conditions also have reliability problems due to wear of the motor, cleaning required due to dirty brushes and springs, and sparks generated by brush and rotor contact, which may become sources of electronic noise (electromagnetic interference). Due to these problems, in most cases, brushed motors are the least attractive option for robot design.
Figure 2: In a brushed motor, a conductive brush (made of copper bristles or more likely to be made of graphite) contacts the contacts on the rotor. As the rotor changes direction, it switches the polarity of the surrounding coil current
