A single, 180-degree turn is all you would get out of this motor if it weren't for the commutator. The commutator is a metal ring that has been split, leaving an important gap between halves (represented here in red and blue.) Each half of the commutator is connected to an end of the rotor. Current is delivered to one half of the commutator via the brush. When the brush reaches the gap between halves, the current changes direction. The change in direction reverses the magnetic field (indicated by green arrows here) of the rotor, causing it to spin again to realign with the field of the permanent magnet. This process repeats and the rotor keeps spinning, creating a motor.