In Lap winding, the number of brushes is always double the number of poles.
In a lap winding, the armature conductors are connected end-to-end in a loop that passes through all the poles of the machine.
The winding is arranged in such a way that adjacent conductors in the loop are connected to opposite commutator segments.
For example, in a DC generator with four poles, there would be eight commutator segments, and therefore eight armature conductors in the lap winding.
The generator would require two brushes, with each brush making contact with four commutator segments (i.e., half of the total number of segments), to ensure that the current flows in the correct direction through the armature conductors.