2, there is a same motor that turn 90 ̊, however, the polarity do not change in this figure, because the brushes are touching the same commutator plates as shown in Fig. 1.
In Fig. 3, it shows that the armature is in a horizontal position and armature A and B do not have any polarity. This is because both of the brushes are not touching the commutator plate 1 or 2. Therefore, in that position the current flow cannot pass though the armature, so there is no polarity in armature A or B. This also is the position that prepare for the armature A and B change polarity.
Fig. 4 is in this position, because the magnet will repulse at the first second of the current flow in the opposite direction. Fig. 4 also has a similar picture with Fig. 1; however, look closely one will find out that the armature A and B switch polarity. This is because the commutator plate 1 and plate 2 is not touching the same brushes as Fig. 1 show. When the brushes are not touching the same commutator plate as Fig. 1 show the current flow changes in opposite direction. Therefore, the polarity of armature A and B change. This also allows the motor to