p.8 Brushes in the motor would touch the commutator, and send electricity into the coil. The commutator’s division position will determine the changing time of the electromegnetic polar, so that the motor can keep rotating.
p.11 A real DC motor has 3 commutator to avoid short-circuit, or it stop moving. GIF example here.
p.12 The reason for the cause of the spark, is the same with the “backflow voltage”(usually avoid by a flyback diode) of the motor. When the current is cut very suddenly, the magnetic field exists would actually generate a current for a short amount of time. So for the spark, it’s the air ionized because of the high electricity potential difference generated between the brush and commutator. (spark only exist when there is air gap)
flyback diode
p.20 The max Amp capacity of a flyback diode should be able to handle the current that the motor is going to use when it’s running normally, this is because when the circuit is opened, the magnetic field would actually want to generate a current the same amount as the circuit is closed. Reverse current in a diode: meaning the max amount of current that can actually leak through in the “wrong direction” (Nothing is perfect!)
Brake mode of motor H-bridge:
Commercial H-bridge normally has flyback diode and brake mode
Brush material: usually soft and conductive (carbon), so it wouldn’t wear off the commutator
