I work as an engineer and I've been looking for an explanation for something that I have been puzzled by. Physics background of problem: In brushed DC motors, electrical coils (poles) rotate as the motor moves. A change in inductance as they move makes small variations in motor current arise. It would be intuitive for these ripples to decrease in magnitude over the lifetime of a motor but this doesn't seem to be the case based on data from a motor manufacturer and ripple images found in "Brush wear detection by continuous wavelet transform." (The paper however does not focus on magnitude so it can't be conclusive evidence for this) I would expect the magnets in the motor to lose their magnetism as the motor heats and cools during its life cycle. This change should be small with modern magnets but it should still decrease the back emf constant of the motor and decrease the ripple magnitude. How could motor ripple actually increase over the lifetime of a motor?