I read in an online book at https://www.learncse.com/images/Lessons/Lesson_14.pdf following reason for using a voltage regulator to power DC motors. While I understand the importance of using a regulator in certain situations, I am not convinced of the reason given. Please let me know if the following is correct?
The lesson as posted at https://www.learncse.com/images/Lessons/Lesson_14.pdf is to control a DC motor using an H-bridge and interfaced with an Arduino.
One characteristic of the DC motor that is very important for the purposes of this lesson is the motor's electrical resistance. The slower the motor turns the lower its electrical resistance and, therefore, the greater its demand for electrical current.
The reason this is important is that in these lessons the motors are powered by batteries. Batteries, in turn, have an internal resistance. As the resistance of a motor goes down, the voltage across the motor also drops as the proportion of the battery's internal resistance to total resistance increases. The result is all motors being driven by the batteries slow. To the observer, the DC motors just seem to be running rather poorly.
To minimize that effect, this lesson uses a battery with a higher voltage than what was intended for the motor and a voltage regulator to maintain the voltage delivered to the motor at a lower but constant value. This approach works because the internal resistance of the battery impacts the voltage being delivered to the regulator, not to the motor.