When it comes to simple circuit analysis, there is millions of tutorials on how to analyze a resistor circuit, a RC circuit, or those involving LED the non-ohmic devices. However, I did not find a simple and clear tutorial on how DC motors behave within a circuit. I did some experiment, and only got more confused over the result. A brushless motor rated for 0.4A 5V when connected to a 9V it runs full speed without a problem, but then I add a little resistor to limit some current suddenly the motor hardly turns at all.
Summary of question: what is the behaviour of DC motors in a circuit? What does the rating 5V 0.4A mean? (the voltage drop? the forward voltage? etc.)