While the motor is spinning, I measured the voltage (Vrm) across the motor by connecting the two probes from the multimeter to the two terminals of the DC motor via alligator to alligator banana cables. Since the current was fairly constant, I could ignore the inductance. So, no voltage across the inductor. As I connected the DC source directly to the motor, the duty cycle is 100%. Voltage effectively applied to the motor is 9V (the source input voltage). Voltage drop over motor resistance is the Vrm. Back EMF is then 9V-Vrm. Is this a valid way to measure the Back EMF?