Measuring Inductance

The easiest way to measure inductance is to use a LCR meter. You can also use an oscilloscope with signal generator:

measuring inductance using an oscilloscope

Set up a potential divider circuit. Attach the N20 motor in place of R2. Use a signal generator to produce a sine wave on Vin. CH2 will measure the reference sine wave. When XL = R1 the amplitude of the signal in CH1 will be exactly half that of the measured reference signal. Adjust the frequency until this condition is met. Setting the V/div scale for CH 1 to half of that for CH2 makes this easier. The LCR meter measures 2.5 mH, the oscilloscope method gives 2.6 mH.