1. Evaluating DC Motors Determining Motor Stall Current

2. Measuring Armature Coil Resistance The Multi-Meter selector is set to read resistance in units called ohms  (The Blue portion of the selection dial) The selector is set to the lowest range (0- 200  ) The Value measure is 0.9 ohms.

3. Measuring Armature Coil Resistance Set the meter to read ohms. Use the lowest range. Short the meter leads and record the value. This is the meter error value. Attach your meter to the two motor leads. Slowly turn the armature shaft and record values at 45° intervals. Average these values. Caution: Turning the armature shaft quickly, induces a current in the armature windings. This Will damage the meter.

4. Calculate the Stall Current I = E R Ohm’s Law The basic Algebra of electronics E = Voltage I = Current in Amperes R = Resistance in Ohms, 

5. Calculate the Motor Stall Current I = E R The sample motor yields an average measured resistance value of 0.6 . The intended BattleBot power supply will provide 12 Volts emf (electro motive force). The meter error = 0.3  40 amps = 12V 0.6  - 0.3  Predicted Motor Stall Current = 40 Amperes

6. Directly Measuring Motor Stall current is a Learning Experience. Ammeter Voltmeter Sample Motor NC MO Switch 12V Battery