PC/CP300 Electronics Laboratory II

Output Transducers: DC Motor

Equipment

• DC motor
• plastic wheels for load
• variable power supply

Procedure

1. What is the motor's resistance?
   
   
2. For the following questions, test the motor without the weight of the robot (e.g. upside down).
   • What current is required to start the motor?
   • What voltage is required to start the motor?
     
     
   • Did the ratio of voltage to current match the resistance you measured? Is this what you expected?
   • Observe the ac component of the voltage across the motor on an oscilloscope. What do you notice?
   • Disconnect the motor from the voltage supply and observe the ac component of the voltage across the supply on the scope. Does it look different from when the motor was connected? If so, how?
   • Reconnect the motor, but now put a reverse-biased diode across the motor and observe the ac component of the voltage. How does it compare to the previous two situations?
     From now on, always use a diode across the motor coils.
3. Normally, the current/voltage required to start the motor is different from the current/voltage required to keep the motor going.
   Decrease the current until the motor stops.
   • What current is required to keep the motor going?
   • What voltage is required to keep the motor going?
     
     
   • Did the ratio of voltage to current match the resistance you measured? Is this what you expected?
4. Change the equipment setup by turning the robot right side up and adding a battery (for weight). You'll probably need to use long leads for when the robot moves.
   
   
5. For the second equipment configuration, start the motor from an " at rest " position.
   • What current is required to consistently start the motor?
   • What voltage is required to keep the motor moving?
     
     
   • Did the ratio of voltage to current match the resistance you measured? Is this what you expected?
6. For the second equipment configuration, decrease the current until the motor stops.
   • What current is required to keep the motor moving?
   • What voltage is required to keep the motor moving?
     
     
   • Did the ratio of voltage to current match the resistance you measured? Is this what you expected?
7. Does the current/voltage required to start the motor depend on load? If so, give details.
   
   
8. Does the current/voltage required to keep the motor going depend on load? If so, give details.
   
   
   Demonstrate the DC motor in operation, showing effects due to load.