18 Part I: DC Motors – Understanding Motor Technologies – Review Questions

(PC: “Hand holding magnifying glass among a lot of questions. Finding answers to questions and solving problems” by wuestenigel is licensed under CC BY 2.0.)

Questions to review:

1. Multiple Choice: Brushed DC motors and permanent magnet DC motors are both common types of DC motors. What is the key difference in their component design that affects motor operation? a) Brushed DC motors use permanent magnets for stator field generation, while permanent magnet DC motors rely on electromagnets. b) Brushed DC motors have a higher torque output compared to permanent magnet DC motors. c) Permanent magnet DC motors are generally less efficient than brushed DC motors. d) Brushed DC motors require more complex control circuits compared to permanent magnet DC motors.

2. Short Answer: Explain the basic operating principle of a brushed DC motor. How does the commutation process ensure continuous rotation of the motor shaft?

3. Application Problem: An automated feeder system for a bottling plant requires a DC motor to precisely control the speed of a conveyor belt. Which DC motor control technique (permanent magnet motor reversing, SCR control, braking) would be most suitable for this application, and why?

4. Challenge Question: Imagine you are designing a robot that climbs walls. How could you potentially use DC motors with braking capabilities to improve the robot’s climbing performance?

5. True or False: Silicon Controlled Rectifiers (SCRs) can only be used to turn DC motors on and off.

6. Open Ended: Discuss the advantages and disadvantages of using brushed DC motors compared to brushless DC motors for a small, battery-powered robot.

7. Matching: Match the following DC motor control techniques with their corresponding functionalities:

    a) Permanent magnet motor reversing
    b) SCR control
    c) Braking
    d)  Speed control with Pulse Width Modulation (PWM)

    i) Allows for dynamic control of motor speed
    ii) Rapidly stops the motor shaft rotation
    iii) Changes the direction of motor rotation
    iv) Controls the motor power by regulating voltage

8. Design Challenge: You are tasked with designing a system to control the opening and closing of a motorized door. Describe the key components you would need and how DC motor control techniques would be implemented to achieve this function.

9. Think-Like-an-Engineer: Many automated systems utilize gearboxes in conjunction with DC motors. Explain the purpose of gearboxes and how they can affect the performance of a DC motor in an automation project.

10. Research and Report: Choose a specific application of DC motors mentioned in the module (e.g., electric vehicles, power tools) and research the additional control systems used to optimize motor performance in that application. Prepare a short report summarizing your findings.