CRE Power Systems & Actuators 2 — Questions and Answers
Question 1: A stepper motor is specified as 1.8° per step. How many steps are required to complete one full 360° revolution?
- 100 steps
- 180 steps
- 200 steps (Correct answer)
- 400 steps
Correct answer: 200 steps
360° ÷ 1.8°/step = 200 steps per revolution; this is the standard step count for a 1.8° stepper motor in full-step mode.
Question 2: What is the primary advantage of using PWM (Pulse Width Modulation) to control a DC motor's speed compared to varying supply voltage directly?
- PWM eliminates the need for a motor controller
- PWM allows precise speed control with high efficiency by rapidly switching full voltage on and off (Correct answer)
- PWM reduces motor inductance and eliminates back-EMF
- PWM enables the motor to run in reverse without an H-bridge
Correct answer: PWM allows precise speed control with high efficiency by rapidly switching full voltage on and off
PWM controls average power delivery by rapidly switching full supply voltage on and off at varying duty cycles, maintaining high efficiency because the switching transistor dissipates minimal power compared to linear voltage reduction.
Question 3: In a robotic power system, what is the purpose of an H-bridge circuit?
- Step up DC voltage for high-torque motor applications
- Allow bidirectional control of a DC motor using four switching transistors (Correct answer)
- Filter EMI noise from motor windings back to the power supply
- Provide regenerative braking energy storage
Correct answer: Allow bidirectional control of a DC motor using four switching transistors
An H-bridge uses four transistors arranged in an 'H' pattern; by selecting which pair conducts, current direction through the motor can be reversed, enabling forward and reverse rotation control.
Question 4: Which type of hydraulic pump is most commonly used in industrial robot power units due to its consistent flow rate and ability to maintain pressure against varying loads?
- Centrifugal pump
- Gear pump
- Axial piston pump (Correct answer)
- Peristaltic pump
Correct answer: Axial piston pump
Axial piston pumps are preferred in industrial hydraulic robot systems for their high efficiency, variable displacement capability, and ability to maintain consistent high pressure against varying actuator loads.
Question 5: What is the function of a flyback diode (freewheeling diode) placed across a DC motor's terminals in a motor drive circuit?
- Prevent current from flowing backward through the motor
- Protect the motor driver from voltage spikes caused by the motor's inductive kickback when power is cut (Correct answer)
- Regulate the motor's supply voltage to a safe operating level
- Increase motor efficiency by recovering regenerative energy
Correct answer: Protect the motor driver from voltage spikes caused by the motor's inductive kickback when power is cut
When motor power is switched off, the motor's inductance causes a voltage spike (kickback); the flyback diode provides a safe current path to dissipate this energy and protect the switching transistors.
Question 6: In a battery-powered mobile robot, what does 'C-rating' indicate on a LiPo battery specification?
- Cell chemistry type (C for cobalt-based cathode)
- The battery's capacity in coulombs
- Maximum continuous discharge current as a multiple of the battery's capacity (Ah) (Correct answer)
- Charging cycle count before significant capacity degradation
Correct answer: Maximum continuous discharge current as a multiple of the battery's capacity (Ah)
C-rating defines the maximum safe continuous discharge rate as a multiple of the battery capacity; a 5Ah battery with 20C rating can deliver up to 100A continuously (5Ah × 20C = 100A).
Question 7: A servo motor system uses an encoder with 4,096 counts per revolution. What is the theoretical angular resolution in degrees per count?
- 0.044°
- 0.088° (Correct answer)
- 0.176°
- 0.352°
Correct answer: 0.088°
Angular resolution = 360° / 4,096 counts = 0.0879° per count ≈ 0.088°, meaning the system can distinguish position changes as small as 0.088°.
CRE Power Systems & Actuators 2
A stepper motor is specified as 1.8° per step.
How many steps are required to complete one full 360° revolution?