CRE Power Systems & Actuators

Question 1

Which type of actuator converts electrical energy into rotational motion using the interaction of magnetic fields and current-carrying conductors?

Accepted Answer

DC electric motor

Answer

A DC electric motor converts electrical energy into rotational mechanical motion through electromagnetic force between the stator's magnetic field and the rotor's current-carrying windings.

Question 2

In a brushless DC (BLDC) motor, what component performs the commutation function that brushes handled in a brushed DC motor?

Accepted Answer

Hall effect sensors and electronic speed controller (ESC)

Answer

In a BLDC motor, Hall effect sensors detect rotor position and feed data to an ESC, which electronically switches current to the appropriate stator windings for commutation.

Question 3

A robotic joint requires 50 N·m of torque and the selected motor produces 5 N·m. What gear ratio is needed to meet the torque requirement (ignoring efficiency losses)?

Accepted Answer

10:1

Answer

Gear ratio = required torque / motor torque = 50 N·m / 5 N·m = 10:1, meaning the gearbox multiplies torque tenfold while reducing output speed proportionally.

Question 4

Which actuator type is most suitable for high-force, precise linear motion in a clean-room robotic assembly environment where leaks are unacceptable?

Accepted Answer

Electric linear actuator

Answer

Electric linear actuators are ideal for clean-room environments because they produce no fluid leaks, offer precise position control, and require no compressors or hydraulic power units.

Question 5

What is back-EMF (back electromotive force) in a DC motor, and what effect does it have on motor current?

Accepted Answer

A voltage generated by the spinning rotor that opposes the supply voltage, reducing current draw

Answer

Back-EMF is generated by the rotating rotor acting as a generator; it opposes the supply voltage and reduces current draw, limiting speed and providing a natural speed-regulation mechanism.

CRE - Certified Robotics Engineer Practice Test

CRE - Certified Robotics Engineer Practice Test

CRE Power Systems & Actuators