Concepts

Question 1

Sources of losses in electo mechanical devices

Answer 1

Losses in the electrical conductors
Losses in soft magnetic components (hysteresis and eddy losses)
Friction losses in mechanical system

Question 2

What is the purpose of a gearbox attached to a motor

Answer 2

Step up or step down speed

Question 3

Give a real life application of Lorentz magnetic force

Answer 3

Loudspeaker

Question 4

Which part of a loudspeaker moves

Answer 4

The electrical coil

Question 5

What assumptions would you make about the electric coil on a loud speaker

Answer 5

Uniformity- impedance, magnetic field

Displacement of the cone is proportional to applied force

Question 6

Basic elements of a rotary actuator

Answer 6

Simple 2 pole single phase stator winding.

Moving element - iron core with permanent magnet or a single dc field coil

Question 7

Uses of rotary actuators

Answer 7

Limited angle torque motors- scanning lasers and mirrors

Question 8

How to tell current direction on a diagram

Answer 8

Arrow
X going into page
. Coming out of page

Question 9

What equivalent represents back emf in a device

Answer 9

Capacitor

Question 10

How does voltage across a capacitor rise

Answer 10

Exponentially slower

Question 11

In a closed loop system how is the input to the servo amplifier calculated

Answer 11

Demand- Feedback= (error)

Question 12

Basic components of Dc commutator motor

Answer 12

Permanent magnets produce a vertical field. Two conductor on the central rotor

Question 13

At what point on a dc motor does the rotor have 0 torque

Answer 13

Perpendicular to the field

Question 14

What is done to prevent net torque of one rotation of a dc motor

Answer 14

Switching the polarity of the current (commutation)

Question 15

Advantages of DC motors

Answer 15

Very simple supply requirements
Straight forward control
Produce max torque at standstill
Low cost

Question 16

Disadvantages of DC motors

Answer 16

Friction from brushes
Sparking from commutator
Brushes have to be periodically replaced
Carbon deposits with machine
Copper loss occurs on rotor

Question 17

Increasing speed in a dc motor effect on armature current

Answer 17

Ia will reduce

Question 18

Relationship between T and w in a dc machine

Answer 18

Negative linear. \

Question 19

Tstall

Answer 19

Torque at 0 speed

Ability to Dissipate I^2*R loss in the armature

Question 20

In practice is torque required to maintain a speed

Answer 20

Due to frictional losses yes

Question 21

How does armature current/time compare to a torque/time graph (servo dc)

Answer 21

They look identical in theory but in practice it’s a slower rise with time constant L/R

Question 22

What is the steady state equivalent servo circuit

Answer 22

Va-Ra-Ia-back emf-