Mod 8 (DC Motors, Drives & Servos) - Homework

basic function of a DC motor

converts direct current (DC) electrical energy into mechanical energy.

role of brushes in a DC motor

transfer current from the stationary external circuit to the rotating armature windings.

Motor Action

when a current-carrying conductor is placed
within a magnetic field, it experiences a force perpendicular to both the direction of the
current and the magnetic field.

two main effects produced when a DC motor spins

torque and back electromotive force
(CEMF)

function of the yoke in a DC motor

provides mechanical support
for the internal components, such as the field poles, and protects them from external damage.
Additionally, it completes the magnetic circuit

main components of the rotor in a DC motor

• armature windings

• armature core

• the shaft

• commutator

armature windings

carry the current and generate the magnetic field

armature core

supports the
windings and concentrates the magnetic flux

the shaft

transmits the rotational motion
to the mechanical load

Series DC motor winding connection

connected in series with the armature winding, the same current flows through both

Shunt DC motor winding connection

connected in parallel (shunt) with the armature winding.

advantages of Permanent Magnet DC Motors (PMDC Motors)

• Simple

• Efficient

• Reliable

brushless DC motors

use electronic commutation, which involves sensors
and an electronic controller to switch the current

Why are series DC motors considered poor for speed regulation

their speed varies
significantly with changes in load

working principle of a servo motor

operates on the principle of feedback control, where the motor’s position,
speed, or acceleration is continuously monitored and compared to a desired setpoint.

key components of a servo motor system

• Motor

• controller

• feedback device

• Drive circuitry

torque ripple in PMDC motors

the periodic
fluctuations in torque as the armature windings interact with the fixed magnetic field of the
stator. These fluctuations can lead to vibrations and noise, reducing the smoothness of motor

Methods to control a DC Shunt motor

• vary the field current by adjusting the field resistance

• controlling the terminal voltage applied to the motor

primary advantage of cumulative compound motors

combine the characteristics of both series and shunt motors,
offering a balance of high starting torque and good speed regulation.

indexer in a stepper motor system

It converts the desired motion information, such as position, speed, or direction, into discrete move signals that are applied to the driver

Cumulative compound motors field windings

The magnetic fields of the series and
shunt windings aid each other

differential compound motor field windings

The magnetic fields oppose each other

significance of back EMF in DC Motors

• Regulates Speed

• Controls current

• Indicates energy conversion

mechanical braking

involves physical components like brake pads and drums to stop the
motor.

DC servo
motors are known for their

high efficiency and precise control

AC servo motors offer

higher power and robustness

components of a DC drive system

• Operator Control

• Drive Controler

• DC motor

• Speed regulator

Dynamic braking

disconnecting the motor from the power supply and connecting the
armature to a resistor, where the kinetic energy is dissipated as hea

Regenerative braking

recovers the kinetic energy by converting it back into
electrical energy, which is fed back into the power supply

What applications commonly use stepper motors

applications requiring precise control over
positioning, speed, and direction, such as 3D printers, medical devices, CNC machines, and
camera platforms