DC ELECTRICAL MOTORS

  INTRODUCTION TO DC ELECTRICAL 
  MOTORS:




   

1.Motors Everywhere!

The fan over the stove and in the 

microwave oven

—
The dispose-all under the sink

—The blender

—

The can opener

—The washer 

—

The electric screwdriver  

—

The vacuum cleaner and
the Dustbuster mini-vac

The electric toothbrush

The hair dryer 

2.Important Concepts

How Motors Work.

The Components of a DC Electric
Motor 
What’s inside the motor box?
The parts of the motor and what they do!
Motor Control.
How to change directions.
—Concepts of Speed, Torque, Gear Ratio.

—

Practical considerations.

Noise, slippage, limits of operation

speed, torque.

—

3.DC Electric Motors:

—


Electric Motors or Motors convert 

electrical energy to 

mechanical motion

—
Motors are powered by a source of 

electricity – either AC 

or DC.

—

—DC Electric Motors use Direct Current 

(DC)sources of electricity:

Batteries

—DC Power supply

—

4.Principle of How Motors Work: 

—


Electrical current flowing in a loop of 

wire 

will produce a 

magnetic field across the loop.              

    
When this loop is surrounded by the 

field 

of another 

magnet, the loop will turn, producing 

a 

force (called

torque) that results in mechanical 

motion.

5.—Motor Basics

—

Motors are powered by electricity, 

but rely on principles of magnetism to 

produce mechanical motion.

—Inside a motor we find:

—Permanent magnets,

—

Electro-magnets,

—Or a combination of the two. 

6.—Magnets:

—

A magnet is an object that possesses a 

magnetic field, characterized by a 

North and South pole pair.

—

A permanent magnet (such as this bar 

magnet) stays magnetized for a long 

time. 

—

— An electromagnet is a magnet that is 

created when electricity flows through a 

coil of wire.  It requires a power source 

(such as a battery) to set up a 

magnetic 

field.

7.—A Simple Electromagnet:

A Nail with a Coil of Wire

Q – How do we set up a magnet?

—A – The battery feeds current 

through the coil of wire.  Current 

in the coil of wire produces a 

magnetic field (as long as the 

battery is connected).

8.—The Electromagnet 

in a Stationary Magnetic 

Field:

• 

—If we surround the electromagnet 

with a stationary magnetic field, 

the poles of the electromagnet 

will attempt to line up with the 

poles of the stationary magnet.

—

——The rotating motion is 

transmitted 

to the shaft, providing useful 

mechanical work.  This is how 

DC motors work!

—

9.Motor Terminology:

—

Thus, the motion of a DC motor is 

caused by the interaction of two 

magnetic fields housed inside 

the motor.

—These two magnetic fields can 

be described by where they are 

located inside the motor.

—

—The stationary parts of the 

motor make up the STATOR.

The Stator Stays Put!

—

The rotating parts of the motor 

constitute the ROTOR.

—The Rotor Rotates!

—The Stator houses the 

Permanent Field Magnet.

—The electronically-controlled 

magnet, called the Armature, 

resides on the Rotor. 

10.—Brushed DC 

Motor ComponenDescriptions:

—

The Stator is a Permanent Field 

Magnet

—

The Armature

—Is an electromagnet comprised of coils wound around 2 or more poles of the metal rotor core 

—

Commutator

—Attached to the rotor and turns with the rotor to mechanically switch direction of current going to the armature coils

—

Brushes

—Stationary attached to battery leads.  These metal brushes  touch the Commutator terminals as it rotates delivering electric current to the commutator terminals.

—Axle or Shaft

Moves in rotational motion.

11.—Controlling Motor Direction:

—In the TekBot, this switching

 isdone using an “H-bridge” 

motor control circuit.

—A signal is sent from your 

hand-

held tether to the TekBot 

when you tell each wheel to

go forward or reverse.

—This signal goes to the H-

bridgecircuitry on the 

TekBot which sends the

correct polarity to 

the battery leads wired to the 

TekBot motors to accomplish 

the desired rotation.

—12.Torque Concepts:

—

The movement of the motor comes 

from the interaction of magnetic 

fields. 

—A magnetic force that is 

perpendicular 

to the magnetic field and the 

current 

in the coils delivers a rotational 

force - 

torque - that turns the axle of the 

motor.

—

Intuitively, the higher the torque 

the 

greater the force of rotational 

movement.

—

The higher the motor input 

current, 

the greater the torque on the 

output.

13.—Speed Concepts:

—Speed of rotation of the output 

shaft is measured in RPM – “

Revolutions Per Minute”.

—The speed of rotation is directly 

proportional to the voltage 

applied to the armature 

windings.

This is a linear relationship up to 

the motor’s max speed.

—

These motors produce high 

speed, low torque axle rotation, 

which is improved by a gear 

reduction to reduce speed and 

increase torque on the output 

shaft. 

—14.TekBot Motor Ratings:

—

“GM8 - Gear Motor 8 - 143:1 Offset 

Shaft”

—

143:1 gear motor (“gear ratio”)

—spins at 70RPM at 5V, (maximum 

speed)

—

drawing 670mA at stall (“stall 

current”)

—generating 43 in*oz torque (free 

running at 57.6mA).

15.—Characteristics of Brushed DC Motors:

—Very commonly used in everything from 

toys to toothbrushes, electric toys to 

mobile robots.

—

Easy to control using simple control 

circuitry

—Small, Cheap

—Generally not used in industrial 

applications.

16.—DC Motor Varieties:

—

Brush-type DC Motor

—

Used for RPM under 5,000

—

Simpliest to control

—

Very common choice for hobby use

—Brushless DC Motor 

(a.k.a  AC Synchronous Motor)=

—Better suited for applications that 

require alarge range & precise speed

—Extra electronics for control and 

position 

sensors are required

— 

Wound-field DC Motor =

—

Common in industrial applications

—

Allows for wide range of precision speed control 

&  torque control 

—

Permanent Magnet DC Motor =

—

The field magnet is a permanent 

magnet and 

does not need to be activated by a 

current

—Intermittent vs. Continuous Duty =

—Continuous Duty motors can operate without an off period.

—Electric motor power rating =

—hp = (torque X rpm)/5,250