DC Motors

• Only One Winding

• Two Connections: + and –
• Reversing Polarity -- Reverses Motor
• Move Continuously
• Cannot Determine Position
Characteristics:
• RPM
• No Load: Maximum RPM With No Load on Shaft
• Given in Data Sheets
• Loaded: Actual Maximum When Loaded
• Not in Most Data Sheets
• Voltage Range
• Speed Increases With Voltage on a Given Motor
• Current Draw
• Data Sheet Rating is With Nominal Voltage and No Load
• Increases With Load
• Speed Decreases With Load
DC Motor Rotation
(Permanent Magnet Field)
L293D DC Motor Driver IC
Input 1 = LOW(0v) Output 1 = LOW
Motor 1 rotates in Anti-Clock wise
Direction
Input 2 = HIGH(5v) Output 2 = HIGH

Input 3 = LOW(0v) Output 1 = LOW

Motor 2 rotates in Anti -Clock wise
Direction
Input 4 = HIGH(5v) Output 2 = HIGH

Input 1 = HIGH(5v) Output 1 = HIGH

Motor 1 rotates in Clock wise Direction
Input 2 = LOW(0v) Output 2 = LOW

Input 3 = HIGH(5v) Output 1 = HIGH

Motor 2 rotates in Clock wise Direction
Input 4 = LOW(0v) Output 2 = LOW

Input 1 = HIGH(5v) Output 1 = HIGH

Motor 1 stays still
Input 2 = HIGH(5v) Output 2 = HIGH

Input 3 = HIGH(5v) Output 1 = LOW

Motor 2 stays still
Input 4 = HIGH(5v) Output 2 = HIGH
Stepper motor
Stepper Motor
•A stepper motor is a special type of electric motor that moves in
increments, or steps, rather than turning smoothly as a conventional motor.
•
• Typical increments are 0.9 or 1.8 degrees, with 400 or 200 increments.
• The speed of the motor is determined by the time delay between each
incremental movement.
•
• Two types of stepper motor are:
1. Permanent Magnet (PM)
2. Variable Reluctance (VR)
Stepper Motor / Electro magnet
 Moving the Rotor

Unstable Stable

Rotor will ALWAYS seek a stable position.

 Rotor

Stator
Outside Casing

Coils Stator

Rotor

Internal components of a Stepper Motor

 Cross Section of a Stepper Motor

Stators

Rotor
Full Step Operation

Four Steps per revolution i.e. 90 deg. steps.

Half Step Operation

Eight steps per. revolution i.e. 45 deg. steps.

Single-Coil Excitation
Two-Coil Excitation
Interleaved Single- and Two-Coil Excitation

Half-Stepping
Single-Coil Excitation Two-Coil Excitation

Interleaved Single- and Two-Coil Excitation

Half-Stepping
Single-Coil Excitation - Each successive coil is energized in turn.
Two-Coil Excitation - Each successive pair of adjacent coils is
energized in turn.
Interleaving the two sequences will cause the motor to half-step
8 step sequence = normal 4 step + wave drive 4 step.
Winding number 1

One
6 pole rotor step

Winding number 2
Six pole rotor, two electro magnets.

How many steps are required for one complete revolution?

❑ Motor Moves Each Time a Pulse is Received.
❑ Can Control Movement (Direction and Amount) Easily.
❑ Can Force Motor to Hold Position Against an Opposing
Force.
How Far Does It Move?
• Step Angle
• Arc Through Which Motor Turns With ONE Step Change of the Windings.
• Varies With Model of Stepper Motor
(Depending on the number of teeth on stator and rotor).
• Normally in Degrees.
• Step angle = 360/No. of Steps per Revolution.
• Commonly available no. of steps per revolution are 500, 200, 180, 144, 72, 48, 24.
How Fast?

Revolutions per Minute (RPM)

 Practical Stepper motor operation

The top electromagnet (1) is turned on, attracting the nearest The top electromagnet (1) is turned off, and the right electromagnet
teeth of a gear-shaped iron rotor. With the teeth aligned to (2) is energized, pulling the nearest teeth slightly to the right. This
electromagnet 1, they will be slightly offset from results in a rotation of 3.6° in this example.
electromagnet 2
 The left electromagnet (4) is enabled, rotating again by 3.6°. When
the top electromagnet (1) is again enabled, the teeth in the sprocket
The bottom electromagnet (3) is energized; another 3.6°
will have rotated by one tooth position; since there are 25 teeth, it
rotation occurs.
will take 100 steps to make a full rotation in this example.
Drivers
• May Need a Driver Circuit
• Same Problem as Relays – May Draw Too Much Current
• Types
• Transistor Drivers
• Usually a Darlington Pair
• Darlington Arrays
• Can Build It Yourself
Using
Transistors
for Stepper
Motor Driver
Applications:
Used in
In instrumentation such as watches,
clocks, etc.
Computer peripherals such as card
readers, teleprinters, teletypes, dot matrix
printers, etc.
Robotics
 Stepper motor applications

Stepping Motor to move read-write head

 Stepper motor applications

Paper feeder on printers

Stepper motors

CNC lathes
 Stator coils

Rotor
CNC Stepping Motor
Advantages / Disadvantages
Advantages:-
•Low cost for control achieved
•Ruggedness
•Simplicity of construction
•Can operate in an open loop control system
•Low maintenance
•Less likely to stall or slip
•Will work in any environment

Disadvantages:-
•Require a dedicated control circuit
•Use more current than D.C. motors
•High torque output achieved at low speeds
Control sequence to turn a stepper motor
+

Step 1 0 0 1 1
CW CCW
Step 2 1 0 1 0
Step 3 1 1 0 0
Step 4 0 1 0 1
 Full Stepper Motor

• This animation demonstrates the principle for a stepper motor using full step commutation. The
rotor of a permanent magnet stepper motor consists of permanent magnets and the stator has two
pairs of windings. Just as the rotor aligns with one of the stator poles, the second phase is
energized. The two phases alternate on and off and also reverse polarity. There are four steps. One
phase lags the other phase by one step. This is equivalent to one forth of an electrical cycle or 90°.
 Half Stepper Motor

• This animation shows the stepping pattern for a half-step stepper motor. The commutation sequence for a
half-step stepper motor has eight steps instead of four. The main difference is that the second phase is
turned on before the first phase is turned off. Thus, sometimes both phases are energized at the same
time. During the half-steps the rotor is held in between the two full-step positions. A half-step motor has
twice the resolution of a full step motor. It is very popular for this reason.
 Stepper Motors

• Some stepper motor uses permanent magnets. Some stepper motors do not have magnets and instead
use the basic principles of a switched reluctance motor. The stator is similar but the rotor is
composed of a iron laminates.
 Full Stepping

• Animation shows how coils are energized for full steps

Half Stepping

• Note how the phases are driven so that the rotor takes half steps
 Stepping Sequence
• Full step sequence showing how binary
numbers can control the motor
 Stepping Sequence
• Half step sequence of binary control numbers
Stepper Motor Driver Board ULN2003
H-Bridge:
Enables you to control the motor in both
forward and reverse with a microcontroller.
• H-Bridge chips
• NSC LMD18200
• H-Bridge driver chips
• Intersil HIP4081A
 Servo Motor Detail Actuator

Reduction gear

Position feedback
Potentiometer
+ 5V (closed loop system)

Small electric DC motor