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2-2 Phase 12-Volt 90 Ohm Unipolar Stepper Motor (#27964) Parallax, Inc. Stepper Motor (#27964)

Version 1.2 Page 1



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Rocklin, California 95765, USA
Office: (916) 624-8333
Fax: (916) 624-8003

General: info@parallaxi.com
Technical: support@parallax.com
Web Site: www.parallax.com
Educational:
http://www.parallax.com/html_pages/edu/index.asp


2-2 Phase 12-Volt 90 Ohm Unipolar Stepper Motor (#27964)

General Information


Stepper motors are ideally suited for precision control. This motor
can be operated in forward/reverse with controllable speed from a
BASIC Stamp or any other microcontroller through a transistor driver
circuit. Some of the applications for this motor include educational
experimentation, robotics and precision mechanical control

The #27964 is a Unipolar (2-2 phase) 12 VDC, 500 mA motor that
takes 3.75 degrees per step.



Note: photo may not match unit.

Technical Specifications


Number of Steps per Rotation 96(3.75deg/Step)

Drive Method 2-2 PHASE Drive Circuit.

Drive Voltage 12[V]

Coil Resistance/Phase 90ohm

Drive IC SMDT-002

Magnet Material Nd-Fe-B bonded magnet

Insulation Resistance 100Mohm MIN

Dielectric Strength AC 500[V] 1[min]

Class of Insulation CLASS E

Operating Temp. -10[C] ~ 50[C]

Storage Temp. -30[C] ~ 80[C]

Operating Hum. 20[%] RH ~ 90[%] RH


Dimensions

Motor Control from a BASIC Stamp


Parallax (www.parallaxinc.com) publishes many circuits and examples to control stepper motors. Most of
these examples are available for download from our web site. On www.parallaxinc.com type in stepper
motor and youll find example codes below.



Parallax, Inc. Stepper Motor (#27964)

Version 1.2 Page 2


The Parallax examples we drive the motor through a ULN 2803 high-current transistor driver as shown
above. Unlike ordinary DC motors, which spin freely when power is applied, steppers require that their
power source be continuously pulsed in specific patterns. These patterns, or step sequences, determine
the speed and direction of a steppers motion.

The fixed stepping angle gives steppers their precision. As long as the motors maximum limits of speed
or torque are not exceeded, the controlling program knows a steppers precise position at any given time.

Steppers are driven by the interaction (attraction and repulsion) of magnetic fields. The driving magnetic
field rotates as strategically placed coils are switched on and off. This pushes and pulls at permanent
magnets arranged around the edge of a rotor that drives the output shaft. When the on-off pattern of the
magnetic fields is in the proper sequence, the stepper turns (when its not, the stepper sits and quivers).

The normal stepping sequence for four-coil unipolar steppers is shown below.




Step Sequence


1
2
3
4
1
I/O pin 4 controls this coil Coil 1 (B)
1
1
0 0 1
I/O pin 5 controls this coil Coil 2 (B-)
0
0
1
1
0
I/O pin 6 controls this coil Coil 3 (A)
1
0 0
1
1
I/O pin 7 controls this coil Coil 4 (A-)
0
1
1
0 0









+12 VDC
P4
P7
P6
P5
12 VDC Unipolar
Stepper Motor
9
GND
Red
White
Orange
Blue
10 Brown
ULN2803
2
3
4
16
17


From a microcontrollers standpoint, causing the motor to take a step involves taking two pins high at
a time through the driver circuit shown above.

Stamp1

pins =%11110000
symbol loop = b0
symbol delay = b1

pins = %11110000

delay = 400 'slow the step speed

start:
for loop = 1 to 10 'do this 'loop' times
pins = %01010000 'I/O pins 0 and 2 high
pause delay
pins = %10010000 'I/O pins 0 and 3 high
pause delay
pins = %10100000 'I/O pins 1 and 3 high
pause delay
pins = %01100000 'I/O pins 1 and 2 high
pause delay
pause 2500
next

Parallax, Inc. Stepper Motor (#27964)

Version 1.2 Page 3


Stamp 2 ,2e,2sx,2p

loop var nib
delay var byte
dirb = %1111

delay = 400 'slow the step speed

start
for loop = 1 to 10 'do this 'loop' 10 times
outb = %0101 'I/O pins 0 and 2 high
pause delay
outb = %1001 'I/O pins 0 and 3 high
pause delay
outb = %1010 'I/O pins 1 and 3 high
pause delay
outb = %0110 'I/O pins 1 and 2 high
pause delay
pause 2500
next
stop