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174 Making Things Move

Unipolar Stepper Motors
Unipolar, or four-phase, steppers have five, six, or sometimes (but rarely) eight wires.
They have four sets of wire coils alternating around the outside of the motor housing
(hence the term four-phase). Unipolar steppers energize the coils all at the same
polarity, or direction of current flow (hence
FIGURE 6-34 Schematic of a six-wire
the term unipolar).
unipolar stepper motor
A five-wire stepper is the same as a six-wire
stepper with the center connections (wires 5
and 6 in Figure 6-34) joined. The six-wire
configuration shown in Figure 6-34 is the
most popular and probably what you’ll find
when you pull a stepper motor out of a
printer. If you come across an eight-wire, or
universal stepper motor, it actually has four
independent coils with two connections to
each. These can be wired as a unipolar or
bipolar stepper.

NOTE A six-wire unipolar stepper is just like a bipolar stepper motor but
with center connections on each coil. It can also function as a bipolar stepper
motor if the manufacturer has designed it that way.

There are many options for controlling your stepper motor. To minimize time spent
with breadboards and programming, it’s best to consider ready-made modules that
can handle all the hard work of feeding current to the correct wires the right way.
Here are some suggestions:

• SparkFun’s EasyDriver (ROB-09402) will work with unipolar stepper motors
with six or eight wires that are wired as bipolar steppers. This module will
work with anything that can generate a 0 to 5V pulse (your Arduino comes in
handy here).
• You can use the Arduino to drive the motor directly, but there is more
programming involved and you need some extra chips and a breadboard.
Luckily, this is mostly done for you. Check out the Arduino stepper tutorial and
library at www.arduino.cc/en/Tutorial/Stepper. The code works the same for
unipolar and bipolar stepper motors.