1. proto-pic.co.uk

2.  Simply speaking, a stepper-motor is a brushless
motor running on a DC current, which is able to
split one full rotation of a gear cog into a number
of equal steps. These steps do not have to be
sequential (i.e. in the same direction, rather than
moving first forward and then backward) – though
in the simplest configuration of the motor they
often are.

3. Stepper-motor with cable
This is a simple, but powerful stepper
motor with a 4-wire cable attached.

4.  The motor is activated using electromagnetic coils,
which magnetise cogs on the gear wheel. To move
the cog, the coil currently holding it is turned off
and a different one is turned on. The magnetic pull
the stepper-motor exerts on the cog teeth thus
causes the wheel to change position. One such
change is referred to as a “step”.
 The motor is used to make adjustments in
positioning devices, for example in the laser head
in a DVD or CD player. The clicking sound you
sometimes hear in older DVD and CD players is an
old stepper-motor losing its grip.

5.  The motor suffers from a lack of torque at higher
speeds. The faster the wheel turns, the more the
cog is likely to slip. So applications requiring the
motor to turn at high speeds may be better served
using a servo motor instead. The resonating effect
also exhibited by the stepper-motor at high speeds
may have an adverse effect on device performance.

6.  The plus points of the stepper-motor are many.
For example, its relatively low cost and high
reliability at low speeds make it ideal for a wide
range of amateur projects. While its simplicity of
design means it can operate in even quite difficult
conditions, where a more delicately calibrated
motor may have trouble functioning properly.
 The motor does suffer from limitations of size, in
that it gets too big where a large degree of steps
are required (and hence a large number of cog
teeth).