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 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.

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

 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.

 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.

 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).