1. Stepper Motor
A stepper motor or step motor or stepping motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can then be commanded to move and hold at one of these steps without any feedback sensor (an open-loop controller), as long as the motor is carefully sized to the application in respect to torque and speed.
Stepper motors are DC motors that move in discrete steps. They have multiple coils that are organized in groups called "phases". By energizing each phase in sequence, the motor will rotate, one step at a time. With a computer controlled stepping you can achieve very precise positioning and/or speed control. For this reason, stepper motors are the motor of choice for many precision motion control applications.

2. Stepper Motor / Electro magnet

3. Rotor
Stator
Outside Casing
Stator
Rotor
Internal components of a Stepper Motor
Coils

4. Cross Section of a Stepper Motor
Stators
Rotor

5. Half Step Operation
Eight steps per. revolution i.e. 45 deg. steps.

6. Full Stepper Motor Half Stepper Motor
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
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.

7. Full Stepping
Animation shows how coils are energized for full steps

8. Stepping Sequence Half step sequence of binary control numbers
Full step sequence showing how binary numbers can control the motor
Half step sequence of binary control numbers

9. Stepper motor applications
Paper feeder on printers
Stepper motors
CNC lathes

10. Advantages / Disadvantages
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