Stepper Motors

Intro

Stepper motors are constant power motors. Unlike DC motors which rotate by create a reversing magnetic field stepper motors work by attracting a rotor core with magnetic coils aligned in a stator using discrete intervals called steps.

Advantages

Open loop, meaning there is no secondary sensor monitoring the position. In some cases this makes it cheaper to implement a digital controller.
The errors associated with steppers are non cumulative so even running it in open loop will usually yield accurate positions.
Full Torque Standing Still
reliable, contactless

Disadvantages

low torque
high vibration
limited speed
Resolution is limited to a multiple of it's step intervals.
Continuous Power Device

Bipolar vs Unipolar

Unipolar - motors are usually 5 or more conductors, all unipolars can be wired as bipolar

Bipolar (series) - usually 4 conductors, require a h bridge driver

Bipolar (Parallel)

Bipolar (series)

Probotixs Explaination

Drivers

Constant Voltage (L/R)

Constant Current (Chopper)

Bipolar Stepper Driver Example

Stepping Schemes

Wave Stepping - (1 Phase on) This is the most power efficient method for stepper but supplies the least torque. this also makes it the least stable at higher speeds

Phase	A	B	C	D
State1	1	0	0	0
State2	0	1	0	0
State3	0	0	1	0
State4	0	0	0	1

Full Stepping - (2 Phases on) offers half the resolution of wave stepping, but has a higher holding torque

Phase	A	B	C	D
State1	1	1	0	0
State2	0	1	1	0
State3	0	0	1	1
State4	1	0	0	1

Half Stepping - (1 or 2 Phases on) a hybrid of wave and full stepping this offers higher resolution torque and speed.

Phase	A	B	C	D
State1	1	0	0	0
State2	1	1	0	0
State3	0	1	0	0
State4	0	1	1	0
State5	0	0	1	0
State6	0	0	1	1
State7	0	0	0	1
State8	1	0	0	1

Micro Stepping - (continually varying currents)

Wiring

4 wire - Bipolar

8 wire - Unipolar or Bipolar

Steps per revolution

Common Step angle 1.8 deg (200 steps per rev)

NEMA Sizes

NEMA is a standard of stepper motor sizes. A 17 means the faceplate is 1.7inch wide. This also means that a motor that is a NEMA17 will fit onto the faceplate of any other NEMA17 motor. However the internals and the length of the stepper may vary and are usually defined by a longer more detailed suffix in the name.

NEMA 17 (<180 Oz. In torque)

NEMA 23 (180-400 Oz. In torque)

NEMA 35 (400-1200 Oz. In torque)

Reprap explaination of NEMA nameing convention