These motors come in a variety of flavors, from the four-wire deals you find in 3D printer builds, to motors with five or six wires. Unipolar motors – the ones with more than four wires – are easier to control, but are severely limited in generating torque. Luckily, you can use any unipolar motor as a more efficient bipolar motor with a simple xacto knife modification. - hackaday.com

see also

• Introduction to Stepper Motors for 3D Printing - The Basics you probably need to know - Episode 1

28BYJ-48 Stepper / ZC-A0591 ULN2003 Driver

• openscad model

AccelStepper

Tutorials

• 28BYJ-48 Stepper Motor with ULN2003 Driver
• BYJ48 Stepper Motor
  • 28BYJ-48
  • ULN2003

Thingiverse

• Linear mechanism
• direct drive