Luckily, you can use any unipolar motor as a more efficient bipolar motor with a simple xacto knife modification. The extra wires in a unipolar motor are taps for each of the coils. Simply ...

Ergo, caveat emptor. The difference between unipolar and bipolar design is covered in this stepper motor overview by Monolithic Power. A unipolar stepper motor like the 28BYJ-48 has four phases ...