A stepper motor has a magnetic field which is on a armature which is like a long cog, so it has lots of bars running down it, each bar is a north pole or a south pole. The windings are sets of fixed coils again with lots of " teeth" pointing inwards. The armature aligns the teeth, then when the coils are pulsed, the field moves one tooth around , so the armature, "steps" one tooth around to follow it. The effect is that the position of the rotor can be accurately controlled by altering the number of pulses applied. Typically, there will be 100 -> 200 steps per revolution. So to make it spin like a typical motor you need to have a pulse generator continuously supplying pulses to the coils in the right order.
In your application, I would think that a bridge rectifier across each set of windings and connect the DC outputs to gather is the best you can do.
Frank