I have come across one of these stepper motors Item # PK243-01AA, Stepper Motor On Oriental Motor USA, but I'm not sure if it's the unipolar or bipolar model. There are no markings on the motor to indicate bipolar or unipolar. It has six leads, so based on my reading, I believe it is unipolar? How can I tell which one it is?
Based on the spec page, it looks like it runs off of 4 volts at 0.95 amps. This is drawing too much from the Arduino, correct? I'll have to supply power externally, right?
6-wires can be used as unipolar or bipolar. If you want to be sure measure the winding resistances and compare with the options available. 0.95A is too high (especially as you activate two windings at a time in full-stepping mode). So a separate 5V 2A supply would prob. be needed (you lose about 1V in a darlington driver). You either need to parallel up some ULN2004's to deal with the higher current/power dissipation or use separate power darlingtons.
If it is 4V then a 4V supply would be best if using MOSFET drivers since they don't have 1V saturation.
With separate driver transistors remember you require freewheeling diodes.
Or you can get a bipolar driver board such as the dinky little Polulo one with the A4988