[Bassnut (Fred)]

This a bit of a long shot, but someone may know off hand.

Ive nearly finished a timelapse controller that has been designed around PICAXE (PIC CPU) and bipolar stepper motors using a standard L297/L298 chip set for driving. The L298 has 4 H bridge outputs for each side of 2 bipolar motor windings, works a treat. They are 6v driven from 12v but current limited per step..

I need to now drive 12v unipolar steppers, 4 windings with a common B+ to all 4 at the other end. Easy I thought, the step sequence is the same, just connect the same 4 outputs to the 4 coils, and common the other ends to 12v.

It works, but only slowly and no guts.

Typical unipolar driver outputs are single ended not H bridge, but I wouldve thought that wouldnt make a difference, the top H bridge tranny just shorts to + 12v instead of O/C (maybe thats the prob?).

Is there some big difference driving unipolar over bipolar?, I cant see anything on the interweb that tells me anything on the diff.

Im not looking for advice on a total redesign, just a clue on the diff.

Im wondering if a 12v stepper windings driven from single ended 12v driver is way less powerfull than H bridge 6v motors current limited?, given H bridge effectively swings bipolar windings 24v.