I used the Sanyo Denki Stepper Motor for my final year project. I really didn't know why it often got mad that it vibrated on its own and didn't rotate at all. Bad smell will then be occurred. But sometimes it worked properly and ran very smooth. Actually, I didn't think the problems came from my micro-controller board (8052 + 8255) as everything is alright except the motor part. In addition, when the motor got mad, I needed to turn off the power and gave it a little bit rotation and then ran the computer program again. It worked fine again. Can anyone tell me why?