# Unipolar stepper motor and ½ steps

Here's someone testing a unipolar 5 wire stepper motor.

Am I on right track if I say this is whole steps? A 5 wire unipolar stepper motor needs 4 datapins and having each go high subsequently while the other three go low, will perform this action seen in the video, right? (Going high means opening a corresponding transistor, which will activate corresponding coil in the stepper motor.)

But most code for unipolar show a pattern of 8 steps, not 4:

``````     0   1   2   3   4   5   6   7
D0   HI  HI  LO  LO  LO  LO  LO  HI
D1   LO  HI  HI  HI  LO  LO  LO  LO
D2   LO  LO  LO  HI  HI  HI  LO  LO
D3   LO  LO  LO  LO  LO  HI  HI  HI
``````

So the even steps would be the whole steps, while the odd steps would be the added half steps. If I'm on right track, do all 5 wire stepper motors behave like this? Or are there motors uncapable of handling the half steps? Or are there motors requiring this half step pattern?

I haven't found confirmation for my assumptions. I'm working on hijacking the stepper motors on an old typewriter to turn it into a plotter and the motors are 5 wire unipolar. I'll be actually hijacking the "drivers", too, which are two IC:s with 7 darlingtons and 7 diodes in each. Since it will be a plotter, I'm most interested in achieving a good resolution by having half stepping or even micro stepping work.

So the even steps would be the whole steps, while the odd steps would be the added half steps.

Correct. 5 wire steppers can all do this, but they can't do microstepping.

If I set D0 high and all others low, the motor takes one position. Then if I set D1 high and all others low, the motor rotates to next whole step. But if I leave D0 at high while D1 goes high, the motor takes the half step inbetween. What prevents from introducing microstepping here? Can't D1 go halfway high? Or is 5 wire unipolar so ancient technique that nobody bothers to develop microstepping drivers for them?

Hardly anyone bothers with unipolar motors these days; they are so inefficient.

There exist microstepping unipolar drives.

http://www.allegromicro.com/en/Products/Sanken-Products/Sanken-ICs/Sanken-Motor-Driver-ICs/Sanken-Stepper-Motor-Unipolar-Driver-ICs.aspx

But I think you would be better off ditching the 5-wire motors and just buying appropriate motors. Then you have a wide choice of microstepping bipolar drivers to use.

A very wide choice. And they are cheap as chips.

Johan_Ha: If I set D0 high and all others low, the motor takes one position. Then if I set D1 high and all others low, the motor rotates to next whole step. But if I leave D0 at high while D1 goes high, the motor takes the half step inbetween. What prevents from introducing microstepping here? Can't D1 go halfway high? Or is 5 wire unipolar so ancient technique that nobody bothers to develop microstepping drivers for them?

Yes, ancient, inefficient use of copper (much more expensive than the electronics these days!)