Need help distinguishing between unipolar and bipolar 6-wire motors

I got some nice steppers and driver/controllers from an old printer. Most of the motors were 6 wire and worked fine Easydriver (after identifying correct pair of leads). Still, there were significant number of unipolar drivers/controllers and found out that at least some of the 6 wire steppers were actually unipolar. Here is one: http://qzwellrich.en.alibaba.com/product/1770394445-221076559/Stitch_density_stepping_motor_42D2077.html. Please advice:

1) is there a way to differentiate unipolar and bipolar 6 wire motors without a spec sheets? 2) is there an advantage of running unipolar stepper by unipolar driver/controller (as opposed to running it as bipolar)? It would be ideal if I could reuse some of these drivers/controllers. thanks.

P.S. The driver is STK672-110 - Unipolar Fixed-Current Chopper.

P.S. I am using these to build a small CNC, eventually, but right now just trying to get a hang of it. thanks.

If every wire is connected to every other wire, it's unipolar.

If wires are connected in sets of three you can wire it as four-wire bipolar or five-wire unipolar. Each set of three will have two pair that show resistance X and one pair that that shows resistance 2X. The 2X pair are the unipolar ends and the remaining wire is the center tap. Connect the two center-taps together for 5-wire unipolar. Ignore the center taps for 4-wire bipolar.

Hi John, thanks for the reply. Here is some more clarification:

the pin connections are the following: the following two pairs (1-2) (5-6) both 4ohm (between the pins in the parenthesis, not across: not between 2 and 5) the following pairs (1-3) (2-3) (4-5) (4-6) have 2ohm. there is no other connection between the leads not listed together in the parenthesis.

Thus, 3 is a common for 1 and 2. 4 is common for 5 and 6. this is a typical bipolar setup so far and, as I mentioned, it runs fine with 1/2-5/6 on easydriver.

what I cannot figure out how to tell that this is actually is unipolar (although it can be ran as bipolar)?

Assuming that the site I pointed out did not have an error and this is not actually a bipolar, second question was: is there an advantage of running unipolar stepper by unipolar driver/controller (as opposed to running it as bipolar)? It would be ideal if I could reuse some of these drivers/controllers.?

And, one more question since we are here: Why do manufacturers put 6 wires if we only need 4 to control bipolars? Is there another (or more advanced and efficient) way? thanks.

Unipolar has the advantage of only needing a unipolar driver, like a simple MOSFET, on each pin. Bipolar needs bipolar drivers (a way to reverse the voltage like an H-Bridge) on each coil. I don't know if one is more efficient than the other. Maybe Google would know.

OK. thanks. I googled the daylight out of these with little success. :)

so, I guess, there is no rule of thumb for differentiating the unipolar from bipolar steppers with 6 wires...

so, I guess, there is no rule of thumb for differentiating the unipolar from bipolar steppers with 6 wires...

Why do you want to make a distinction? Essentially all 6 wire motors can be used either as unipolar or as bipolar, with no connection to the center taps. The only exception I know of are three-phase, six wire motors but they are very rare.

If the windings are low impedance you will want to drive it current-controlled, treat as for any other bipolar with chopper drive.

High impedance windings mean a fixed voltage drive either as unipolar or via H-bridge is OK, but you accept the limited performance of a high-resistance motor.

Low impedance typically 0.2 to 5 ohms, high impedance typically 20 ohms or more.

The only reason why this question came up because the manufacturer classified this as unipolar and there had to be some reason for this. I have other motors with similar wiring that are classified as bipolar (6 wires total with 2 pairs and a common for each pair).

I am just curious if there is a reason why manufacturer classified it as unipolar and if I am missing out something by not running it as such.

mvoltin: I am just curious if there is a reason why manufacturer classified it as unipolar and if I am missing out something by not running it as such.

Who knows? Its a six wire motor with a certain current rating and winding resistance/inductance, that's the real identity of the motor - whether you drive it voltage or current driver, bipolar or unipolar is your decision, though there less sensible and more sensible options given the performance you want and the money you have...