A box of surplus Vexta NEMA 23 stepper motors arrived:
The data plate sayeth:
- Model C6925-9212K
- 2 phase
- 1.8°/step
- 2.3 V
- 3 A
According to Dan, who happened into the deal, that Vexta model number applies to their custom motors, which accounts for the fact that there’s no further data available anywhere.
[Update: A National Instruments description of the motor wiring.]
Dividing 2.3 V by 3 A = 0.77 Ω windings. Multiplying 2.3 V by 2 A suggests a 7 W maximum dissipation.
Poking around with a meter identifies the windings:
- Blue – White – Red
- Green – Yellow – Black
Given those colors, the Y G B W R K color sequence on the connector doesn’t make any sense to me. Most likely, there’s a standard I’m unaware of.
The resistance from the center taps outward measures 1.0 Ω, which is close enough to 0.8 Ω for me. Measuring across the whole winding gives 1.8 Ω.
The inductance is 1.0 mH from the center tap and 4.0 mH across the whole winding. Remember that inductance varies as the square of the number of turns.
The time constant for a complete winding = 2.5 ms = 4 mH / 1.6 Ω.
That’s all I know…
The Smell of Molten Projects in the Morning 
I have the same motors that I am about to use on the Z axis of the new bot. You can press off the gear using a 3 jaw puller and a short stub of shaft to insert into the gears which you probably already measured 1/4 inch. The shaft has light ridges or knurling that just took a file to knock off using a stepper driver to spin the motor. Very nice motors and since you mentioned Dan, I know they came from the same source :)
Somewhere in the Tool Cabinet I have a little pulley puller that should do the trick. The other option is to build a complete axis drive around that specific gear… [grin]