When I ordered my stepper motors sometime last year from motion control products I chose the cheapest model at £11.23 which was FL42STH38-1206A sometime afterwards I realised that these steppers have much lower holding torque than the recommended mendel FL42STH47-1684A-01 (25.5N-cm vs 43N-cm) however this was not a major problem since mendel requires that “Torque must be at least 0.13 Nm” which is 13N-cm, and well below the rated holding torque. It was only when I came to wiring the steppers up that I came across the next problem. The Generation 3 stepper drivers are for use with Bipolar steppers.
Wheras the steppers I had bought were Unipolar steppers.
Fortunately for me they were 6-wire Unipolar steppers, and as you can see from the wiring digrams above you can just not connect the centre taps for the coils (labeled A and B above) and we have a bipolar stepper again.
More recently when I decided it was cheaper and simpler to use two steppers for my Z-Axis, I was a stepper short. This time I bought the SY42STH47-1684B compatible product from Zapp Automation for only £8.50 it has a holding torque of 43.15N-cm and is a 4-Wire Bipolar stepper. I am going to use this to drive the CrudeStruder, as I think it could benefit from the extra torque.