Thanks Awerby. As I feared I do not know of any 3d controller than can handle 4.2 amps. The smoothie is limited to 2 amps and the ST Electronics Eval board is limited to 3 amps. So I can only presume that high power motors are not to be used in 3d printing, unless you want to use a high power CNC controller. As for the Voltage, the inductance on the NEMA 23's is 3.8 MH. Using your equation at square root of 3.8 x 32 is over 62 Volts!! I don't think that would work on a motor rated to run at 3.78 VDC. Is my math wrong? Thanks for the help.