Re: Power Supply Voltage
The drivers will drop the 70V down to whatever the motor needs, but will produce more heat as a result. Watch them carefully and reduce power if they get too hot.
I think you will need more current, but could be wrong. Try it and see.
I like using batteries. A stack of 4 12 volt motors in series with a 48 volt "cart" charger and a nice set of fuses would do you good.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)