I've hooked up the new power supply and both of the mounted motors to the stepper drivers, and the Arduino to a solar powered (!) USB power supply. Pins 4 and 5 drive one stepper and 6 and 7 drive another, with the standard test program that merely moves back and forth. And the Y stage moves! Happily, happily back and forth. The X stage, not so lucky, the tubing is not tight enough to move the weight that's on there, so I'm currently glueing it on. Should be ready to run tomorrow evening.
Issue 1: The wiring is flimsy at best. I need some jacks that fit the Arduino, and maybe a little board that I can mount the various things on so they're less random. Just mounting the drivers next to the motors would help.
Issue 2: After 10-30 seconds of power, the stepper drivers start to stutter audibly, whether actually moving anything or not. I suspect the power transistor is getting too hot and starting to flake out. It certainly gets hot. I thought my heat sinks would be enough, but maybe not. Must go to Aarhus Radio Lager and get better.
Issue 3: As I mentioned, the X stage coupling is not tight enough. Not sure what the best way to make it be tight and stay tight is. Maybe just tie a lot of string really tightly. Or tie some string that will shrink when wet.