Again, a motor driven with such a rudimentary drive method will have terrible performance!

As a test, take your 5V motor, use it with the ULN28xx system but use 24V as the supply voltage. I Googled the model number and found a figure of 60ohm phase resistance which would equal a current of 83mA. With a 24V supply you need to insert a 200ohm >2W resistor in each of the four wires going to the ULN chip.

If you don't have any power resistors at hand just take a bunch of ordinary 1/4W and parallel (or series) them up. 10 2k 1/4W resistors in parallell will be 200ohm 2.5W for example.

For reference, my bipolar NEMA34 motors are rated at something like 2.7V, 4.5A. I'm running those with bipolar drives from a 65V supply. Had I used a 2.7V supply their torque would fall off so fast they'd be unusable.

The motor will get warm, with or without a load - that's just how they work. A DC motor for example, running unloaded, will only PULL as much current as is needed to overcome the friction losses of the bearings and brushes etc. With a step motor you are PUSHING the motors rated current into the winding(s) (or at least you're trying to) no matter what the actual load on the motor is.

Look at Roberts link or Google Jones on stepping motor (or something like that).

/Henrik.