I've got a PM2515-03 stepper motor and the ratings are 5V 0.5mA. I use the 5V output from the Arduino with a 10ohm resistor.
If I use those ratings, and I attach a small wheel to it, any tiny amount of force to the wheel makes it stop and vibrate. So like if I hold the motor by its attaching wires and let the wheel roll on my table, it just gets stuck.
But if I use a 1ohm resistor instead, I essentially am putting 5A through it, according to ohm's law. And if I do this it runs perfectly and it doesn't get stuck. Granted it does get slightly warm.
I'm just a bit confused as to the ratings, as it seems what is suggested can hardly hold any force.