To the best of my knowledge, the voltage on the pins is fixed. You can turn them on or off, but you don't get to say what the voltage is. Anyway, stepper motors aren't driven by variations in voltage.

I'm wondering whether you'd need to use something closer to the bare metal, like C. You would otherwise likely have some problems getting the timing right, which is critical.

From what you're saying, I'm thinking you aren't talking about stepper motors, but rather ordinary servo motors.