One area regarding step motor drives seldom discussed is a means of shutting off or at least significantly reducing drive voltage when the motor is stationary. Normal hysteresis will help keep current flow down while stepping, but once the motor has been stopped by simply not stepping anymore the current through the energized drive circuits will cause tremendous heating of the motor and or possible destruction of the drivers themselves. I have seen quite a few designs that use a heavy duty single pole relay to switch the drive power off and other designs that use a high side mosfet for the same purpose. Using the mosfet does offer the option of using PWM to hold the motors locked when not stepping to prevent the load from moving the motor and still limit the current when stationary.

Hal