We started off experimenting with the Adafruit Shield and the JK57HS51-2804 bipolar stepper motor. However, these motors asked for 2.8A per phase at 12V, and the Adafruit shield could only provide up to 600mA continuous per motor, with 1.2A peak current. Moreover, the motor controllers on this shield are designed to run from 4.5V to 25V. Hence, these two items were not compatible with each other. Given the fact that any movement towards 1A would require a heatsink to be positioned on the motor driver, we decided to use a new bipolar stepper motor, NEMA 17, that required 350mA at 12V with 200 revolutions per step.
One Adafruit shield drove the xy-plane, while another one drove the AIRPO DC pump to pick up pieces and a servo motor to move in the z-axis.