Now that the rotator is complete, I built a second board up to investigate other possibilities for this design. After populating the board, I hooked up a TIVA eval board and flashed the current firmware. The power supplies were good but the motors were not switching on. It turned out that the SDA signal for the I2C bus that controls the motor configuration and current was shorted to the +3.3V, preventing the motor configuration and enabling. A few minutes under the microscope with a pick, cleared the short and the second board is working fine.