Thank you for contacting National Instruments. In theory, analog feedback for stepper motors should work correctly; however, there are several problems that will arise when you attempt to control a stepper motor from an analog feedback. In this type of system, the analog feedback is converted into a position and compared against the desired position, and then the stepper motor is "pulled in" to that position. One of the problems with analog feedback for stepper motors is noise. With a servo motor, the PID algorithm takes care of the noise. But you cannot use PID with stepper motors. The noise in the signal can cause problems like stepper motors "shaking" because they are stepping back and forth between two positions because of the noise. Another possible problem, a
lso caused by noise, is "sliding". This is where the motor continues to move in one direction after its original move, because it is only responding to either the positive or the negative error. The final issue that causes problems is the calibration required to correspond the voltages with a given position or number of steps of the motor.
Because of these issues the stepper motor is not recommended or fully supported on stepper motors. If analog feedback is required for your application, then I would recommend adding an encoder to read the position also. You can also use the analog feedback by reading it into an A/D channel on your board, and handling the values in software as needed. By doing this, you can even develop your own control loop programmatically based on the voltage that you have read.
