ifugaopapercraft:
Yes, the servos do move but only momentarily. Previously they would continue moving until the viewer moved a distance away, then stopped. Everything seems to be happening just one time rather than continuously while the sensor value was within range.The motor runs without stopping, regardless of sensor readings.
I was working on the stepper drivers when these other calamities occurred. I'd like to resolve them before connecting the steppers.
Why do you believe the serial monitor displays only a few values, then stop?
Because something is not working 
I would suggest commenting out three of the four functions in the if and tackling them one at a time.
I reiterate my note about the functions running in sequence. First the servos will twitch, then stop. Then the motor will start. Then the unipolar stepper will do a sweep, and stop. Finally the bipolar stepper will step once, and once only. Next time through the loop the sequence will start again (but as the motor's already running, it won't start running again).