I kept running into this problem with the stepper motor. One second it works — I fixed it! Then a minute later it stops — I broke it! It seems that the lesson I learned is that when you have this happen, It’s usually a power issue.
Eric Rosenthal to the rescue.
Ok, so my circuit wasn’t supplying enough power. So, I with Eric’s suggestion, I switched to a Sparkfun EasyDriver and used this “Boost Converter” circuit to feed into it. That way, the Battery that supplies 6V can “Boost” up to 12V, then the EasyDriver can supply 5V to the YUN.
Voila! More power to my motor!
**** When I switched from the Adafruit Motor Shield to the SparkFun Easy Stepper, I realized that the motor would not go backwards. It’s because the two boards expect the motor’s wires to be in a different order. If this happens to you, double check your wires!