From Horology magazine, February, 1939
What is the definition of and the difference between a motor barrel and a going barrel? This is in reference to a mainspring barrel.
Answer: A "going barrel" is one having the teeth on its circumference and driving the train without the intervention of a fusee. The term "motor barrel" is usually applied to that type of barrel in which the mainspring is wound by rotating the barrel itself and the power is delivered to the train by the arbor.
One of the advantages claimed for the motor barrel is that in case of a mainspring breaking the center pinion is not likely to be damaged.