Haha. I couldn't illustrate my point very eloquently. MY reasoning was that the, the x brush is on the axel and the disc is rotating toward the y brush. Thats how I reasoned it in my head. I can't say for sure if this is correct, but it's the conclusion I came to.
I've had a look at some...
The disc is moving in same direction relative to the magnetic field. This creates creates a DC current. According to Lenz's law, the current will oppose the change in flux that created it. The disc is moving toward brush Y, therefore the current will flow from Y to X.