Red ribbon wound around a red spool (above) is taped to blue ribbon wound around a blue spool (below). The ribbon is essentially massless, but the solid cylindrical spools each have mass m and radius R. If the red spool can freely rotate on a fixed axle and the blue spool is positioned directly underneath with the ribbon taut, what is the downward acceleration of the blue spool? Gravity is downward.

Question

Red ribbon wound around a red spool (above) is taped to blue ribbon wound around a blue spool (below). The ribbon is essentially massless, but the solid cylindrical spools each have mass m and radius R. If the red spool can freely rotate on a fixed axle and the blue spool is positioned directly underneath with the ribbon taut, what is the downward acceleration of the blue spool? Gravity is downward. 
Enter your answer in terms of some or all of the variables m, R and g.