Velocity of the centre of a small cylinder is v. There is no slipping anywhere. The velocity of the centre of the larger cylinder is

In figure, C1 and C2 are IC (instantaneous centre of rotation) of the two cylinders. The cylinder can be considered as rotating about C1 and C2. In the absence of slipping between the plank and the cylinders, points A1 and A2 have the same velocity. Angular velocity of the larger cylinder ω = 2v4R=v2R.vCM=(2R)v2R=v