Consider an ideal fidget spinner, composed of a central disk (a bearing, usually) plus some N disks, all of them of radius L distributed regularly with their centres along a circle of radius R. In the simplest case all of them have the same mass, M, and are able to turn freely without resistence. The central disk constitutes a pivot, attached to some fix equipment in a way parallell to gravity field, so the whole problem is one of rotations in a plane. Plus, the symmetry of the problem makes that total angular momentum is preserved. I think that some interesting problems could be proposed in this setup because it goes a little beyond the simplest planar rotation but, not having external force field, is is still simpler than other articulated problems as the double pendulum. So perhaps this thread could aggrupate them. A first question: percussion. If with start the spinner with a single impulse [itex]F \Delta t[/itex], applied say at a distance R+L of the rotation center, so that we transmit a total angular momentum [itex]F \Delta t (R+L)[/itex], ¿which will be the rotational speed of the spinner? ¿will it be the same if we block the disks so they are not able anymore to rotate freely?