"Fidget spinners" are all the rage at my school; ever since they got a 3D printer the students were allowed to use, people have been printing hundreds of these little trinkets, with one skate bearing in the middle to make it spin & three more as weight to increase the inertia. (The picture to the left is an example of one.) People have been "battling" with them like Beyblades by hitting a finger against the side and timing the spin. That's not an objective enough test for me, so I'm building a machine that spins them up for a constant amount of time & times how long they take to come to a complete stop.

Video:
https://www.youtube.com/watch?v=CbrzxCJNXjo
(Video stabilization totally messed this up)