I taught Electricity, Woods, Drafting, and once, Auto shop. That was the time I backed up and leaned against the newly greased lift and put an oil slick down my back!
On my video I counted 16 rotations in 24 seconds, so the would be 40 RPM... I like the faster speed but you can guess that half as fast = 20rpm, etc.
The screwdriver was advertised at 100rpm. But, I used 1 battery instead of 2 so I would have figured about 50 rpm.... only off by 20%!
Ed
ps. how about a rubber roller on a motor that spins the edge of the beacon. The motor would be offset and not interfere with the lighting?