I worked for a company back in 2009-10 that was trying to make giant (8ftx12ft ish) LED billboards by using 6 spinners with LED arms that overlapped (IYSWIM.)

I worked for a company back in 2009-10 that was trying to make giant (8ftx12ft ish) LED billboards by using 6 spinners with LED arms that overlapped (IYSWIM.) Only saw it spin up once and it terrified me - all the wheels had to be chain-linked and -driven because they'd tried keeping 6 motors synced up at the same exact speed whilst spinning round hefty 4ft propellors and it just led to the arms hitting each other and "rapid unscheduled disassembly" - not what you want for your roadside adverts. They also made huge cylindrical ones that were actually deployed at a few places in London and around the UK. Never really took off because the mini-PCs inside[1] tended to shake themselves to bits after a few months of spinning around at 4000rpm. [1] I obtained my first Mac Mini from them free because they'd tried that in a cylinder, the hard drive Did Not Like It, and they were just throwing it away.