Air Raid Siren

DIY Dynamic Flywheel Balancing
- https://www.youtube.com/watch?v=SkqCBcPGDEE
- TL;DW: mount it in a lathe with 3 weight attachment points, measure wobble, move weights, measure wobble, repeat till fixed.
Wooden Example
- https://hackaday.com/2013/03/31/building-a-wooden-air-raid-siren/
- 6 hole, 10 hole, two pitches.
- 600 hz is a good rough upper limit for the high pitch
- 600 hz / 10 holes = 60 rps / 3600 rpm
- hand crank can produce about 1 rps
- 600 hz / 5:1 gear = 120 holes.
- 600 hz / 5:4:1 gear = 30 holes (18 holes undertone).