I need to build some set pieces contain several very slowly rotating fans, maybe 1/4 rpm or lower for a fan with a diameter of approx 2 or 3 feet. I think the best real world example is an idle duct ventilation fan, like when you see a spy or burglar crawling through an air duct on TV or movie. the fan would just be rotating slowly due to natural air movement, not under power.
We're looking to build several of these to put upstage behind a band, and shine some strong beams of light through through them to get a cool effect with some haze, etc
Budget is an issue, so I can't go buy a bunch of real ventilation fans. they don't need to push any air, so I'm thinking about fabricating three fan blades out of some sheet material, laun, signboard, etc, then attach to a shaft (large dowel?) through some low tech bearings (speedbor through plywood?). No idea how that would work, but even if that is done, what would you power it with? I've heard people use electric clock motors before but not sure if enough torque. or maybe erector set motors (or Meccano for Europeans), but those sound expensive. I checked a few surplus websites, but didn't find anything that looked ok.
Any other ideas? I have a few week before I need to build but probably need to order parts and do a pilot in two weeks.