I decided to re-design the turbine at the last minute, since the parametric design was a little too complicated to do on the timeline I need to do it in. I still want to try it out, but it'll have to wait for later. But in the process of designing something light and cheap and easy to make, I hit on a much simpler, and apparently effective design!
This design only uses a single sheet of coroplast- around $12 in material. I twisted the parts in sketchup, and then made cross-sections for the top and bottom, and cut out the parts on my partner's Glowforge (she makes laser-cut jewelry for a living).
I had originally thought that I would sort of sew the top and bottom plate together with wire, but that ended up being pretty tedious, and after play around with the parts a bit, also turned out to be unnecessary. I ended up not using the bottom plate at all, and just used the slotted one. The cuts are accurate enough, and the coroplast is flexible enough, that I could just slide the turbine vanes through the slots, and they would stay press-fit in there.
This had not been my intention, but what ended up happening is that since the coroplast vanes are twisted and under slight tension, when you align them in a circular array, they end up creating a sort of reciprocal "tensegrity" effect, where they are all pushing out against each other, which makes the turbine remarkably strong and sturdy for it's weight (less than 1lb). I dropped it from about 7 feet twice by accident while figuring out how to mount it, and it was fine- it just kind of bounced.
I used a gear I had laser cut for a failed prototype earlier in the project, and wedged it into the top of the center tube. This was an inelegant hack, but worked surprisingly well. I'm using a NEMA17 stepper motor as the central bearing- since I need a bearing anyway, and the stepper will produce a bit of power. The neat part about doing it this way is that the power is produced on the rotating part of the turbine, not on the fixed pole.
This lets me hook the stepper motor up to some copper "fairy light" style LED strings, and wrap them around the turbine. When the turbine spins fast enough, the LEDs light up and strobe directly from the low-voltage AC power produced by the stepper- visualizing power output with light. The RPMs required for this to happen are still higher than I would like, but it does happen, and that also makes it kind of special, like an achievement to be unlocked.
I'm hoping that when the gas mantles are on (did I mention I got the gas mantles running on trash-gas), the hot air will push out the top of the lamp and out through the lower vanes, causing the turbine to spin- eventually fast enough to light up the LEDs. If that works, then the effect will be that as the Metabolizer heats up and starts producing gas, the gas mantles will start to glow brighter and brighter, the turbine will start to spin, and then the lights on the turbine will begin to fade on, a swirl of strobing points of light that get brighter as the turbine spins faster- hopefully to dramatic effect...