Rather by accident, I have made a few of these vertical-axis, bike-powered carnival rides now.
The first one was the Flanger, which is pronounced "FLANG-er" (rhymes with "clothes hanger"). It's a portmanteau of the words "fling" and "hang". It was commissioned by the Corvallis Bicycle Collective. The second one, the Velocopter was a false-start project for a customer. Somebody named Lena suggested the name, so thanks to her! Ultimately, business dealings fell through, due to my own flakiness, but I now have an improved version of the Flanger, that seats four people and is generally beefed up.
Power is transmitted from the riders to the center drive mechanism by a simple hydraulic circuit. The Velocopter has somewhat lower gearing and has an inline oil filter, which reduces its speed relative to that of the Flanger. The Flanger really has that "pseudo-imminent-danger/adrenaline" feeling to it, whereas the Velocopter is more sedate.
Currently, it's sitting out in the rain in my back yard, so if you want it, let me know, I'll make you a good deal. It also has an alternator attached to one of the bikes that ostensibly powered some LED strip lights, which only ever worked intermittently. Not sure what the deal was there. Probably just needs the wires wiggled.