Just for fun - human-powered, bicycle-based generator
On my list of speculative DIY projects is "human-powered bicycle generator". Ideally, it would be made from repurposed parts, especially bike parts (as I have a lot of those). I've finally got around to thinking about this a little more, and wonder if it is even feasible as a DIY'er with very little budget (frankly, it's not worth spending much on!). I'm an electronic engineer, not a mechanical or electrical engineer, and I get a feeling I'm a little too far out on a limb here.
Starting with the generator itself, I understood that a car alternator is not a good idea, due to the very high rpm needed (1000's of rpm). I happen to have a scrap battery scooter in my junk pile, and did some calculations on the wheel and pulley size, to determine the motor rpm at estimated max power output (which I assumed would be around 12mph). It came out as 4,600rpm! That tells me that high rpms are just part of the operating conditions of a DC generator. Are there other types of motors or generators that will run at lower rpm?
Are there any feasible ways to get this kind of rpm from a human leg-powered input? It's about a 60x multiplication! It's beyond what a chain drive can easily handle, especially one made from old bike parts. I could use an initial chain-drive stage, and a 10x planetary gearbox, but I have no idea if one of those of the right spec can be sourced cheaply.
Any musings on this topic appreciated!