Earlier this summer, I came across a really interesting article about using pedal power for other applications besides just moving yourself (and maybe some cargo) down the road. The article was really long and had some complex diagrams and the takeaway, for me, was "This is pretty tricky stuff." That was mostly because I was skimming, and not the fault of the author. Regardless, I kinda dismissed the concept after reading the article.
These days, I make frequent use of a pedal-powered flour mill. Here it is, in all its high-tech glory:
Yep. That there is a very old exercise bike which, when you pedal it, turns a wheel which grinds the grain. Let's take another look at that connection:
See that complex arrangement of gears and belts? No? That's because there isn't one. The bike wheel is butted right up against the wheel of the mill, and that pressure alone (maintained by strategically placed bolts and clamps) is enough to grind the grain when you turn the pedals. I love it when the simplest solution really is the most effective.
Grinding flour this way is like riding up a hill, and the more grain you put in the hopper at once, the steeper the hill gets. I do a lot of standing on the pedals. Yet this is by far the most rewarding exercise bike I have ever used.