Here in Russia people sell stuff on the commuter trains. So I once bought this really cheap hand cranked flashlight for 100 rubles (~$3 US). It worked just fine. I had to take it apart. Inside there were two 3 volts batteries in series, meaning that the dynamo inside the unit generated about 6 vdc. I immediately soldered a usb cable and made this into a hand crank charger for my Android phone.
Here are some pictures of flashlight being taken apart and a USB connector being soldered to it. To figure out polarity and how to propperly connect the usb line I read this page: http://pinouts.ru/Slots/USB_pinout.shtml
I then tested the unit and took this video: