Are you in need of green, off-grid electric energy? I have a solution for you.
Small (almost pocket size) DIY 3D printed generator.
It can be used as a hand-crank generator OR you can change the rank with a spool attachment and use it as a gravity generator.

This generator utilizes a small NEMA 17 stepper motor and planetary gearbox with a ratio of 25:1 that is mounted directly on the NEMA 17 motor.
Thanks to this ratio we are able to do around 1500rpm.

Thanks to that RPM stepper motor can produce around 25-30V and about 700mA with no load.

I'm using two small bridge rectifiers up to 2A in parallel to get more current.

Then I connected the output from those rectifiers into a variable step-down DC to DC converter with a small voltmeter and USB female port.

This is just PoC / prototype for now, but it's usable and I'm planning to make it more mobile and with more tested attachments, outputs, and many more changes that I discover along with the RnD.