Hand Crank Generator for USB-Devices // USB-Kurbelgenerator

I got the inspiration for this project from an excellent video by the ingenious Robert Murray-Smith. I implemented the electronics exactly as described there - except that I also added a voltage regulator.

This small handheld generator can be used to charge USB devices in the event of a power outage without having to rely on sun or wind.

A stepper motor is used as a generator. In one version I used an original stepper motor for Artillery 3D printers, in another a cheap no-name motor that is structurally similar or possibly even identical - at least there are no relevant differences neither visually nor in the output.

The gearbox consisting of 3 gears has a ratio of 1:4.5, which allows sufficient cranking at a comfortable speed. However, if the gears are printed imprecisely or the printer is calibrated differently than mine, the gears may seize or jam when turning. Depending on the extent, this can be remedied by "sensuous" cranking past the blocking point. After a long period of cranking, the wheels then adapt well to one another due to the desired abrasion and allow smooth cranking. In any case, greasing the gearbox is recommended. Since nothing else was available, I used silicone grease, which made cranking considerably smoother. I cannot judge to what extent the grease is suitable for use with PLA in the long term and whether there are better alternatives.

In order to be able to use a compact housing, I didn't build the electronics on a circuit board, but soldered the components directly on top of each other. I hope the pictures illustrate exactly how I did this. 

It is important to set the output of the voltage regulator to 5V before use. I was able to set this relatively precisely in advance by connecting a 9V battery and measuring the voltage at the output.

Printing recommendation:

Gears: Initial horizontal layer expansion: -0.25mm

Gears, crank, USB cover: layer height 0.2mm, first layer print speed 5 mm/s. Print bed adhesion: Skirt

Housing parts: layer height 0.3mm, print speed of the first layer 25mm/s, print bed adhesion: Brim!

Crank: Support required (all other parts do not require support as long as the line width is not smaller than 0.4mm and the layer height is chosen as specified above).

The crank is printed-in-place. The cylinder sleeve at the end of the crank must first be loosened by carefully breaking the lower edge in order to be able to rotate. If this does not work because the sleeve is too tightly connected to the crank, a lower flow setting should be tried.

Parts List:

1 Nema17 stepper motor 48mm, 12V, 2A

2 x 4 diodes 1N4001

2 electrolytic capacitors 2200uF, 50V

1 voltage regulator (buck converter)

1 USB type A charging socket

10 Screws M3*4

6 threaded inserts M3x5.7x4.6

The connection cable supplied with the motor can be used for the wiring. To connect the USB socket to the voltage regulator, I made two cables with Dupont connectors and connected them to the angled pins previously soldered to the voltage regulator.

Depending on the crank speed, this generator can supply approx. 0.4 A or higher. However, this depends heavily on the device to be charged and the charging cable used. It was not at all easy to find a USB device in my household that requested higher current.