Mobile phone is an essential tool of communication nowadays. Not only it can be used to connect with friends and family but more importantly to call emergency services in life threatening situations. We want everyone to be able to make a call even when there is a power outage, so in this paper we present a detailed instructions on constructing a portable hand-crank phone charger. We use as many 3D printed parts as possible, and describe explicitly all the calculations done, so that a person with no engineering background can assemble a similar device. Calculations include the required input rpm and gear box ratio determination. The final device has a common USB type A output, being capable of charging any modern smartphone.
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Slutskiy et al. (2024) studied this question.
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