I want to make a small mechanical generator, what should I prepare?

Oh! Your idea is a little outdated. When primary battery technology was not yet available, a large number of toys, clocks, etc. were used. were powered by mechanical springs. But now there are all kinds of batteries in front of us, and their volume ratio, weight ratio, capacity ratio, price ratio, etc. are different. All aspects of performance are far superior to mechanical power. Therefore, unless you want to experiment or experiment with the following mechanism, in terms of real practicality, it is better to use batteries.