How does a mechanical watch works without having any batteries?

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I have my interests in watches.

In: Engineering
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With a spring. Mechanical watches have a spring that gets wound up, thus storing energy. As it unwinds, it releases that energy through a series of gears to allow watch to tick at a steady and correct rate. As the spring unwinds, it loses energy, so you have to manually rewind it again periodically to keep it working.

Well let’s start with what is a watch and what does it do?

A watch on it’s face (ha) is just a device that takes energy and gives you an accurate time. You see the face, which usually has two hands and probably a date, if not other complications.

Inside the watch, you have 3 basic things: a place that stores energy, a thing that vibrates in a certain way and a way of taking those vibrations and driving the hands with them. This vibration is there because that part only vibrates at a specific rate, called a resonant frequency.

In a quartz watch, (the type with a battery) The battery stores the energy, a small piece of quartz vibrates (piezoelectric oscillator if you want to look beyond an ELI5 level) those vibrations are counted by an electric circuit which drives a stepper motor, turning the second hand, and through gears, the minute and hour hands as well as the date ring.

In a mechanical watch, the energy is stored in a spring called the mainspring. The vibrating part is called the balance wheel, a perfectly balanced wheel with a smaller spring that tries to keep it in one place. The spring doesn’t have a lot of force, so if you give the balance wheel a little push, it’ll swing one way, then back the other, and if you give it the same size push every time it turns, it will stay at the same frequency, or rate of vibration. The part that does the pushing is called the escapement. It’s usually a rocking device that allows the escape wheel to advance only a certain amount each vibration (usually 4 or 5 times per second depending on the watch).

Now that we have a repeatable, accurate vibration, you attach the hands and other continuous complications to the gears that are doing the pushing, and you have a watch. There are a ton of other complications some high end watches have like Tourbillons, Minute Repeaters, Perpetual Calendars, Chronographs, and Dual Balance Wheels. Grand Seiko even has their weird Spring Drive movement which uses a mainspring to drive a quartz oscillator.

One more thing I’ll add is that for a mechanical watch, you will wind the mainspring by hand. For what’s called an Automatic watch, you can usually wind the mechanism by hand, but the watch has a special piece that can wind the mechanism for you called a rotor. It’s a piece of metal that is weighted on one side so that it spins around as you walk and sway your arms. These can stay wound as long as you wear them for at least an hour a day.

Here are a couple videos to see how the pieces work:

TL;DR Video: [https://www.youtube.com/watch?v=3MUL65-vZHY](https://www.youtube.com/watch?v=3MUL65-vZHY)

More involved old school video: [https://www.youtube.com/watch?v=rL0_vOw6eCc](https://www.youtube.com/watch?v=rL0_vOw6eCc)