Comment by londons_explore | Hacker News Reader

Comment by londons_explore | Hacker News Reader

londons_explore

I have often wondered if ideas from a buck/boost converter could be applied to a mechanical gearbox. Voltage and current in electrical circuits (where voltage x current = power) is completely analogous to torque and speed in mechanical shafts (where torque * speed = power). Every electrical component has a physical counterpart. Spring = capacitor. Inductor = mass with momentum. Resistor = friction brake.

The goal would be a variable ratio gearbox using a fully mechanical system, using a spring and a hammer type mechanism to convert one torque/speed to another torque/speed.

This is already done in impact wrenches, but I would hope that rather than having an impact rate of say 5 Hz, you have an impact rate of 50 kHz or more, allowing a smooth conversion from one speed to another.

Obviously, the difficulty is in the details - designing parts to withstand 50k hammers per second for years of operating without failing from fatigue.

Various other mechanical things already operate at high mechanical frequencies. SAW filters vibrate things mechanically at Ghz and don't suffer fatigue failures.

You're overcomplicating it; you only need a single clutch and in/out springs[1] to do this. If you're spinning at 4000 rpm and your springs cover 6 degrees of rotation, then your clutch needs to be able to actuate at 4000 Hz.

When the clutch is engaged, the engine-side springs compress to supply the torque and match the speed difference. When it's disengaged, the springs expand back out as it returns to engine speed. The obvious problem is that clutches do not smoothly click on and off like a transistor.

However there are more specialized devices that use stick-slip dynamics like piezo actuators. Since there is a much more rapid transition between "on"/"off", they can be very efficient and allow relatively weak devices to exert very large forces. They're just only able to take very small steps.

[1] Labeled 4 here: https://haynes.com/en-gb/sites/default/files/styles/blog_lan...

> When it's disengaged, the springs expand back out as it returns to engine speed.

What is it?

I think you need an intermediate flywheel, with springs and clutches on each side. The intermediate flywheel's mass is tiny, so might be formed by just the masses of the springs and clutch mechanism.

It is the clutch. The clutch is your flywheel; it's free floating and connected to the driveshaft with springs. When its engaged, it is connected to both shafts by springs. When it's disconnected it's only connected to the driveshaft by springs.

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