I’ve recently seen videos on YouTube showing gear ratios like 30 million to 1 when you spin the first gear super fast at 10.000rpm and the last gear spins so slow it would take 300 hours to spin once for example. Searching for the opposite doesn’t give any result, the highest I found was 1:625.
Why is that we can have millions:1 gear ratios but not 1:millions?
In: Engineering
We don’t have an ultra high torque source that spins slow enough to really justify a gear ratio like that, nor do we have materials that can withstand the speeds you’d end up with from the sources we do have.
If you start with one of those big cargo ship engines that spins at 90 RPM (1.5x per second) and run it through a 1:625 gear ratio then your output gear is going 56,000 RPM. If your output gear is even 5 cm in diameter then its edges are being accelerated outward at over 88,000x the force of gravity (867 km/s^2) and the teeth are moving at about half the speed of sound, and that’s just for 1:625
At around 1:1500 the teeth would be moving faster than the speed of sound in air at sea level. At 1:13,000 you’d start bumping into the speed of sound of steel and your gear would undergo some really interesting failure modes as it is unable to pass the force through itself fast enough. And this is just for a gear 5 cm in diameter, if you pick one that’s 25 cm then you hit the speed of sound in steel at just 1:2600 (1/5th the ratio)
There is no useful application for a low torque ludicrously fast gearset (there isn’t one for a high torque stupid slow one either) and you start running into issues with material properties because you just can’t spin the source slow enough. You’d need something spinning once every 12.5 days to be able to match the same gear ratio but in reverse, and you’d need an insane amount of torque on the input and we just don’t have something for that
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