This might be the p...
 

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[Closed] This might be the person to ask about gear ratios.....

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Wouldn't say I fully understand what he's doing, but found it really interesting and pretty amazing at the same time.


 
Posted : 19/05/2020 10:39 am
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That’s how SRAM are working out the size of their next, 13 speed, albatross groupset.

Disappointed ‘Take on me’ didn’t start playing towards the end.


 
Posted : 19/05/2020 10:52 am
 Spin
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Reminds me of the 'Clock of the Long Now'.

https://en.wikipedia.org/wiki/Clock_of_the_Long_Now


 
Posted : 19/05/2020 11:12 am
 Spin
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My fixie feels like it has a ratio like that sometimes...


 
Posted : 19/05/2020 11:13 am
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Just thinking about it, what would happen if you turned the last cog (with the man on it) manually? Would you be able to? Would the first in the sequence break the sound barrier? Still wouldn’t be big enough for some of the roadie heroes, mind 😉


 
Posted : 19/05/2020 12:46 pm
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Just thinking about it, what would happen if you turned the last cog (with the man on it) manually?

Maybe that's how black holes occur? 😂


 
Posted : 19/05/2020 1:00 pm
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Just thinking about it, what would happen if you turned the last cog (with the man on it) manually? Would you be able to? Would the first in the sequence break the sound barrier? Still wouldn’t be big enough for some of the roadie heroes, mind

The short answer isn't you couldn't, far too much friction.

But just for fun lets assume a frictionless universe.

Now the little lever on the end of the first axle (the one that is turning at 375rpm near the start of the video) Lets say its 1cm long with a mass of 1 gram. This means when its horizontal its producing a torque of .00001Nm due to gravity so you would need to generate at least this torque to turn it through 360 degrees.

So when we turn our man at the slow end it needs to be able to produce 10^-5Nm at the fast end. But we have a gearing reduction of 10^100!
So we need 10^95Nm to move it.

That would mean a mass of 10^94kg on the end of a 1 metre lever.

10^94kg is quite a lot (its about 40 orders of magnitude more than estimate mass of the observable universe)

So a handier mass might be better. The earth's mass is 6 x 10^24kg so if it was on the end of a lever roughly 10^70m long it would work. Unfortunately this is quite a few orders of magnitude bigger than the observable universe.

You could try the Sun instead - it's a good deal heavier than the earth but you would still need a lever massively longer than the observable universe and you would probably burn your hands too.


 
Posted : 19/05/2020 1:55 pm
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But just for fun lets assume a frictionless universe.

Now the little lever on the end of the first axle...

Brilliant!


 
Posted : 19/05/2020 2:03 pm

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