I’m thinking of things like waterwheels, windmills, millstones, etc- these systems would presumably have a lot of force running through them, such that stopping them for maintenance or replacement would seem difficult to do and maybe even damage the system. So what kind of mechanisms back in the day did people put in place to stop energy from moving through the machine at a given point? How do you successfully get two gears that are actively engaged to be safely uncoupled, for lack of a better word?
In: Engineering
> So what kind of mechanisms back in the day did people put in place to stop energy from moving through the machine at a given point?
You would… stop them.
A water wheel stops turning if you cut off the flow of water into the wheel. Simply diverting the water and then engaging a brake could allow the rest of the mechanism to be worked on safely and without any load.
For a windmill the panels of the sails can be removed, and again a brake applied to the main input. A millstone could be decoupled from whatever was driving it.
Brakes are a pretty simple mechanism of something pressed against the turning shaft to produce friction sufficient to bring it to a halt or keep it from moving.
You stop the source of energy that is powering the machine. It’s the same way we stop machines now.
For example, a water wheel is in a sluice, a channel where the water flows. The amount of water flowing into that channel is controlled by a control gate to keep the wheel operating at its ideal speed. That control gate can be shut entirely to stop all of the water, meaning that the wheel will no longer be pushed by water and will come to a stop. For a traditional windmill, or indeed a modern wind turbine, you can control the pitch of the blades so that they become parallel to the wind and stop forcing the windmill to turn.
So, in short, you turn off the power and you wait until the machine stops.
A clutch is a mechanism for decoupling two rotating elements in a mechanical system, and typically relies on friction between surfaces.
The safest measure is simply stopping the power source. For example watermills were often running in a “mill race” a sidechannel of a waterway that you could simply block off to turn the mill off, or windmills could simply be turned out of the wind (early designs basically had the entire mill house on a turntable with a long lever that a horse could pull into the desired direction)
> How do you successfully get two gears that are actively engaged to be safely uncoupled, for lack of a better word?
That’s the easy part, you just move the gear in the third dimension.
The hard part is getting the gear you just removed back in place.
There’s two different mechanisms you can use:
First, simply cut power. For waterwheels you can dam up or divert the water flow around the wheel and it will naturally stop spinning on it’s own. For modern windmills, we can adjust the pitch angle on the blades so that they won’t produce any torque when the wind passes over them. Once the wheel or turbine is disengaged it is usually brought to a full stop and held in place with some form of braking mechanism.
Second, use a clutch. A clutch is a mechanical device that connects two rotating shafts using friction plates. It can be engaged and disengaged even while one of the shafts is still rotating. Attaching a clutch to the drive shaft of a waterwheel or a windmill allows you to decouple the machinery that’s normally attached to it. This allows the wheel to spin freely while the internal machinery comes to a stop. It can then be reengaged to resume delivering power to the machinery.
If you take something like a water powered factory, you might have a turbine that drives a line shaft. On that shaft were pulleys that worked with flat belts of leather. On the machine, you had one pulley that was mechanically connected to whatever the machine is, and one that’s just an idler pulley, so you can slide the belt onto the idler if you want to stop the machine. The belt keeps spinning but it’s not driving the machine.
You can also turn the power off at the source, which would certainly be safer, but maybe less convenient.
Specifically for a windmill, consider that it uses a really heavy grindstone. There’s a lot of energy involved here, but the grindstone is not moving very fast. Engaging in disengaging gears is a relatively simple here compared to engines that move much faster.
Specifically for a water wheel, I visited a farm from a couple centuries ago, and that water wheel could be raised up and pulled out of the stream. In a way, this is also disengaging a gear, but without the material damage because the water doesn’t particularly damage the wheel when it starts catching.
Also, don’t forget that back in the day people didn’t do things efficiently or safely by today’s standards. A lot of things people did, they just did it and then fixed it if they ended up breaking things. There wasn’t a lot of forethought when the technology was relatively new, that came much later with lots of experience and frustration about having to constantly fix things.
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