Pendulums look innocently simple. Yet, they power some of the most jaw-dropping engineering feats we see in the modern world around us.
Tall skyscrapers that remain sturdy against the strong winds? Pendulums. Earthquake resistant bridges? Pendulums. Power stations that generate energy from waves? Pendulums.
There’s no greater way to understand this effect brought about by pendulums than by building a mechanical pendulum clock and seeing its effect come alive yourself!
The engineering principles behind a mechanical pendulum clock go beyond just the pendulum alone.
As you get into the rhythm of the swing and decide to do nothing by remaining still, you will quickly find that the height of your swing begins to diminish significantly.
Let’s now dive deeper and learn about how a pendulum clock sustains its swing!
Clock mechanisms and the engineering that drives them
You can also see the entire mechanical pendulum clock in close up action here.
Now that you know what a mechanical pendulum clock looks like, let's turn our focus to exploring each feature of the clock in greater detail, and also relating the engineering marvels around us to the 4 main mechanisms of the clock.
Pendulum
One important aspect of the clock, or rather, any clock, is to keep time well. This is where the clever escapement mechanism comes in.
This is essentially a lever that locks and unlocks a rotating drop cam profile with a number of teeth - this is what makes that tick-tock sound that you might be familiar with as a result.
The swinging pendulum is what regulates the timing of the tick-tock. That timing is determined by the length and weight of the swinging pendulum.
You can see another example of how a pendulum from the 3D printed Galileo pendulum clock keeps swinging in continuous motion.
Now why are pendulums so important? Other than just powering clocks, they actually have a much bigger role to play in our daily lives. They are crucial in rebalancing skyscrapers in some of the most earthquake prone areas by acting as a counterweight.
The Taipei tuned mass damper is one such example, where a giant pendulum resides on the top five storeys of the tower. By rebalancing skyscrapers, it helps to prevent a total collapse when an earthquake strikes, aiding in preserving the building's structural integrity.
We can also observe pendulum movements in bridges - especially in the wind and during strong earthquakes. The left and right swaying of the bridge have led to a total structural failure in some extreme cases.
One infamous example is the Tacoma Narrows bridge collapse in 1940. Since this major incident, engineers and scientists have since understood how to overcome and compensate for the pendulum-like movements, and have since developed intricate designs that deal with these external sources of energy.
Overall, by reducing resonant effects and by dampening the pendulum-like swinging of the bridge, a more stable structure can be built. One fine example is the Rion-Antirion Bridge crossing a major strait in Greece.
Weight
What does a concrete gravity train, a hydroelectric dam, and a mechanical pendulum clock all have in common? They all utilize a big weight to store potential energy a great height.
Potential energy is a category of energy that is stored; that energy can be stored in either a chemical, nuclear, gravitational, or mechanical form. It then gets converted to kinetic energy.
The importance here is knowing how to release that weight in a sustained way to drive the mechanisms that we are trying to power. In the case of a concrete gravity train, it releases its weight from the top of a hill to create power through converting potential energy into kinetic energy.
The same can be said in the case of hydroelectric dams. Except, the difference here is that the medium in which the potential energy is stored is water instead of concrete.
Mechanical pendulum clocks use this very same principle to sustain its energy in its swinging pendulum.
Power Gears
These are the gears that take energy from the falling weight in our clock, and consequently transforms the linear movement into rotational movement. This mechanism is present in the old locomotives.
You are able to see this mechanism surrounding the wheels, leading up to the internal combustion engines where the piston's linear movement is translated into rotational movement of the gears via the crankshaft.
Timekeeping Gears
Now that we have our falling weight and input gears, it’s time (excuse the pun) to translate that into telling the time; the hour, the minute, and the second hands of our clock.
We do that by having gears with different ratios that are the driven gears. I.e. they are driven by a source of energy.
We see examples of this almost every day, buried beneath in the internals of engines, turbines, and flywheels too!
Take the example of a bicycle: As you rotate the pedals with your foot, your input gear translates that energy to the driven gear. Which subsequently rotates the rear wheel.
As a consequence, changing the driven gear changes the frequency of the wheel’s rotation. The same principle occurs with the rotating hands on our clock face.
Conclusion
As you build your clock, keep questioning the principles that make it work.
The what, the how, and the why.
Only then do you really become an inquisitive engineer pondering over the mechanisms around us that we see every day.
Seeing an actual pendulum clock in front of our eyes will help make remembering concepts so much better, and it stays fresh in our minds long after the task is complete.
Remember your old childhood days when you built models out of Lego, I'm pretty sure you'll be able to recall your fond memories of those yesteryears.
In 2 weeks’ time, you might remember approximately 10% of what you read here. However, by building something and doing it, you may retain up to a whopping 90% of that activity!
Imagine being nine times as productive for the same topic, or in anything you do.
Remember that doing and teaching combined is always the best form of learning.
Happy building and keep your inner child inspired with the marvels of engineering!
- Joe, Chief Tinkerer, Puralty