Automated Pendulum

The pinnacle of 17th century technology…

Introduction

Since it was explained to me how pendulum-based mechanical clocks work, I’ve had the idea bouncing in my head of an “automated pendulum”.

We’ll get to the physics lesson later but quite simply, the swing of the pendulum controls the tick-tock of the clock. So, if you want your pendulum clock to keep time accurately, the pendulum has to take a specific time to swing left and right. Now, one can monitor one of these clocks and periodically manually adjust the pendulum but that didn’t seem fun to me. I wanted all the charm of an old clock with the accuracy of something modern.

So that idea wallowed in my brain for a few years until last week, when I came across Hackaday‘s One Hertz Challenge:

One second. Sixty of them in a minute, 31 million in a year, and maybe two-and-a-half billion of them in your lifetime. Turn the second over on its head and you’ve got the pace of a relaxed human heartbeat.

For this challenge, we want you to design a device where something happens once per second. How accurately you pace the beat, how absurd the display, or how diabolical the mechanism behind it all, we want to see it. Let your creativity run wild, as long as something happens at that most fundamental of all frequencies.

A device where something happens once per second. Like clockwork.

LIKE CLOCKWORK OMG

I SHOULD BUILD THAT AUTOMATED PENDULUM THING!

A short view back to the past…

Three hundred and 69 years ago, this dapper chap invented the pendulum clock, taking clock accuracy to new highs. Quoting this paper, “Before Huygens’ invention of the pendulum clock, typical clocks (e.g., verge escapement with balance wheel regulator) varied by approximately 15 minutes (1%) per day (Landes 1983)” and, post Huygens’ invention, “well-adjusted pendulum clocks of the 1660’s would typically run at rates which differed by only 15 seconds per day”. Neat.

Pendulums, how do they work?

There’s a bunch of physics and maths regarding pendulums and, if you want to explore it, here you go.

However, to understand the basic principle, just watch these videos:

Length actually matters

Swing swing swing.

(Optional) Listen to this song by Pendulum: Propane Nightmares

Parts List (with costs @ 18/08/2025)

Purchased:

1. 5V 4-Phase Stepper Motor (28BYJ-48-5V) – R29.00
2. ULN2003 Stepper Motor Driver Board – 5 – 12V – R16.00
3. TR8X2 Metric Lead Screw Only – 200mm – R45.00
4. TR8x2 Metric Lead Screw Nut – R19.00
5. Flexible Aluminium Coupling (5mm/8mm) – R23.00
6. IR Breakbeam Sensor Module – R18.00

From my parts bins:

1. Raspberry Pi Pico W
2. Jumper Wires
3. Breadboard
4. Wood

Software Used

1. Thonny – v4.1.6
2. MicroPython – v1.24.1

Other Requirements

1. Soldering Iron + Solder
2. Screwdriver/s
3. Mechanical Clock Movement

Hardware Setup

Take it away, me:

Software Setup

For the sake of completeness, I have posted the code on GitHub. Please do not run this code. There are numerous ways that I would want to improve it but alas, I was operating on a tight schedule here. At some future stage it will be beautiful and elegant and bug-free but that day is not today (or tomorrow or anytime soon :)).

Thoughts + Conclusion

It (eventually) worked! It’s very rough and I wouldn’t let it run without supervision but that’s the nature of a PoC build. It was fun using a stepper motor and breakbeam module, parts that I’ve not had the pleasure of using before.

I did fail to build a seconds pendulum but I’ll rectify that when I have access to an appropriate movement that can drive such a pendulum.

Special thanks to Devan Moodley of Prestige Watchworks who lent me the clock movement (at very short notice) and fixed the suspension when I broke it. If you need a watch or clock serviced or repaired, email him or DM him ASAP!

Here’s the final demo of it working and a quick overview:

The Future

I want the next version to have a seconds pendulum so Automated Pendulum v2 will require me to acquire and then defile a nice grandfather clock. Imagine a grandfather clock with a pendulum that needs power and could have bugs in it’s firmware. The horror. But then also imagine the potential accuracy…

Anyway, here’s my wish list for v2:

• Aesthetics
• Better timing (Maybe a GPS receiver with PPS out?)
• Long term time correction (control the pendulum to optimize for overall clock accuracy)
• Wireless (all electronics built into the pendulum with wireless power using eg. Qi)
• etc etc!

If you have any questions/would like to share your experience with automated pendulums, leave a reply below. To receive an email when I publish a post, subscribe here.