Practical LEGO Pendulum Clock

November 2017 ยท 4 minute read

This LEGO pendulum clock is truly practical to use as a clock: it runs for over 72 hours or 3 days, it is very easy to rewind in just a few seconds, and it can be accurate to within a minute per day. A screw on the pendulum bob allows precise adjustment of the effective length of the pendulum. The hands can be easily moved to set the time. These features all contribute to making it possible to have a real working clock made of LEGO requiring only a few seconds of rewinding every 3 days!

LEGO pendulum clock

This video shows how the clock works, and shows what some of the parts looked like after running continuously for about one year.

This clock operates similarly to most mechanical pendulum clocks:

The escapement is a Galileo escapement built around a 40 tooth gear as the escapement wheel.

Closeups of the escapement

The knob on the pendulum bob allows the effective length of the pendulum to be precisely adjusted, enabling very accurate time-keeping.

The clock is driven by a 560 gram weight hanging on a chain, which falls 1.9 cm/hour, for a power consumption of about 29 microwatts. To rewind, simply lift the drive weight. The chain drives a freewheel, which allows the chain to be pulled freely through the clock in reverse. The freewheel rewinding mechanism has minimal friction while the drive is engaged, unlike my previous designs that used a differential with a one-way ratchet. The freewheel is also more reliable than my ratchet designs.

Pendulum bob and drive freewheel

The chain is a loop connected back to the bottom of the weight, to maintain a consistent drive force by balancing the chain.

Here is an file and building instructions for this clock. There are some differences not shown in the file or instructions:

If you do attempt to build the clock, here are some additional tips and comments:

If you want to see more LEGO clocks, check out David Ziemkiewicz, Ben Van de Waal and KEvronista on YouTube. The idea for a knife edge pendulum suspension comes from their videos, and they have a lot more cool clock videos to see.