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 make it possible to have a real working clock made of LEGO!

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 video shows the improved escapement that should eliminate the issues shown in the previous video.

This clock operates similarly to most mechanical pendulum clocks:

The escapement is a grasshopper 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 1.6 cm/hour, for a power consumption of about 25 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.

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.