SP7: Electromagnetic Pendulum Desk Clock

This clock is my first battery powered pendulum clock. It uses a simple electromagnetic driver circuit to impulse the pendulum. Preliminary measurements estimate that the clock should run for over a year on two AA batteries.

The overall size was determined by the pendulum length with a half second period so the second hand would have 60 ticks per minute. The clock is 11.2" (284mm) wide, 13.8" (350mm) tall, and 5.9" (150mm) deep. This makes it larger and more impressive than the SP6 stepper motor desk clock. Total print time is around 70 hours using about 1kg of filament.

The clock was originally designed to fill the complete print surface of a Prusa MK3S or Ender 3. An update was made with a slightly smaller dial that can be printed on a Prusa Mini or any printer with at least 180x180mm bed size. Both size dials are provided with traditional Roman numerals or simple numbers.

The design is posted to MyMiniFactory

Assembly videos are coming soon.


The clock is provided with a traditional Roman numeral dial and simple numbers. Both styles are provided in a full size and a smaller size that can be printed on a Prusa Mini.



The electronics are taken from a cheap pendulum drive module purchased for under US$4. A minor amount of soldering is needed to extend the battery terminals to span a second AA battery.

The base was designed specifically to fit the electronics shown below. It is one of the cheapest pendulum drivers available on eBay or AliExpress. Unfortunately, it is not readily available on Amazon. The best option appears to be ordering from China and waiting a few weeks for it to arrive.



Here is the view of the back of the clock



This is a close-up view of the pawls used to advance the ratchet. The active pawl on the pendulum arm has many different attach positions to adjust for different pendulum amplitudes. The large round knob on the left is used for setting the time.