This is a project I have been working on intermittently for several years. The construction of a working clock requires solving some interesting mechanical problems, including powering the movement, designing an escapement, regulating the movement and constructing a clock face with hands that move on the same axis and at a ration of 1:60.
Powering the movement
Every mechanical Lego clock I have seen so far has used weight to power the movement. A weight is attached to a rotating axle by a thread and hung below the clock – like the weights on a cuckoo clock. Gravity pulls the weight, turning the axle, which drives the movement.
There are a couple things I don’t like about using weight. First, I want to use only Lego parts in my clock. Lego has made some weighted pieces that were used for ballast in a ship model, but I don’t own any. Second, a weight-driven clock needs plenty of room below it to allow for the weight to hang. This means hanging the clock on a wall or placing it at the edge of a table and letting the weight hang toward the floor. This seemed like an inconvenient design requirement.
For these reasons, I decided early on to find a way to drive the movement using a pull back motor. These were included in several car and motorcycle sets, and have a fairly powerful spring inside that can be wound and released. Using a pull back motor would allow me to make a “portable” clock that could be placed on any flat surface.
Designing an Escapement
After experimenting with several types of escapement, I settled on a fairly simple one that uses two old-style 15-tooth gears meshed 90 degrees out of phase, with 4 friction pins in each one. These pins strike the end of a pendulum, which regulates the movement.
Here is a video of the escapement and pendulum I have devised so far. It runs for about 15 minutes on one winding:
I doubled up the pull-back motors and geared them down in an attempt to increase the running time of the clockwork. This just about doubled it from 15 minutes to just over 28 minutes.
I also lengthened the pendulum and made it heavier to increase the period. More tinkering with the pendulum and gearing is in store.
This photo is of the “rough draft” mode. I’ll clean it up with more compact spacing once I hit on the best design.
After trying several configurations, I found a fairly compact way to make the 60:1 gear reduction needed between the second and minute hands. I opted to have the clock hands show seconds and minutes rather than minutes and hours to reduce the number of gears needed.
The clock face is an old-style LEGO gear. These have a wide hole in the center that allow for an axle to pass through and turn freely. The second hand axle runs through the center of the gear, while the minute hand is marked on the face of the gear itself. The two old-style white gears drive the red gear at the proper rate, indicating minutes.
By accident, it turned out that the escapement I designed ran very close to 60 “tick-tocks” per minute. It was just a little faster. Adding the additional work of turning the clockwork slowed it down very close to the proper rate, and the fine tuning was done by weighting and lengthening the pendulum. Here’s a short video of the completed clock running.