Check out this amazing wood clock contraption by Steve K. It is a weight driven clock with a very novel way of bringing the weight into play.
From the video description:
This wood gear mantel clock uses steel balls retained in holes in the hour gear to provide the clock drive torque. There are 15 holes and 7 steel balls. Every 4 minutes the lowest ball is ejected from the gear and runs down a track to a lift mechanism that elevates the ball to another track where it is guided into an empty hole in the gear. The lift mechanism is driven by a 3 rpm timing motor hidden in the base.
The clock uses what is known as aGraham escapement coupled to a dumbbell pendulum. The creator says it varies a couple of minutes per day, but doesn't mind because of the ball mechanism. I would feel the same way!
[ Thanks Christoph! ]