I decided to try and build another model using my LEGO escapement mechanism, and came up with this model of two kids playing on a seesaw (or a teeter-totter, as it is often called).
There are a couple of differences to note between this model and the model of the cow jumping over the moon. For example, in this model the seesaw itself acts as the pendulum. I have also introduced a 3 to 1 gear reduction between the escapement gear and the spool letting out the weight. This results in a run time that is 3 times longer than it normally would be (15 minutes for this model), but also requires that the weight be 3 times the mass in order to exert the same forces on the escapement arms. Of course, this could be expanded even more, with further gear reductions or the introduction of pulleys, to produce even longer run times.
I have put together building instructions for the core escapement mechanism, if you would like to see how it is built, or even try to incorporate it in your own models.
Note that the performance depends heavily on how freely the pendulum can swing and the escapement gear can turn. Try your best to align all the Technic components to minimize any friction in the system.