HAMMER CLOCK

A clock in which the time period depends on the length of the hammer and the movement is sustained by the action of an electromagnet on the hammer's iron mass.

where T is the time taken for one swing, L is the length of the hammer, and g is a constant - the acceleration of gravity. So T varies only depending on L. For small swings such as this, the amplitude of the swing has no effect on the time period.

The pendulum can be considered as an astable system:

This is an example of an astable piston-style engine: