There are two common power sources for mechanical clocks -- a spring, or a weight.
This idea is for a clock whose own weight provides the driving force for the mechanism.
A chain would be attached to the top of the clock, go up to the ceiling, over a pulley, and back down to the clock.
The chain
would then make a loop around a sprocket, then come out the bottom of the clock.
It would descend, go around a second pulley (which would be anchored to the floor), then back up to an anchor point on the bottom of the clock.
To power up the clock, one lifts the clock upward; the sprocket around which the chain is wound spins backwards freely by means of a one-way clutch.
To keep the clock from swinging around excessively, it would have either a pair of balance wheels or a pair of pendulums. These would swing 180 degrees out of phase from one another, preventing excessive transfer of momentum to the clock.