For some weird reason I thought of the inverse of the thermodynamic drinking bird toy instead of using a closed system with thermally sensitive fluid where the bird dips it's beak which causes the movement to continue
except here the design is so simple that once the weight of the water overcomes the weight of the hammer on the other end of the fulcrum it tips spilling the water.
Genius really when you consider as Marv pointed out the low friction and almost complete lack of any possibility of stiction until the pivot wore down