Dynamics of Nature - Automatic Blocking Mechanism

In any mechanical process when heavy weights are involved, it is important that the lifting wheel does not spin out of control if something goes wrong.
Leonardo studied several variations on a locking system, which blocks the wheel's rotation in the wrong direction while the weight is being lifted. The catch presses against a cog on the wheel, preventing it from spinning backwards and dropping the weight.
The idea, originally used when loading catapults, forms the basis for ratchet- locking mechanisms in use today.