11.11  Ratchets, freewheels and indexing

Mechanisms that move in one direction only or in steps. The ratchet and pawl: the tooth angle that keeps the pawl engaged under load, by the friction condition of Friction. Freewheels with rollers and sprags, as in the rear hub of a bicycle, and the wedging angle that decides whether they lock or slip. The Geneva drive, its indexing time ratio and the acceleration at entry and exit. The escapement of a clock, which releases a stored energy one step at a time. Example: a printed ratchet for a winch, its pawl force and the tooth that fails first.