Patent ID: 8328216

Claim:
A retractable/extendable crank comprising: a fixed arm having an end coupled to a rotary shaft of a rotary body to transmit torque and a cam guide on a side wall of the fixed arm engaged with a guide groove or a guide protrusion of a cylindrical cam; a movable arm retracting and extending while longitudinally sliding in the fixed arm; the cylindrical cam disposed in the movable arm in an axial direction of the movable arm and having the guide groove or the guide protrusion engaging with the cam guide of the fixed arm; a pedal composed of a pedal shaft coupled to an exposed end of the movable arm and a pedal plate coupled to the pedal shaft, the pedal plate not rotating with the pedal shaft; and a pair of bevel gears coupled to a camshaft of the cylindrical cam and the pedal shaft of the pedal, respectively, and having a tooth ratio of 1:1.