Pedals 2 and 3 turn about fixed axis A and, through tie-rods 5 and 6, transmit motion to crank 1 which rotates about fixed axis B. Crank 1 is connected by turning pair C to link 7 which is hinged to flat spring 4, secured at point D. Crank 1 is driven by alternately depressing pedals 2 and 3. Spring 4 provides force to enable the mechanism to pass through its extreme positions (dead points).
$614$LW,ML$