A leg mechanism (walking mechanism) is an assembly of links and joints (a linkage) intended to simulate the walking motion of humans or animals. Mechanical legs can have one or more actuators, and can perform simple planar or complex motion.

Compared to a wheel, a leg mechanism is potentially better fitted to uneven terrain, as it can step over obstacles.^[1]

Design goals

• horizontal speed as constant as possible while touching the ground (support phase)^[1][2]
• while the foot is not touching the ground, it should move as fast as possible
• constant torque/force input (or at least no extreme spikes/changes)
• stride height (enough for clearance, not too much to conserve energy)
• the foot has to touch the ground for at least half of the cycle for a two/four leg mechanism^[1] or respectively, a third of the cycle for a three/six leg mechanism
• minimized moving mass
• vertical center of mass always inside the base of support^[1]
• the speed of each leg or group of legs should be separately controllable for steering^[2]
• the leg mechanism should allow forward and backward walking^[2]

Another design goal can be, that stride height and length etc. can be controlled by the operator.^[2] This can relatively easily be achieved with a hydraulic leg mechanism, but is not practicable with a crank-based leg mechanism.^[2]

The optimization has to be done for the whole vehicle – ideally the force/torque variation during a rotation should cancel each other out.^[1]

History

Richard Lovell Edgeworth tried in 1770 to construct a machine he called a "Wooden Horse", but was not successful.^[3][4]

The Plantigrade Machine by Pafnuty Chebyshev was shown at the Exposition Universelle (1878).

Gallery

Stationary

• Jansen linkage

• Klann linkage

• Eight-bar leg mechanism ^[5]

• Tokyo Institute of Technology walking chair^[6]

• 2 DOF pantograph leg mechanism^[7]

• 2 DOF leg mechanism of the RPRPR type.^[8]

• Strandbeest (applied Jansen linkage)

• Ghassaei Linkage^[1]

• Tchebyshevs plantigrade machine^[9]

• TrotBot Linkage (without heel linkage)^[10]

• TrotBot without Heel Linkage^[10]

• One Corner of 12-leg TrotBot^[11]

• Strider Linkage - One Corner of 12 Leg Robot^[11]

• Strider Linkage^[12]

• Strider Linkage with Toes^[12]

• Foot-Paths of Strandbeest, TrotBot, Strider and Klann Linkages

Walking

Complex mechanism

Shown above are only planar mechanisms, but there are also more complex mechanism:

See also

• Jansen's linkage
• Kinematics
• Kinematic pairs
• Klann linkage
• Chebyshev's Lambda Mechanism
• Linkage (mechanical)
• Machine
• Mobile robot
• Hexapod (robotics)