Some of the questions we might ask concerning the design of a robot leg are:

• how many leg segments are necessary?

• what about the foot?

• how many DOF's are needed for successful turning?

• what about the head?

• Should the legs be designed as mirror-images front-back? Afterall, Tekken and Collie from Kimura Labs are not designed this way. The Tekken legs all have elbows and no knees, and the Collie legs all have knees and no elbows, but they both walk ok. Collie does look more facile, however.

Some of the potential lessons for robot leg design gleaned from the study of mammals are as follows:

• Front and rear legs should be mirror-images of each other, in order to give stability during all phases of movement - rising, standing, walking, running. This helps keep the COG of the body always centered with respect to the legs and the animal on an even keel during movements.

• The horse obtains its speed and power partly by having relatively short upper leg segments, with the muscle mass located close to the torso, and long lower legs with little mass, thus improving angular acceleration of the legs.

• The leg attachments should be high on the torso in order to prevent the frame from being top heavy.

• The elongation of the lower limbs of horses increases stride and speed, but creates a leverage problem when rising.

• Some sort of compliance mechanism should be built into the legs and feet to absorb the forces of impact at the end of each step.

• For optimal power in the step, some mechanism might be built in for propelling the foot-toe arrangement forward at the start of each suspension, but this is probably less important than heel-leg compliance.

• The Walk and the Trot are quite similar, regards use of diagonals for dynamic stability and sequence of leg movements. The Trot would appear to be the easiest of the rapid gaits to implement on a 4-legged robot. Start the Walk, then lift the suspended legs higher and extend them further and faster, lean the body further forward, and jigger the front-back timing relationships a bit.

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