Understanding Legged Locomotion: Gaits, Phases, and Cycles, Slides of Computer Graphics and Animation

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Locomotion

Legged Locomotion

Gaits

 A gait refers to a particular sequence of lifting

and placing the feet during legged locomotion

(gallop, trot, walk, run…)

 Each repetition of the sequence is called a gait

cycle

 The time taken in one complete cycle is the gait

period

 The inverse of the period is the gait frequency

(1/period)

 Normally, in one gait cycle, each leg goes

through exactly one complete step cycle

Gait Phase

 We can think of the gait phase a value that

ranges from 0 to 1 as the gait cycle proceeds

 We can choose 0 as being any arbitrary point

within the cycle (such as when the back left foot

begins its step)

 The phase is like a clock that keeps going round

and round (0…1, 0…1, 0…1)

 For a particular gait, the stepping of the legs and

all other motion of the character can be

described relative to the gait phase

Duty Factor

 The relative amount of time a foot spends on the ground is called the duty factor  For a human walking, the duty factor will be greater than 0.5, indicating that there is an overlap time when both feet are on the ground  For a run, the duty factor is less than 0.5, indicating that there is a time when both feet are in the air and the body is undergoing ballistic motion GaitPeriod SupportDur ation DutyFactor =

Step Phase

 The step phase is a value that ranges from 0 to

1 during an individual leg’s step cycle

 We can choose 0 to indicate the moment when

the foot begins to lift (i.e., the beginning of the

transfer phase)

 The foot contacts the ground and comes to rest

when the phase equals 1 minus the duty factor

Locomotion Terminology

 Gait

 Gait cycle  Gait period  Gait frequency  Gait phase

 Stepping

 Step cycle  Step phase  Support stage, support duration  Transfer stage, transfer duration  Duty factor  Step trigger

Gait Description

 A simple description of the timing of a

particular gait requires the following

information

 Number of legs

 Gait period

 Duty factor & step trigger for each leg