Gait Planning

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Gait PlanningMovements that produce locomotion


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What is Gait?

After designing a leg mechanism itis necessary to perform a leg anda body motion sequence to makethe mechanism move. This

sequence is known as Gait.

It is defined by the time and thelocation of the placing and lifting

of each foot in order to move bodyfrom one place to another.


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Types of Gaits

Statically balanced:

Characterized by a relativelyslower speed locomotion.

Dynamic effects become negligibleduring the locomotion

Dynamically balanced:

Characterized by a fast speedlocomotion

Dynamic effects are significant

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CLASSIFICATION

Gaits

Staticallybalanced

Repetition based

Periodic

Wave gait

Equal phase gait

Non-

periodic

Terrain

based

Level

walking

Gaits onperfectly

smoothterrain

Longitudinal walking

Crab walking

Turning motion

Forbiddenareas terrain

Follow the leader

Free adaptiveObstaclewalking

Dynamically

balanced

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Wave Gait

In the Wave Gait, front pair of legsare moved forward, followed bythe middle and then the rear one.

Since only 2 legs are lifted at atime, with the other 4 being down,the robot is always in a highly-stable posture.

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Diagrammatic view of Wave Gait

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Tripod Gait

A tripod consists of the front-backlegs on one side and the middleleg on the opposite side. For eachtripod, the legs are lifted, lowered,

and moved forwards andbackwards in unison

the weight is simply shiftedalternately from one tripod to the

other

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Diagrammatic view of Tripod Gait

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Straight- Forward Walking Gate

Straight Forward or Longitudinalwalking Gait has zero body rotation indirection identical to that of thelongitudinal axis of the trunk body of

the robot

The angle between the direction ofmotion and the longitudinal axis of therobot body is zero

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Crab Walking Gait

Walking in the direction other thanthe longitudinal axis with zerobody rotation

The angle between the direction ofmotion and the longitudinal axis ofthe robot body is known as crabangle

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Turning Motion Gait

Walking motion of a robot about aturning center

During turning the headingdirection of the body changes

Most important for the omni-directional walking of a multi

legged robot

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GAITTERMINOLOGIES

With respect to wave gait of six leggedrobot

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Gait-

it is defined as time and location of placing andlifting of each foot, coordinated with the motion of thebody, in order to move the body from one place toanother.


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Transfer or swing phase-

It is period during which foot is not on the ground.

Support phase-

It is Period during which foot is on the ground.


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Cycle time(T)-

It is time for one complete cycle for leglocomotion of periodic gait.

Duty factor()-it is time fraction of complete cycle time during

which a particular leg is in support phase.


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Stride()-

It is the distance through which center of gravitytranslates during one complete locomotioncycle.

Leg stroke(Rs)-

Distance through which the foot tip of a leg is

translated relative to trunk body duringsupport phase.


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Periodic gait-

A gait is called periodic if similar states ofsame leg during successive strokes occur atsame interval for all legs, that intervalbeing the cycle time.

otherwise it is a non periodic gait.


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Symmetric gait-

A gait is symmetric if the motion of legs of anyright-left pair is exactly half a cycle out ofphase.

Regular gait-

A regular gait is gait with same duty factor for allthe legs


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It is periodic, regular and symmetric gait, in whichthe sequence of placing events of the legs on eachside runs from the rear leg and proceeds forwardto the front leg.

Lateral offset(Y)-Shortest distance between vertical projection of the

hip on the ground and the corresponding track.

Wave gait-


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Mathematical Relation between terms

Leg transfer Time=ta

support time=ts

Cycle time,T=ta+ts

Duty factor = ts/T.

Velocity v=Rs/ts


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Conclusion

Thus, stroke Rs=v*ta*/(1-).

Leg transfer time decreases with increasing

duty factor.

high duty factor , faster is the rate oftransfer.

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Gait Planning

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