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WALKING GAITS FOR LEGGED ROBOTS 327

Walking Gaits for Legged Robots

Gait refers to the pattern of leg movement as an animal or insect walks. Gaits can and do
differ depending on the speed of travel— a running gait is wholly different from a walking gait.
The leg motions are distinctive in each one. So, too, for robots, though almost all are restricted
to walking gaits. There aren’t too many legged robots that can run, at least not without falling
over and making fools of themselves.
Figure 27- 8 shows most common gait of a six- legged robot that has independent control
of each leg. This gait is often referred to as an “alternating tripod gait,” because at least three
legs are always touching the ground at the same time, providing static balance. (A similar gait,
also an alternating tripod, is used when the robot uses legs that are linked together. This gait
is described in more detail in “Build a 3- Servo Hexapod,” next.)
The alternating tripod gait goes through a number of sequences, as shown in Figure 27- 8.
For each side of the tripod, the legs are lifted, lowered, and swept forward or backward in
unison. This provides for a reasonably fast walk while still maintaining good static balance as
the weight of the robot is shifted from one side to the other.
The legs act either to lift or to power.

• Legs are lifted to orient them into a new position. During lift, the leg does not provide
propulsion, nor does it contribute to the balance of the robot.
• Legs that power propel the robot in the opposite direction of the movement.
To be sure, there are other gaits for six- legged creatures, living or robotic. They include
metachronal (or wave) and ripple. Space forbids me from detailing each one of these, but you
can learn more about these and others with a Web search.

Figure 27- 8 The alternating tripod gait
common in hexapod robots. Three legs
always touch the ground in a tripod
arrangement. The robot moves by
alternating the side of the triangle that’s on
the ground and “sweeping” those legs in
the opposite direction of intended travel.

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