Page 288 - Concise Encyclopedia of Robotics

Robot Leg
The main problem
If robots are used in space travel,with the intention of having the machines
replace astronauts, then the distance between the robot and its operator
cannot be very great. The reason is that the control signals cannot travel
faster than 299,792 km/s (186,282 mi/s), the speed of light in free space.
The Moon is approximately 400,000 km, or 1.3 light-seconds, from
Earth. If a robot, not Neil Armstrong, had stepped onto the Moon on that
summer day in 1969, its operator would have had to deal with a delay of
2.6 s between command and response. It would take each command 1.3
s to get to the Moon, and each response 1.3 s to get back to Earth. True
telepresence is impossible with a delay like that. Experts say that the
maximum delay for true telepresence is 0.1 s. The distance between the
robot and its controller thus cannot be more than 0.5, or 1/20, of a light-
second. That is about 15,000 km or 9300 mi—slightly more than the
diameter of Earth.
A possible scenario
Suppose that astronauts are in orbit around a planet whose environment is
too hostile to allow an in-person visit. Then a robot can be sent down. An
example of such a planet is Venus, whose crushing surface pressures would
kill an astronaut in any pressure suit possible with current technology. It
would be easy to sustain an orbit of less than 9300 mi above Venus,however,
so telepresence would be feasible. The operator could sit in a spacecraft in
orbit above the planet, and get the feeling of walking around on the surface.
See also TELEOPERATION and TELEPRESENCE.
ROBOT LEG
A robot leg is an appendage similar to a robot arm,but intended to support
and propel a mobile robot rather than manipulate objects. Legged locomo-
tion has advantages when the terrain in a robot’s world space is irregular
or rough. Legs can also allow robots to jump, sit down, and kick objects.
However,wheel or track drives are usually preferable in work environments
with smooth, comparatively level surfaces.
Humans have dreamed of building machines in their own image. In
reality, humanoid robots almost always are built for amusement. When
robots have legs, stability is a concern. A robot can fall over if it must
stand on one or two legs, or if all its legs are lined up.
Legged robots usually have four or six legs. The legs can be independ-
ently maneuverable, or they can move in groups. Robots with more than
six legs have not often been conceived.
See also BIPED ROBOT, INSECT ROBOT, QUADRUPED ROBOT, TRACK-DRIVE LOCOMOTION,
TRI-STAR WHEEL LOCOMOTION, and WHEEL-DRIVE LOCOMOTION.

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