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The GE walking truck was
the first legged machine

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that could move
its legs separately

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to place the feet
on good footholds.

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A human driver controlled
the machines four legs

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by moving his own arms and legs.

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Forced feedback
let the driver feel

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interactions between
each leg and the terrain.

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The GE walking
truck demonstrated

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the technical feasibility
of legged vehicles.

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However, it required a
driver with great skill.

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Computers were
introduced in 1977

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to simplify the driver's task.

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This hexapod built
in the Soviet Union

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was controlled with a mixture
of digital and analog computers.

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Analog computers controlled
the motions of each leg

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while the digital
computer coordinated

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the legs to produce a gait.

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This hexapod, also
operational in 1977,

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relied solely on digital
computers for control.

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In 1982, cameras
and four sensors

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helped it to negotiate
uneven terrain.

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Hirose and Umetani designed
mechanical linkages

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to simplify control
of this quadruped.

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Each leg is a
three-dimensional pantograph

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that transforms linear actuator
motion into linear foot motion.

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Sensors in the feet detect
lateral contact and load

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and a pendulum in the body
measures the vertical.

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The machine climbs uneven stairs
without human intervention.

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The first machines
to balance were

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carts that travel back and
forth to control the tipping

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of an inverted pendulum.

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Cannon's group at
Stanford demonstrated

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balance of a single
inverted pendulum,

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a double inverted pendulum, and
a flexible inverted pendulum.

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Miura and Shimoyama built
the first walking machines

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that balanced.

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The bipeds shown here can tip
fore and aft and sideways,

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but the control computer
positions the feet on each step

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to control the tipping.

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Matsouka built the
first running machine.

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It moved in a plane by
rolling on an incline table.

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An electric motor actuated
the hip and a solenoid

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in the leg delivered thrust
to make the machine hop.

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The goal of our work
in the leg laboratory

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has been to explore
balance in leg locomotion

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with particular attention to the
dynamic aspects of the problem.

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The first machine we
studied had just one leg

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on which it hopped.

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This one-legged
machine permitted

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us to concentrate on
balance while avoiding

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the difficult task of
coordinating many legs.

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A tether mechanism
constraining the machine

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mechanically so it could only
move vertically fore and aft

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and rotate about its pitch axis.

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Other motions were eliminated.

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Compressed air powered the
hopping and sweeping motions

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of the leg and air spring
made the legs springy

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so the hopping
motion of the machine

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was primarily a
passive oscillation.

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Sensors measured leg length,
hip angle, body pitch angle,

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forward running speed,
ground contacts,

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and pneumatic
pressure in the leg.

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The driver used a joystick
to specify the desired

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rate and direction of travel.

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Maximum running speed was
about 2 and 1/2 miles an hour.

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The control system
for this machine

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was simplified by breaking
it down into three parts.

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One part of the control
system excited and regulated

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the vertical bouncing motion.

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The second part controlled
the forward running speed

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by choosing a forward
position for the foot

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during each flight phase.

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The third part of
the control system

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adjusted the posture
of the body by exerting

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a torque between
the leg and the body

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while the foot
touched the floor.

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These three parts of
the control system

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were each synchronized to the
machine's hopping oscillation.

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The operator pressed
the leap button

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to initiate a modified hopping
cycle on the next step.

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To increase clearance
of the foot,

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the control system
delivered maximum leg thrust

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then retracted the leg and
delayed its sweeping motion.

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The three-dimensional
hopping machine

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was similar to
the planar hopper,

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but it had an extra degree
of freedom at the hip.

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The hopping motion was
powered by compressed air

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while the hip was
actuated with hydraulics.

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A pair of gyroscopes measured
the body's pitch, roll,

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and yaw orientations.

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The joystick specified the
desired direction and rate

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of travel given in
laboratory coordinates.

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Top running speed was about
4 and 1/2 miles per hour.

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Once again, the
control was broken down

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into three parts that
regulated hopping

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height, forward running
velocity, and body posture.

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The planar control
system was generalized

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to control the three-dimensional
machine with very little

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conceptual complication.

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In computer simulations, the
three-dimensional hopping

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machine traversed a
variety of simple paths.

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Here, Michael Chaponis drives
the machine along the outside

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of a 1 and 1/2 meter square.

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In this experiment, absolute
position information

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was provided by a sensor mounted
on the laboratory ceiling.

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Each time the driver pressed the
button to advance the machine,

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the control system moved it
from one corner of the path

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to the next.

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Because a biped uses only one
leg for support at a time,

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it can use the one-legged
control algorithms

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for each leg.

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This biped ran using
the same three part

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control that was developed
for the hopping machines.

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However, it required
an additional mechanism

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to sequence the
legs and to retract

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the leg that wasn't being used.

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This is a transition
from a two-legged running

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gait to a hopping gait.

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When hopping, the idle
leg was used like a tail

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to swing out of phase
with the support leg,

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thereby reducing the
pitching motion of the body.

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Top recorded running
speed, shown here,

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was 9 and 1/2 miles per hour.

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This quadruped runs
with a trotting gait.

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It is used to study leg
coordination in the context

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of machines that balance.

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The control system
coordinates pairs of legs

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to work together so they act
like a single equivalent leg.

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With this coordination
in effect,

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quadruped trotting is
equivalent to biped

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running so the biped control
algorithms can be used.

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Once again, control
was broken down

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into three parts that
regulated hopping

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height, forward running
velocity, and body posture.

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In addition to
trotting, this method

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can, in principle,
be used to control

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other gaits that use the
legs in pairs, such as pacing

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and bounding.

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