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The GE walking truck was the first legged machine
that could move its legs separately
to place the feet on good footholds.
A human driver controlled the machines four legs
by moving his own arms and legs.
Forced feedback let the driver feel
interactions between each leg and the terrain.
The GE walking truck demonstrated
the technical feasibility of legged vehicles.
However, it required a driver with great skill.
Computers were introduced in 1977
to simplify the driver's task.
This hexapod built in the Soviet Union
was controlled with a mixture of digital and analog computers.
Analog computers controlled the motions of each leg
while the digital computer coordinated
the legs to produce a gait.
This hexapod, also operational in 1977,
relied solely on digital computers for control.
In 1982, cameras and four sensors
helped it to negotiate uneven terrain.
Hirose and Umetani designed mechanical linkages
to simplify control of this quadruped.
Each leg is a three-dimensional pantograph
that transforms linear actuator motion into linear foot motion.
Sensors in the feet detect lateral contact and load
and a pendulum in the body measures the vertical.
The machine climbs uneven stairs without human intervention.
The first machines to balance were
carts that travel back and forth to control the tipping
of an inverted pendulum.
Cannon's group at Stanford demonstrated
balance of a single inverted pendulum,
a double inverted pendulum, and a flexible inverted pendulum.
Miura and Shimoyama built the first walking machines
that balanced.
The bipeds shown here can tip fore and aft and sideways,
but the control computer positions the feet on each step
to control the tipping.
Matsouka built the first running machine.
It moved in a plane by rolling on an incline table.
An electric motor actuated the hip and a solenoid
in the leg delivered thrust to make the machine hop.
The goal of our work in the leg laboratory
has been to explore balance in leg locomotion
with particular attention to the dynamic aspects of the problem.
The first machine we studied had just one leg
on which it hopped.
This one-legged machine permitted
us to concentrate on balance while avoiding
the difficult task of coordinating many legs.
A tether mechanism constraining the machine
mechanically so it could only move vertically fore and aft
and rotate about its pitch axis.
Other motions were eliminated.
Compressed air powered the hopping and sweeping motions
of the leg and air spring made the legs springy
so the hopping motion of the machine
was primarily a passive oscillation.
Sensors measured leg length, hip angle, body pitch angle,
forward running speed, ground contacts,
and pneumatic pressure in the leg.
The driver used a joystick to specify the desired
rate and direction of travel.
Maximum running speed was about 2 and 1/2 miles an hour.
The control system for this machine
was simplified by breaking it down into three parts.
One part of the control system excited and regulated
the vertical bouncing motion.
The second part controlled the forward running speed
by choosing a forward position for the foot
during each flight phase.
The third part of the control system
adjusted the posture of the body by exerting
a torque between the leg and the body
while the foot touched the floor.
These three parts of the control system
were each synchronized to the machine's hopping oscillation.
The operator pressed the leap button
to initiate a modified hopping cycle on the next step.
To increase clearance of the foot,
the control system delivered maximum leg thrust
then retracted the leg and delayed its sweeping motion.
The three-dimensional hopping machine
was similar to the planar hopper,
but it had an extra degree of freedom at the hip.
The hopping motion was powered by compressed air
while the hip was actuated with hydraulics.
A pair of gyroscopes measured the body's pitch, roll,
and yaw orientations.
The joystick specified the desired direction and rate
of travel given in laboratory coordinates.
Top running speed was about 4 and 1/2 miles per hour.
Once again, the control was broken down
into three parts that regulated hopping
height, forward running velocity, and body posture.
The planar control system was generalized
to control the three-dimensional machine with very little
conceptual complication.
In computer simulations, the three-dimensional hopping
machine traversed a variety of simple paths.
Here, Michael Chaponis drives the machine along the outside
of a 1 and 1/2 meter square.
In this experiment, absolute position information
was provided by a sensor mounted on the laboratory ceiling.
Each time the driver pressed the button to advance the machine,
the control system moved it from one corner of the path
to the next.
Because a biped uses only one leg for support at a time,
it can use the one-legged control algorithms
for each leg.
This biped ran using the same three part
control that was developed for the hopping machines.
However, it required an additional mechanism
to sequence the legs and to retract
the leg that wasn't being used.
This is a transition from a two-legged running
gait to a hopping gait.
When hopping, the idle leg was used like a tail
to swing out of phase with the support leg,
thereby reducing the pitching motion of the body.
Top recorded running speed, shown here,
was 9 and 1/2 miles per hour.
This quadruped runs with a trotting gait.
It is used to study leg coordination in the context
of machines that balance.
The control system coordinates pairs of legs
to work together so they act like a single equivalent leg.
With this coordination in effect,
quadruped trotting is equivalent to biped
running so the biped control algorithms can be used.
Once again, control was broken down
into three parts that regulated hopping
height, forward running velocity, and body posture.
In addition to trotting, this method
can, in principle, be used to control
other gaits that use the legs in pairs, such as pacing
and bounding.
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