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Mechanics for Robot Hands and Arms
— as a proud mercenary — preferred telling everyone that
the accident occurred during an act of war rather than a
barnyard fight.
Götz was born of noble background but quickly made
enemies of any nobleman or person of authority with his
nasty attitude. He began his career at the tender age of 17
as a soldier in the service of Margrave Frederick I in 1497
Germany. He then fought for the Emperor Maximillian I of
the Holy Roman Empire for a few years after that. At the
age of 20, he formed a mercenary troupe and sold his
services to various royal noblemen who needed ruthless
soldiers to attack their enemies. When not ‘employed’ by
these men, he would conduct raids to plunder the wealthy,
much like the mythical Robin Hood of England, but was a
bit more vicious.
A recent article in Wired Magazine highlighted this
amazing mechanical marvel of 500 years ago in an article
entitled Götz of the Iron Hand. It made me realize just how
important the need for a functional hand and arm might be
to a soldier. Just this January, I discussed various types of
robot hands, but these were mostly electrically-driven
specifically for robots. There has been much progress in
prosthetic hands and arms the past few years, and certainly
in the past 500 years.
The actual hand of Götz still exists and is on display
in a German museum. Götz is not only remembered to
this day in Germany for the hand made for him by armor
craftsmen, but for a particularly nasty phrase he often
used that got him imprisoned on several occasions. This
invention is often credited as the foundation of the
modern prosthetics industry. The hand was fashioned
with individual articulated fingers with individual springs
to return them to their extended lengths. An array of
levers and buttons allowed him to grasp a sword or hold a
lance, hold onto the reins of his horse, write with a pen,
and even play cards. He made many enemies during his
long lifetime of mayhem, but managed to
die peacefully in his bed in 1562 at the age
of 82.
to finish the robots in several weeks, and I needed to hire
several friends to build the robot props in my garage while I
was at work at Rockwell. I couldn’t take the time that I
originally wanted to build them myself.
I used an arm configuration from an earlier
promotional robot design of mine that allowed both the
shoulder joint and elbow joint to move together in a natural
human-like motion, without adding an extra motor. Figure
3 shows the earlier promo configuration using a figure 8
cable arrangement and pulley system mounted on a fixed
transverse tubing shaft. The top pulleys are attached to this
shaft and do not rotate; only the upper arm shoulder joint
rotates around the shaft.
When the upper arm/shoulder joint is moved upward
by the shoulder motor — say 45º — the cable tugs at the
bottom elbow pulley, also pulling it upward 45º. This
resulted in a natural arm swing, much like how a human
would move their arm. When the upper arm is straight
down, so is the lower arm. In like fashion, when the
shoulder drives the upper arm segment 90º, the lower arm
segment is driven further 90º so the hand/claw faces
straight up. This allows the robot to not have such a stiff
robotic appearance.
Smooth arm motion is accomplished without the use of
another heavy motor that would weigh down the arm. Part
of the right shoulder linear actuator is barely shown in the
bellows to the left, though a chain drive linked to a motor
in the lower chest cavity was used in the final promo robot
configuration. Figure 4 shows the completed Revenge of
the Nerds robot action prop using a flatter arm/pulley
configuration. This robot used a direct drive to a gearmotor.
Robot Arm Counterbalancing
Another strictly mechanical feature that I’ve used on
several large robots is the use of a coil spring (both
Revenge of the Nerds
Robot Action Prop
Back in late 1983, I was approached by
20th Century Fox prop people about building
a robot action prop (actually four) for a
movie Fox was making called Revenge of the
Nerds. They wanted a ‘robot’ that looked like
a kit that a college freshmen nerd might
build and it had to have two working arms
with claws to hold things. Unfortunately,
after they agreed to my designs and initial
costs, they managed to wait until well into
January to give me the final go-ahead. At
that time, they literally threw money at me
FIGURE 3. A 'figure 8' cable arrangement for
elbow movement.
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