March/April 2021 23Gundam Factory Yokohama, the organization that
built the robot, did not return multiple interview
requests for this story.
These U.S.-based roboticists believe that it
would be nothing short of an engineering marvel
for a robot of this size to really walk, run, and wreak
havoc; the laws of physics would be pushed to their
logical extremes. Specifically, scaling rules would
dictate a whole slew of changes to the actuators (or
motors) that allow the Gundam to raise its legs and
take strides.
“By scaling rules, it means that if you make
something bigger, then different aspects of it
get bigger or smaller in different ways,” explains
Andy Ruina, Ph.D., a professor of mechanical engi-
neering at Cornell University’s Sibley School of
Mechanical and Aerospace Engineering.
Scaling rules are not just the stuff of robotics.
Moore’s law predicts that the number of transistors
in a silicone computer chip will double every two
years as the technology advances. Allometry, the
biological study of the scaling relationship between
the size of a body part and the size of the entire
body, describes why ants can haul roughly 100
times their weight and humans can’t, Ruina says.
In the case of a mammoth Gundam, the motors
that allow the hulking robot to move must become
drastically stronger, especially if the frame is made
from a heavy metal, like steel. But if the motors are
larger, they’ll also become heavier and weaker rel-
ative to the torques, or rotational forces, necessary.
In this way, the scaling is “unfortunate,” accord-
ing to Chris Atkeson, Ph.D., a professor at Carnegie
Mellon University’s Robotics Institute.
To get around this paradigm, he says, engineers
could attempt to create a whole new kind of motor.
“The scaling laws assume that technolog y is always
the same...but you can change the technology so
that it works,” Atkeson says.
Electric motors like the ones used in Gundam are
composed of two kinds of magnets to impart motion.
The first is a permanent magnet, which is often
made of naturally occurring materials, like rare
earth metals. These magnets retain their magnetic
properties, even in the absence of an electric current
or an inducing field. Then there are electromagnets,
which rely on coils of wire to act like a magnet when
an electric current passes through.
Motors rely on the interaction between the
permanent magnet and electromagnet to create
mechanical energy. As the electromagnet’s polarity
is manipulated by electricity, it spins, rotating an
axle that can drive the Gundam’s leg, for instance.
If that spinning motion becomes stronger, so
will the motor. To make it happen, an engineer
would introduce a larger magnetic field, Atkeson
explains. Theoretically, he says, you could create
an electromagnet as large as a neutron star—the
collapsed core of a massive supergiant star—but
there are practical limitations on Earth, as there
is a limit to how much an object can be magnetized.
Magnetic resonance imaging machines, or
MRIs, push those boundaries, as some of the stron-
gest man-made magnets. So, if engineers could
create motors with the power of an MRI machine,
they could almost certainly get the colossal Gun-
dam to walk. Of course, new issues arise; namely,
the robot’s mass ends up being dominated by the 24
actuators required to create 24 degrees of freedom.
“An engineering black hole ensues, where no
matter how big the actuators, the robot is still too
weak to move at the desired speed,” Atkeson says.
This is partly why legged robots—and the exact-
ing locomotion that they demand—are difficult
to successfully engineer, even for the world’s top
robotics experts.
So maybe this whale of a Gundam can’t really
walk. It’s still a feat of engineering that it’s stiff
enough to move the way it does without substan-
tial vibration, Atkeson says. And between its sheer
size, illuminated eyes, and ability to wave, it’s the
kind of ambassador that any country would be
proud to have.
Translation: It’s one substantial step forward
for robotkind.Math of Scaling Laws
Basic rules in geometry and physics—
plus the strength restraints of
materials—are one reason it’s
difficult to create robots that can
walk. As linear dimensions increase,
two-dimensional quantities, like how
much “skin” you need to cover the
robot, scale up by a power of two.
Three-dimensional quantities, like
mass, increase by a power of three.Forces due to gravity scale up by a
power of three, and forces due to
acceleration scale up by a power of
four. Torques due to gravity scale
up by a power of four, and torques
due to angular acceleration scale up
by a power of five. Therefore, small
escalations in size lead to slower
movements, and the need for those
massive motors.