3D printing — the physics of objects | Emily Whiting | TEDxBeaconStreet

3D printing — the physics of objects | Emily Whiting | TEDxBeaconStreet


Translator: Bob Prottas
Reviewer: Leonardo Silva A few years ago on a trip to China,
I came across this toy. It’s made of bamboo
and it looks like a dragonfly. And this one has a secret. When you put it on the tip of its nose,
it performs this surprising balancing act. It seems to float. What I find fascinating about this toy is that it’s not the way it looks that’s
interesting, but rather what it can do. That when placed in this precise way
it seems to come alive in my hand. Now I’m a computer scientist
and what this means is that I spend most of my time thinking
about ideas and objects that exist only in the virtual world,
behind a computer screen. And around the same time that I found
this toy I was learning about 3D printers. Now 3D printers were a revelation to me
because they gave me this opportunity to take objects out of the virtual world
and into the physical. So I could finally take a digital object,
and by 3D printing it, hold it in my hand. And the question that I asked was: could I also create objects
like this little dragonfly that have a secret ability? So many of you in this room are probably
familiar with 3D printers. They’re an additive manufacturing
technique that allow anyone regardless of your skill level to create
perfectly crafted and complex 3D objects. And now this has had an enormous impact
on the design and manufacturing industry. We’ve seen a explosion of complex forms
in sculpture, fashion design, prosthetics, and even if you do not have a background
in art history or design, there’s a wealth of objects
available online. You can simply go to an online database
and choose a shape and press print. So 3D printing has brought
manufacturing to the masses. But I believe that there’s still something
beyond these complex appearances, that there’s an untapped potential in the
way we design objects for 3D printing. Let me show you the first model
that I tried to print. Here we have a horse downloaded from
an online database. It captures in 3D
this classic dynamic pose that we see in the photograph in 2D. Here’s what happened
when I tried to 3D print it. You can imagine
what is about to transpire. So this highlights a problem. In the digital realm,
where this horse initially existed, we don’t know how it’s going to behave
or how much it weighs, or if it’s going to stand or not. But as long as it looks plausible
perhaps that’s all that matters. But in the physical world
there is no cheating. We have to get that physics right and I argue that getting the physics right
is not just a constraint, but it can be a powerful tool that we can
use physics to create objects of fun and beauty
in the way that we design. So I used this horse as a challenge. With researchers
from ETH Zürich and INRIA, we devised a way to use the capabilities
of fabrication to make that horse stand. So what is it that makes an object stable? Here we have an armadillo man
practicing yoga, but he’s not getting
his tree pose quite right. In reality he would fall over and we can determine this by looking
at something called the center of mass. There’s a single 3D point
that represents the full weight and positioning of his entire body and if that 3D point
falls outside of the region where he contacts the ground, he’ll fall. We developed a computational method that
would change the design of these objects to suit this stability test. We changed the design in 2 ways. First by taking material out
of the interior of the shape. So by hollowing out this region in yellow
we shift his balance over to the left. This gets us most of the way there
but he’s not quite stable yet, and so a second step is to deform his body
pushing his posture over to the left and these 2 steps together
stabilize his stance and when brought into reality
via 3D printing, his tree pose now stands. (Applause) So this process of hollowing
and deforming together can also be applied to multiple poses. For example, you can design a teddy bear
so that he can balance in 2 different break dancing stances, (Laughter) and I have printed this model
in transparent material so you can see the complexity
of the final result. That there’s this precisely shaped
interior volume, and this is where 3D printing
becomes essential. To craft
such an intricate internal structure would be basically impossible to do
with traditional tools. So 3D printing provides us with that
precision we require for this T-rex to stand
on his tiny T-rex feet, and the horse can stand
almost impossibly on his hind legs. So static balance is an elegant example
of how we can use physics to create objects of fascination. But there’s more to it.
We can also look at motion, for example. It turns out we can use similar
computational tools for dynamic behavior. So an example that we’re probably
all familiar with from a young age is spinning tops. Spinning tops achieve a state of balance
that’s only possible while in motion. Surprisingly spinning tops are among
the oldest known toys in human civilization. Here we have an artifact
from an archeological dig. This is from ancient Greece
dated to 480 BC. We see 2 characters spinning a top
on the ground transfixed by its motion. But the design of these toys
hasn’t changed since the time of the ancient Greeks
in all those thousands of years. Today’s tops look the same
as what we see in this painting, and the reason
is a limitation in technology. So what is the challenge
in making a spinning top? Here we have a teapot that’s pretty close
to being rotationally symmetric. Yet simply adding a spike its bottom
and giving it a twirl doesn’t accomplish very much. There are precise physical principles
that have to be met. So the first is balance. That 3D point, the center of mass, needs
to fall exactly over the contact point, and the second is principle called
the moment of inertia. Every physical object
has a set of directions about which it is able to spin. These directions are determined
by properties of symmetry and how the mass is arranged. The key to a spinning top is that
in order to spin stably about an axis it has to align with this frame. So designing under these principles for a rounded symmetric object
might be intuitive. But when you’re faced
with more irregular asymmetric objects, this problem becomes quite complex. So the goal of an algorithm
that I developed with researchers from ETH Zürich
and Disney research was to redesign these shapes
to let them spin. So similarly to what we saw
with the yoga-performing armadillo man, we can look at the interior structure. We assess individual chunks
on the interior and for each chunk determine whether
it should be hollow or solid and the result is a solid model
where the rotational directions are aligned precisely
with that spinning axis, and through 3D printing
the heart can spin on its arrow. (Applause) The teapot where it once
simply fell over on its side now has this new talent
of spinning like a top. The exterior has not changed. But by precisely tuning
that interior structure, the mass distribution,
it can now spin like a top. An elephant, very far from what
we’d expect as an elegant animal. But with our computational technique
paired with 3D printing, it can now spin on its toe. A far cry from the tops
of the ancient Greeks. What I’ve illustrated for you here today
is how we can use this notion of balance to create objects of fascination, to reimagine the abilities
of everyday objects, by considering not just
the exterior appearance but the physical behavior
of these designs. This is just a glimpse
into what the possibilities are. I started this talk
with this little dragonfly that performs
a surprising feat of balance. If we think about it, so much of the way
that we live and play and interact with the world around us is controlled
and inspired by these properties of motion and balance, and as we progress with 3D printing
to evermore sophisticated materials, higher levels of precision and complexity, we can only imagine
what that future might hold. Think of architecture. Could we 3D print buildings
that rebalance themselves in response to the vibrations
of earthquakes? Could we 3D print clothing for fashion
design that counterbalance the body? The golden ticket is this pairing
between physics and the control that 3D printers give us over the entire
internal structure of our designs. As your mother may have said:
“It’s what’s inside that counts.” Thank you. (Applause)

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