Emily Whiting – TRANSCRIPT
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. 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, 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 archaeological 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. 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.