It’s hard to think of a more dramatic way to make an entrance than falling from the sky. While it certainly happens often enough on the silver screen, whether or not it can be done in real life is a tantalizing challenge for our entertainment robotics team at Disney Research.

Falling is tricky for two reasons. The first and most obvious is what Douglas Adams referred to as “the sudden stop at the end.” Every second of free fall means another 9.8 m/s of velocity, and that can quickly add up to an extremely difficult energy dissipation problem. The other tricky thing about falling, especially for terrestrial animals like us, is that our normal methods for controlling our orientation disappear. We are used to relying on contact forces between our body and the environment to control which way we’re pointing. In the air, there’s nothing to push on except the air itself!

Finding a solution to these problems is a big, open-ended challenge. In the clip below, you can see one approach we’ve taken to start chipping away at it.

The video shows a small, stick-like robot with an array of four ducted fans attached to its top. The robot has a piston-like foot that absorbs the impact of a small fall, and then the ducted fans keep the robot standing by counteracting any tilting motion using aerodynamic thrust.

Raphael Pilon [left] and Marcela de los Rios evaluate the performance of the monopod balancing robot.Disney Research

The standing portion demonstrates that pushing on the air isn’t only useful during freefall. Conventional walking and hopping robots depend on ground contact forces to maintain the required orientation. These forces can ramp up quickly because of the stiffness of the system, necessitating high bandwidth control strategies. Aerodynamic forces are relatively soft, but even so, they were sufficient to keep our robots standing. And since these forces can also be applied during the flight phase of running or hopping, this approach might lead to robots that run before they walk. The thing that defines a running gait is the existence of a “flight phase” - a time when none of the feet are in contact with the ground. A running robot with aerodynamic control authority could potentially use a gait with a long flight phase. This would shift the burden of the control effort to mid-flight, simplifying the leg design and possibly making rapid bipedal motion more tractable than a moderate pace.

Richard Landon uses a test rig to evaluate the thrust profile of a ducted fan.Disney Research

In the next video, a slightly larger robot tackles a much more dramatic fall, from 65’ in the air. This simple machine has two piston-like feet and a similar array of ducted fans on top. The fans not only stabilize the robot upon landing, they also help keep it oriented properly as it falls. Inside each foot is a plug of single-use compressible foam. Crushing the foam on impact provides a nice, constant force profile, which maximizes the amount of energy dissipated per inch of contraction.

In the case of this little robot, the mechanical energy dissipation in the pistons is less than the total energy needed to be dissipated from the fall, so the rest of the mechanism takes a pretty hard hit. The size of the robot is an advantage in this case, because scaling laws mean that the strength-to-weight ratio is in its favor.

The strength of a component is a function of its cross-sectional area, while the weight of a component is a function of its volume. Area is proportional to length squared, while volume is proportional to length cubed. This means that as an object gets smaller, its weight becomes relatively small. This is why a toddler can be half the height of an adult but only a fraction of that adult’s weight, and why ants and spiders can run around on long, spindly legs. Our tiny robots take advantage of this, but we can’t stop there if we want to represent some of our bigger characters.

Louis Lambie and Michael Lynch assemble an early ducted fan test platform. The platform was mounted on guidewires and was used for lifting capacity tests.Disney Research

In most aerial robotics applications, control is provided by a system that is capable of supporting the entire weight of the robot. In our case, being able to hover isn’t a necessity. The clip below shows an investigation into how much thrust is needed to control the orientation of a fairly large, heavy robot. The robot is supported on a gimbal, allowing it to spin freely. At the extremities are mounted arrays of ducted fans. The fans don’t have enough force to keep the frame in the air, but they do have a lot of control authority over the orientation.

Complicated robots are less likely to survive unscathed when subjected to the extremely high accelerations of a direct ground impact, as you can see in this early test that didn’t quite go according to plan.

In this last video, we use a combination of the previous techniques and add one more capability – a dramatic mid-air stop. Ducted fans are part of this solution, but the high-speed deceleration is principally accomplished by a large water rocket. Then the mechanical legs only have to handle the last ten feet of dropping acceleration.

Whether it’s using water or rocket fuel, the principle underlying a rocket is the same – mass is ejected from the rocket at high speed, producing a reaction force in the opposite direction via Newton’s third law. The higher the flow rate and the denser the fluid, the more force is produced. To get a high flow rate and a quick response time, we needed a wide nozzle that went from closed to open cleanly in a matter of milliseconds. We designed a system using a piece of copper foil and a custom punch mechanism that accomplished just that.

Grant Imahara pressurizes a test tank to evaluate an early valve prototype [left]. The water rocket in action - note the laminar, two-inch-wide flow as it passes through the specially designed nozzleDisney Research

Once the water rocket has brought the robot to a mid-air stop, the ducted fans are able to hold it in a stable hover about ten feet above the deck. When they cut out, the robot falls again and the legs absorb the impact. In the video, the robot has a couple of loose tethers attached as a testing precaution, but they don’t provide any support, power, or guidance.

“It might not be so obvious as to what this can be directly used for today, but these rough proof-of-concept experiments show that we might be able to work within real-world physics to do the high falls our characters do on the big screen, and someday actually stick the landing,” explains Tony Dohi, the project lead.

There are still a large number of problems for future projects to address. Most characters have legs that bend on hinges rather than compress like pistons, and don’t wear a belt made of ducted fans. Beyond issues of packaging and form, making sure that the robot lands exactly where it intends to land has interesting implications for perception and control. Regardless, we think we can confirm that this kind of entrance has–if you’ll excuse the pun–quite the impact.

This is a guest post. The views expressed here are solely those of the author and do not represent positions of IEEE Spectrum or the IEEE.

If Disney’s history of storytelling has taught us anything, it’s to never underestimate the power of a great sidekick. Even though sidekicks aren’t the stars of the show, they provide life and energy and move the story along in important ways. It’s hard to imagine Aladdin without the Genie, or Peter Pan without Tinker Bell.

In robotics, however, solo acts proliferate. Even when multiple robots are used, they usually act in parallel. One key reason for this is that most robots are designed in ways that make direct collaboration with other robots difficult. Stiff, strong robots are more repeatable and easier to control, but those designs have very little forgiveness for the imperfections and mismatches that are inherent in coming into contact with another robot.

Having robots work together–especially if they have complementary skill sets–can open up some exciting opportunities, especially in the entertainment robotics space. At Walt Disney Imagineering, our research and development teams have been working on this idea of collaboration between robots, and we were able to show off the result of one such collaboration in Shanghai this week, when a little furry character interrupted the opening moments for the first-ever Zootopia land.

Our newest robotic character, Duke Weaselton, rolled onstage at the Shanghai Disney Resort for the first time last December, pushing a purple kiosk and blasting pop music. As seen in the video below, the audience got a kick out of watching him hop up on top of the kiosk and try to negotiate with the Chairman of Disney Experiences, Josh D’Amaro, for a new job. And of course, some new perks. After a few moments of wheeling and dealing, Duke gets gently escorted offstage by team members Richard Landon and Louis Lambie.

What might not be obvious at first is that the moment you just saw was enabled not by one robot, but by two. Duke Weaselton is the star of the show, but his dynamic motion wouldn’t be possible without the kiosk, which is its own independent, actuated robot. While these two robots are very different, by working together as one system, they’re able to do things that neither could do alone.

The character and the kiosk bring two very different kinds of motion together, and create something more than the sum of their parts in the process. The character is an expressive, bipedal robot with an exaggerated, animated motion style. It looks fantastic, but it’s not optimized for robust, reliable locomotion. The kiosk, meanwhile, is a simple wheeled system that behaves in a highly predictable way. While that’s great for reliability, it means that by itself it’s not likely to surprise you. But when we combine these two robots, we get the best of both worlds. The character robot can bring a zany, unrestrained energy and excitement as it bounces up, over, and alongside the kiosk, while the kiosk itself ensures that both robots reliably get to wherever they are going.

Harout Jarchafjian, Sophie Bowe, Tony Dohi, Bill West, Marcela de los Rios, Bob Michel, and Morgan Pope.Morgan Pope

The collaboration between the two robots is enabled by designing them to be robust and flexible, and with motions that can tolerate a large amount of uncertainty while still delivering a compelling show. This is a direct result from lessons learned from an earlier robot, one that tumbled across the stage at SXSW earlier this year. Our basic insight is that a small, lightweight robot can be surprisingly tough, and that this toughness enables new levels of creative freedom in the design and execution of a show.

This level of robustness also makes collaboration between robots easier. Because the character robot is tough and because there is some flexibility built into its motors and joints, small errors in placement and pose don’t create big problems like they might for a more conventional robot. The character can lean on the motorized kiosk to create the illusion that it is pushing it across the stage. The kiosk then uses a winch to hoist the character onto a platform, where electromagnets help stabilize its feet. Essentially, the kiosk is compensating for the fact that Duke himself can’t climb, and might be a little wobbly without having his feet secured. The overall result is a free-ranging bipedal robot that moves in a way that feels natural and engaging, but that doesn’t require especially complicated controls or highly precise mechanical design. Here’s a behind-the-scenes look at our development of these systems:

Disney Imagineering

To program Duke’s motions, our team uses an animation pipeline that was originally developed for the SXSW demo, where a designer can pose the robot by hand to create new motions. We have since developed an interface which can also take motions from conventional animation software tools. Motions can then be adjusted to adapt to the real physical constraints of the robots, and that information can be sent back to the animation tool. As animations are developed, it’s critical to retain a tight synchronization between the kiosk and the character. The system is designed so that the motion of both robots is always coordinated, while simultaneously supporting the ability to flexibly animate individual robots–or individual parts of the robot, like the mouth and eyes.

Over the past nine months, we explored a few different kinds of collaborative locomotion approaches. The GIFs below show some early attempts at riding a tricycle, skateboarding, and pushing a crate. In each case, the idea is for a robotic character to eventually collaborate with another robotic system that helps bring that character’s motions to life in a stable and repeatable way.

Disney hopes that their Judy Hopps robot will soon be able to use the help of a robotic tricycle, crate, or skateboard to enable new forms of locomotion.Morgan Pope

This demo with Duke Weaselton and his kiosk is just the beginning, says Principal R&D Imagineer Tony Dohi, who leads the project for us. “Ultimately, what we showed today is an important step towards a bigger vision. This project is laying the groundwork for robots that can interact with each other in surprising and emotionally satisfying ways. Today it’s a character and a kiosk, but moving forward we want to have multiple characters that can engage with each other and with our guests.”

Walt Disney Imagineering R&D is exploring a multi-pronged development strategy for our robotic characters. Engaging character demonstrations like Duke Weasleton focus on quickly prototyping complete experiences using immediately accessible techniques. In parallel, our research group is developing new technologies and capabilities that become the building blocks for both elevating existing experiences, and designing and delivering completely new shows. The robotics team led by Moritz Bächer shared one such building block–embodied in a highly expressive and stylized robotic walking character–at IROS in October. The capabilities demonstrated there can eventually be used to help robots like Duke Weaselton perform more flexibly, more reliably, and more spectacularly.

“Authentic character demonstrations are useful because they help inform what tools are the most valuable for us to develop,” explains Bächer. “In the end our goal is to create tools that enable our teams to produce and deliver these shows rapidly and efficiently.” This ties back to the fundamental technical idea behind the Duke Weaselton show moment–collaboration is key!