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How Disney Imagineering Crammed a Humanoid Robot Into a Groot Suit

Project Kiwi is an untethered bipedal humanoid robot that Disney Imagineering designed not just to walk without falling over, but to walk without falling over with some character. At about 0.75 meters tall, Kiwi is a bit bigger than a NAO and a bit smaller than an iCub, and it’s just about completely self-contained, with the tether you see in the video being used for control rather than for power. Kiwi can manage 45 minutes of operating time, which is pretty impressive considering its size and the fact that it incorporates a staggering 50 degrees of freedom, a requirement for lifelike motion.

This version of the robot is just a prototype, and it sounds like there’s plenty to do in terms of hardware optimization to improve efficiency and add sensing and interactivity. The most surprising thing to me is that this is not a stage robot: Disney does plan to have some future version of Kiwi wandering around and interacting directly with park guests, and I’m sure you can imagine how that’s likely to go. Interaction at this level, where there’s a substantial risk of small children tackling your robot with a vicious high-speed hug, could be a uniquely Disney problem for a robot with this level of sophistication. And it’s one of the reasons they needed to build their own robot—when Universal Studios decided to try out a Steampunk Spot, for example, they had to put a fence plus a row of potted plants between it and any potential hugs, because Spot is very much not a hug-safe robot.  

So how the heck do you design a humanoid robot from scratch with personality and safe human interaction in mind? We asked Scott LaValley, Project Kiwi lead, who came to Disney Imagineering by way of Boston Dynamics and some of our favorite robots ever (including RHex, PETMAN, and Atlas), to explain how they pulled it off.

IEEE Spectrum: What are some of the constraints of Disney’s use case that meant you had to develop your own platform from the ground up?

Scott LaValley: First and foremost, we had to consider the packaging constraints. Our robot was always intended to serve as a bipedal character platform capable of taking on the role of a variety of our small-size characters. While we can sometimes take artistic liberties, for the most part, the electromechanical design had to fit within a minimal character profile to allow the robot to be fully themed with shells, skin, and costuming. When determining the scope of the project, a high-performance biped that matched our size constraints just did not exist. 

Equally important was the ability to move with style and personality, or the “emotion of motion.” To really capture a specific character performance, a robotic platform must be capable of motions that range from fast and expressive to extremely slow and nuanced. In our case, this required developing custom high-speed actuators with the necessary torque density to be packaged into the mechanical structure. Each actuator is also equipped with a mechanical clutch and inline torque sensor to support low-stiffness control for compliant interactions and reduced vibration. 

Designing custom hardware also allowed us to include additional joints that are uncommon in humanoid robots. For example, the clavicle and shoulder alone include five degrees of freedom to support a shrug function and an extended configuration space for more natural gestures. We were also able to integrate onboard computing to support interactive behaviors.

What compromises were required to make sure that your robot was not only functional, but also capable of becoming an expressive character?

As mentioned previously, we face serious challenges in terms of packaging and component selection due to the small size and character profile. This has led to a few compromises on the design side. For example, we currently rely on rigid-flex circuit boards to fit our electronics onto the available surface area of our parts without additional cables or connectors. Unfortunately, these boards are harder to design and manufacture than standard rigid boards, increasing complexity, cost, and build time. We might also consider increasing the size of the hip and knee actuators if they no longer needed to fit within a themed costume.

Designing a reliable walking robot is in itself a significant challenge, but adding style and personality to each motion is a new layer of complexity. From a software perspective, we spend a significant amount of time developing motion planning and animation tools that allow animators to author stylized gaits, gestures, and expressions for physical characters. Unfortunately, unlike on-screen characters, we do not have the option to bend the laws of physics and must validate each motion through simulation. As a result, we are currently limited to stylized walking and dancing on mostly flat ground, but we hope to be skipping up stairs in the future!

Of course, there is always more that can be done to better match the performance you would expect from a character. We are excited about some things we have in the pipeline, including a next generation lower body and an improved locomotion planner.

How are you going to make this robot safe for guests to be around?

First let us say, we take safety extremely seriously, and it is a top priority for any Disney experience. Ultimately, we do intend to allow interactions with guests of all ages, but it will take a measured process to get there. Proper safety evaluation is a big part of productizing any Research & Development project, and we plan to conduct playtests with our Imagineers, cast members and guests along the way. Their feedback will help determine exactly what an experience with a robotic character will look like once implemented.

From a design standpoint, we believe that small characters are the safest type of biped for human-robot interaction due to their reduced weight and low center of mass. We are also employing compliant control strategies to ensure that the robot’s actuators are torque-limited and backdrivable. Perception and behavior design may also play a key role, but in the end, we will rely on proper show design to permit a safe level of interaction as the technology evolves.

What do you think other roboticists working on legged systems could learn from Project Kiwi?

We are often inspired by other roboticists working on legged systems ourselves but would be happy to share some lessons learned. Remember that robotics is fundamentally interdisciplinary, and a good team typically consists of a mix of hardware and software engineers in close collaboration. In our experience, however, artists and animators play an equally valuable role in bringing a new vision to life. We often pull in ideas from the character animation and game development world, and while robotic characters are far more constrained than their virtual counterparts, we are solving many of the same problems. Another tip is to leverage motion studies (either through animation, motion capture, and/or simulation tools) early in the design process to generate performance-driven requirements for any new robot.

Now that Project Kiwi has de-stealthed, I hope the Disney Imagineering folks will be able to be a little more open with all of the sweet goo inside of the fuzzy skin of this metaphor that has stopped making sense. Meeting a new humanoid robot is always exciting, and the approach here (with its technical capability combined with an emphasis on character and interaction) is totally unique. And if they need anyone to test Kiwi’s huggability, I volunteer! You know, for science.