Even now, as James Goppert looks across 20,000 square feet inside Hangar 4 at the Purdue University airport, he still can't quite believe what has been done.

The 50 Qualisys motion capture cameras mounted on beams on the ceiling, precisely tracking movement below to the millimeter.

The 10 cameras mounted on tripods, perfectly placed to augment the ceiling cameras and exactly angled to capture the unmanned aerial vehicles (UAVs) zipping around the facility, weaving in and out of a scaled urban environment.

The swarm of miniature Crazyflie drones at his disposal, from Bitcraze with state-of-the-art active motion capture boards from Qualisys.

The graduate students conducting research, gathering data and building algorithms on laptops and then seeing those algorithms played out in real time, right in front of them, in the motion capture environment.

The aeronautical and astronautical engineers intermingling with computer science majors, aviation technology students popping in to test drones, mixing with electrical engineering students, providing the ultimate multidisciplinary environment.

It's everyday life in one of the most unique university facilities in the country.

There's no other university facility quite like this one. From its precise motion capture system, down to 1mm, to its unobstructed space in Hangar 4, the Purdue UAS Research and Test (PURT) Facility offers unparalleled technology in support of the largest indoor motion capture system in the world. Photo by - Rebecca McElhoe, Purdue University.

The Purdue UAS Research and Test Facility (PURT) is the largest indoor motion capture system in the world and offers novel capabilities to match: In its 100-feet-by-180-feet contiguous volume, in totality of camera coverage, in the preciseness of those cameras, in its ability to not only fly large swarms of drones but also simulate hundreds more with virtual reality, in its ability to create simulated images for VR and augmented reality to construct mixed-reality environments.

"It's got the educational element, as well as a lot of community outreach, and it's also very integral for research," said Goppert (BSAAE '07, MSAAE '11, PHD AAE '18) the facility's managing director.

In 2018, this was only a vision.

EARLY DAYS

Goppert had just completed his PhD work in the School of Aeronautics and Astronautics when he heard about the idea to develop an unmanned aircraft systems (UAS) research and test facility. His industry work in robotics and doctorate work analyzing vulnerabilities in unmanned vehicles and how to successfully detect and counteract them made him an ideal candidate to assist in setting up the facility. Then-head Tom Shih offered Goppert the job, tying in helping to teach dynamics and control courses as well. But being part of the lab played a large role in Goppert staying in West Lafayette.

"As a more practical guy, I get to go in the lab and work with students on hands-on robotics and teach them how to do programming and teach them how to debug when a drone doesn't fly and get the soldering iron out when I have to," Goppert said. "Not many people get to be a managing director of a facility that's across all of Purdue. Even though aero/astro is in charge of it, we collaborate with many other departments in conducting state-of-the-art drone research. I think that's why I love it."

Early on, the idea was to develop a facility that would help Purdue stand out and be unique with an emphasis on project-based learning. But they had to figure out where to put the lab.

It was Shih's idea to look at Hangar 4. The group soon realized it was the "sweet spot" because it had bus access, was the largest facility they could get and had "the really cool atmosphere of being at the airport which all went in to play there," Goppert said.

Goppert investigated what other universities offered, especially ones that had indoor setups, and he soon realized Purdue's location at Hangar 4 could be the largest motion capture indoor environment. As he was looking to secure the equipment, he asked companies if they'd installed anything in this type of square footage before " and how many cameras they'd realistically need to cover such a space.

AAE Professor Inseok Hwang said PURT's novel capabilities have produced research grants that likely wouldn't have been secured without the facility.

By Fall 2019, vendors were coming to West Lafayette from all over the world to offer demonstrations. Goppert brought in the collegiate drone racing team at Purdue to fly around the facility "as fast as possible" to stress test all the camera systems. Ultimately, Swedish company Qualisys won out, in part because they'd shown their cameras could hold up to the conditions in the Midwest's variable temperatures at the University of Michigan's outdoor facility. Even though Purdue's facility is indoors, the hangar is "basically a barn," Goppert said, so the cameras needed to be able to sustain tough conditions and be extremely weatherproof.

And, most importantly, they needed to provide ultimate performance: The lab only was going to be as valuable as the accuracy of its measurements from the motion capture system.

The biggest test came after the first 54 high-resolution cameras were installed on the massive beams and mobile tripods within the hangar. Goppert said Purdue lucked out in that the 1960s hangar was so overbuilt there was very little deflection in the wind. Still, Qualisys was expecting the facility would get calibration errors of around 3 millimeters.

"It turned out we did a lot better than they thought was possible," Goppert said. "As we move this wand around the entire space, all the cameras agree on the solution of where the wand is with a standard deviation of 1 millimeter. That means in that entire space, which is basically half the size of a football field, we can tell where we are down to a millimeter, which is crazy."

And, with that, PURT transformed into an indoor lab no other university can match.

Motion capture enables a lot of robotics and the ability to create the elements. There's an ability to detect when the algorithms are giving the right answer and have a ground truth. That allows researchers to find errors, compare algorithms and know what the right answer is so they can know which algorithm is doing a better job.

Because the facility is indoors, there is no GPS. But the motion capture system and its down-to-the-millimeter precision provides the ability to simulate sensor data inside. It's easy to construct a fake GPS signal that actually degrades and adds some noise like GPS would have.

Its sensors also can simulate video streams, which means instead of a drone having an on-board camera that is seeing what it's actually seeing in the facility, researchers can give it a fake digital camera image that is streamed over Wi-Fi to the vehicles. Then, the vehicles see through "virtual reality goggles" whatever researchers want them to see.

"That allows you to do really cool things where you can make the vehicles think they're in whatever environment you want to, visually or with GPS signals or any other signal we'd want to create and feed to the drone. It's a controlled environment at the same time, which means we don't have to worry about FAA certifications."

RESEARCH

The novel capabilities have produced research grants that likely wouldn't have been secured without the facility.

AAE Professor Inseok Hwang is principal investigator on a three-year, $2.3-million grant from the Technology Innovation Institute in Abu Dhabi to study the application of secure drone swarms in urban environments. Hwang, Goppert and Dongyan Xu, the Samuel D. Conte Professor of Computer Science, were tasked to make sure drones and their systems could operate securely, safely and efficiently in the United Emirates capital.

Being part of PURT played a large role in James Goppert staying in West Lafayette after earning his bachelor's, master's and doctorate degrees in AAE. He's now managing director of the facility. Photo by - Rebecca McElhoe, Purdue University.

The project required expertise in autonomous vehicles, control, sensing, virtual reality and security.

Goppert built a mixed reality environment, combining a virtual reality urban environment with a scaled physical model of the city. The drones fly and navigate the city, and the environment can be programmed to simulate a wide range of settings, including weather, traffic and urban development, to test the drones' applicability and agility.

With autonomy, though, comes risks of hackers and complications between interacting agents. Hwang and Xu have a multitiered approach from the cybersecurity and robustness standpoint. Hwang is developing a mathematical model and using the control theoretical solution approach, assessing potential cyberattacks on the systems and working to design a controller in such a way that the systems becomes more resilient to attacks. Xu is investigating from the cyber perspective of security, encryption, authentication and peer-to-peer communications.

Neither Hwang nor Goppert is aware of any other research being done using mixed reality to this scale.

"The selling point was our facility," Hwang said of the grant. "We're not just developing the algorithms and numerically testing it on a computer. On top of it, we actually fly the vehicle, and real tests can be done. One of the goals is to develop a mixed reality environment where the vehicle actually is flying in empty space but it believes it is flying through a city.

"Such things could not be done before PURT. A small lab could not accommodate that because it doesn't have the scale. But this is a huge indoor facility so we can implement and actually test it so that these sponsors get perspective. They get real results rather than nice movies or nice plots."

Another bonus: Testing can be done with a single vehicle as well as swarms " but not all of the swarms need to be physical drones. Though a larger group of vehicles can be physically flown inside the lab because of its size " especially because the old hangar offers a massive unobstructed space " hundreds could be added through mixed reality.

"An individual faculty member may have a small lab, but they can only fly a small number of drones. But this can accommodate up to 100, and even more because we have a mixed reality," Hwang said. "There may be 50 physical vehicles actually flying, for example, with an additional 250 vehicles flying in the virtual environments, harmoniously together. The number of the vehicles, there's not any limit there. Not everything is a simulated environment, but a significant portion actually fly."

A scaled urban environment also will play a key role in Purdue's work on the multidisciplinary team selected by NASA's Aeronautics Research Mission Directorate grant through its University Leadership Initiative program. Purdue's group, which received about $2 million of the team's $8-million grant, targeted the "secure and safe assured autonomy" thrust, and the team's topic is "Assured Autonomy for Aviation Transformation."

Purdue work is focusing on innovations in secure and robust distributed autonomy and control algorithms applicable to both cargo and future passenger carrying advanced air mobility, said AAE Professor Daniel DeLaurentis, Purdue's PI on the project.

As vehicles are made more autonomous, they also need to be safe and more robust. Goppert's piece is looking specifically at model checking and verification and validation of the auto-pilot software for the vehicles.

"When they fly downtown, they're around buildings. As wind gusts increase, how do you quickly and safely plan trajectories for these vehicles and determine when it's too windy for them to fly?" Goppert said. "To do that in the real world, we'd have to actually have a fleet of vehicles flying around a city. That's not safe or practical to do while you're developing the algorithms. This kind of controlled scaled urban lab setting is a great place to prototype because it can allow us to transition from pure simulation toward final deployment without having to do the leg work of actually flying a fleet of UAVs in a city. We can look at the complex interactions and if the mathematical models we're creating actually are validated in the real world."

Said Hwang, "We built this emulated scaled city environment to test the developed algorithms and what can really go wrong, and it cannot be done in the computer environments yet. So that's another interesting aspect."

FUTURE

Goppert and Hwang plan on continuing to push the possibilities in PURT.

Because of the size of the hangar, Goppert had a senior design class designing airplanes last year that could fly in the facility.

"The ability to actually fly fixed wing aircraft in a motion capture environment is something that's really unique," Goppert said.

Having an open-air wind tunnel is a possibility, too, because the facility is so large and there's a lot of open space to get air flowing. That'd open the possibility to control wind around the objects within the environment. They could inject fog, virtually or by having a dry-ice machine pumping fog into the space.

"Being able to manipulate the environment of the drone like that is very interesting to us," Goppert said.

The size also means vehicles can go fast and don't have to have the largest turning radius. That's not the case in a small building with a motion capture system.

There's certainly more to come.

"It's more impressive than I expected it'd be within a short period of time," Hwang said. "This is a very, very unique facility that belongs to Purdue. It opens up the door for the new grant opportunities, research opportunities and even teaching and educational environments as well, student-led. That's the whole goal."