Drones in Confinement

This entry is part 4 of 7 in the series May 2021

From warehouses to underground facilities, demand for drone inspections in GPS-denied places is rising. The new flying destination for UAVs is the great indoors.

The perfect combination of sun, sand, and sea makes Barcelona one of Spain’s most visited cities. Yet this same combo also takes a serious toll on the city’s sewer infrastructure. Intense heat during the summer can cause pipes to warp. And when the storm season comes, strong waves from the Mediterranean Sea push water and sand inland, putting sewer lines at risk of damage.

To check that the city’s sewage system is in good condition, Aigües de Barcelona, the utilities company that manages the water and sanitation services in the metropolis, has been utilizing the latest aerial technology and brought it underground: drones.

In January 2017, for example, when an important wastewater interceptor pipe broke during a storm, the company tapped an indoor drone to inspect the damage below the streets. Usually, a team of inspectors is sent down the sewers to determine the exact location of the problem.

But the pipe, which measures three meters (about 10 feet) in diameter, was flowing with sewage at 500 cubic meters per second. Mobilizing people in that risky situation was out of the question.

Instead Elios, an indoor drone made by the Swiss company Flyability, was dispatched to do the job. Gliding down the sewers, the drone surveyed the pipes and collected video footage to view the extent of the breakage.

“The entire process lasted approximately an hour, from the time that the drone equipment was prepared, to the actual capture of images and their validation,” says Pol Harder, a UAV pilot with Aquatec and Flind, the company that operated the indoor drone during the sewage inspection.

With the underground images collected by Elios, engineers were able to immediately repair the damaged pipe, stopping the flow of waste into the sea.

Buzzing Indoor Market

At the time Elios was used to inspect the sewage situation in Barcelona, indoor drone services were not yet widely available. Today, there is a growing industry that focuses on this market segment, disrupting the way businesses inspect their indoor infrastructure.

“Our company first started doing drone-based inspections of sewer networks. Now we fly in all kinds of confined spaces,” says Harder.

Although direct market data on indoor drones is not available separately, useful information can be gleaned from the global growth of commercial drones in the past year. According to a report of Drone Industry Insights (DII), a UAV business research firm, the commercial drone sector generated $22.5 billion in 2020 and will increase at an annual compound growth rate of 13.8 percent.

Highlighted in the same report is the rapid growth for the use of drones in the inspection and maintenance of infrastructure, especially in the energy, transport, and warehousing industries.

Meanwhile, analysts from Goldman Sachs, another industry observer, have forecast that the market opportunity for drones is now worth $100 billion, citing increasing demand for UAV-related jobs in construction, utilities, pipelines, and mining.

And indeed, indoor drones have already found a niche in these sectors.

According to Zacc Dukowitz of Flyability, the company’s main market is in industrial inspection. “Our indoor drones are being used to inspect power generation, oil and gas, and maritime infrastructure, thus helping people avoid going into dangerous and confined spaces,” he says.

But it is not only underground where these specialized drones are buzzing. Indoor drones are also particularly handy in the logistics industry.

For example, Ware, a San Francisco-based technology startup, is betting on “the power of drones to transform the way warehouses and distribution centers accomplish the critical task of tracking inventory,” according to its website. The company is focusing on deploying self-flying drones that can capture images inside warehouses and analyze product barcodes using machine-learning tech­nology. Investors have taken notice and have backed Ware’s indoor drone tech­nology with $2.5 million in seed-round funding last year.

Another interesting, though challenging, sector for indoor drone inspection is bridges. By law, all of the more than 600,000 bridges in the U.S. need to be inspected regularly to ensure the safety of the traveling public. Although these structures may not be totally GPS-denied, inspecting them with drones is usually tricky because the GPS signal inside their metal framework is unstable.

Taking up this challenge is an indoor drone company, Digital Aerolus from Kansas. The company’s proprietary solution is to use “advanced mathematics to enable the aircraft to remain ultra-stable without GPS or external sensors” while performing bridge inspection missions.

The company is also applying that technology to meet current needs. At the height of the COVID-19 pandemic last year, it launched the world’s first indoor drone that uses C-band ultraviolet (UVC) energy to disinfect hospitals, retail stores, and other indoor public spaces that are similarly GPS-denied.

No GPS, No Problem

Traditional UAVs rely on global navigation systems such as GPS to provide inflight positioning and velocity information. But in environments where GNSS signal is weak or non-existent, the customary outdoor navigation system cannot be used by indoor drones.

Rather than GPS, indoor drones count on various sensors for stabilization and navigation while moving inside confined places. Miniature inertial sensors are at the heart of all indoor drones, providing information on its 3D-orientation, position, and speed. And to avoid obstacles such as walls, posts, and humans, these flying machines are either equipped with cameras, infrared, sonar, or a combination of these sensors. More advanced indoor drones are now using fully automated simultaneous localization and mapping (SLAM) systems based on lidar.

For example, Digital Aerolus’s Aertos 130IR drone relies on nine advanced external sensing elements, including omnidirectional scene sensors, to provide inflight stability while measuring dis­tances and tracking the environment. This patented approach allows the drone to self-correct during flight.

Flyability, on the other hand, uses vision and distance sensors as well as manual controls to maneuver its indoor drone in confined spaces. A wireless radio link between the drone and the human operators is provided by a ground control system, allowing them to manually control the movement of the aircraft and direct the video camera to its target.

Things that Bump Inflight

Impacts from collisions are, however, unavoidable in constricted spaces. So aside from sensors, the structure of indoor drones must be built with strong materials to withstand occasional bumps.

The spherical cage that protects the Flyability drone is made from carbon fiber and its lattice structure makes the drone relatively light. Even with a diameter of about 40 centimeters (15.7 inches), its total takeoff weight is only 700 grams (1.54 pounds).

“I have seen how the drone’s protective cage has given us big security when entering many spaces, allowing us to get really close to the elements being inspected,” says Harder.

Digital Aerolus also uses carbon fiber. It’s the main material for its drone, which has a ducted-design to provide protection to its four propellers. The duct-covered blades are especially suitable when it has to fly in structures where the drone could bump into steel and cement. Measuring just 53.3 centimeters (21 inches) from edge to edge, the Digital Aerolus drone looks tough and sturdy. But it is also heavy, weighing in at 2.7 kilograms (5.95 pounds).

In other places where indoor drones must be light and more compact to do their job, a smarter approach is to rely on robust software, such as artificial intelligence (AI) technology to quickly dodge through any stumbling block.

Ware, for example, has turned to Skydio, an American company that makes fully autonomous UAVs with 360-degree obstacle avoidance capability. The Skydio drone is small and light (27 centimeters wide, 775 grams) but is well-equipped to capture images of inventory in cramped warehouses.

During flight, its six 4K cameras build a 3D map of the surroundings, then deep learning algorithms classify the objects in the images, while advanced AI makes smart decisions to avoid obstacles. All this is done in real-time.

Better Workflows

Thanks to better software and vast improvements in sensors and processing technology, indoor drones are becoming part of many business applications, while at the same time introducing improvements in already existing workflows.

The ability of indoor drones to reach GPS-denied environments and confined spaces is clearly its greatest advantage. Because of this feature, visual inspections can now be done in almost any off-grid place. Also, better camera payloads can now scrutinize dark and crampy corners. What used to be a laborious and risky process, detailed visual inspection of large infrastructures, is now faster and safer.

Speed and security are thus the main selling points of incorporating indoor drones in workflows. In places where it would be time-consuming and dangerous to send a person to conduct a visual inspection, indoor drones can be immediately deployed to accomplish the task, thereby cutting costs for companies while reducing risks to manpower.

“Our customers are always looking for ways to improve safety and efficiency in their operations,” says Dukowitz of Flyability. “Our indoor solution allows them to collect visual data without sending a person into a potentially dangerous space.”

And how about flying regulations? Specific rules vary depending on the country where you intend to use indoor drones. For example, aviation authorities in the U.S. and Europe do not consider enclosed spaces as part of their “national airspace,” meaning both recreational and licensed pilots can fly their UAVs indoors. But it’s always good to check if rules for indoor flying have changed before operating in your area.

Vroom for Improvement

Yet, despite the boom in the indoor drone market, manu­facturers can still enhance some much-needed features, in particular the longevity of lithium-ion batteries that provide power to drones.

UAVs are limited by their battery life, hampering their flight time, and consequently reducing the number of applications where they can be practically used. Currently available indoor drones only have an average flight time of 10 to 20 minutes, while their outdoor counterparts have already gone beyond that duration. Some have even reached 55 minutes in the air.

Equipping indoor drones with bigger batteries that are more powerful, however, might not be the solution if they have to stay light and nimble in the air. One option could be NASA’s wireless power transmission technology, a novel approach of remotely beaming power to UAVs via laser or infrared. But this is still years away from becoming available commercially.

And while attaching multiple sensors and better processing power make indoor drones useful to various industries, packing more of them would also mean consuming more power from the UAV’s battery pack. The drone’s total payload weight would become heavier, too, triggering the propellers to work even more to maintain flight, and causing the battery to drain faster.

And lastly, there is the important aspect of maintaining signal between the indoor drone and the ground station while maneuvering inside confined spaces. Human operators control the drone’s movement and direct the camera via radio, Wi-Fi, or Bluetooth signals. Data is also transmitted through wireless signals.

“We always fly our indoor drone as far away as the battery or the signal lets us,” says Harder. “They are the weakest elements of the hardware.”

Still, as a professional drone pilot since 2017, Harder is optimistic and sees plenty of potential for enhancing the capabilities indoor drones in the future.

“The drone market is constantly changing,” he observes. “The key to improving indoor drones is to have a company with a strong R&D and who listens to the customer feedback.”

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