Tether created for DJI Inspire
A television professional who provides satellite trucks for the Super Bowl and other events has created a custom tether that supplies power and collects video from a DJI Inspire in flight, allowing the quadcopter to remain aloft indefinitely (until it rains, at least). The $12,000 system includes a custom ground station created with broadcast television in mind, though customers have found other applications too: At least one farmer uses it to keep an eye on his cattle.
Charles Spoto, owner of Satellite Technology Systems, provider of live television feeds for Super Bowl games from 2007 forward, and a frequent contractor to major networks, said in a telephone interview that despite years of radio-controlled flying as a hobby, it took a while before he developed an interest in drones.
“The problem with live TV and drones is a lot of networks don’t want to be live with the drone because they don’t want to become part of the story,” Spoto said. “A tethered drone seemed to be something that would be more adequate for being live, and have some protection… some restriction. Being live and tethered do go together for news and sports.”
Spoto is no stranger to electronics, or radio control systems, or tinkering. He has built turbine engines for RC models, among other things. He had a notion that tethering a drone would solve more than one problem at once: the relatively limited battery life (about 20 minutes) of most small camera drones, and their potential to cause injury or damage if the operator loses control.
“I decided to make a system for our services, and secondly for the marketplace,” Spoto said.
The PowerLine Tethered System Spoto and his team created is made specifically for the DJI Inspire 1, among the most popular platforms used by commercial operators and hobbyists who want a high-end system. The Inspire can carry a range of cameras, including thermal cameras, another model that features a powerful zoom lens designed for search and inspection, and the Zenmuse X3 and X5 cameras that are more typically sold with the system.
“I wanted to use a UAV that is standard in the industry,” Spoto said. “I wanted a mainstay, and of course DJI is ruling the roost, as we know, and they do have some good equipment in the marketplace.”
Spoto and his team needed about two months to create a prototype. DJI did not provide any technical assistance, nor did they ask the company to reveal source code. They had to figure out on their own how to make their electronics communicate effectively with the drone electronics, building a station that transmits power to and collects video from the drone in real time.
Included in the firmware that runs the aircraft is a safety feature that forces a landing after a set amount of time, to prevent users from running out of power and crashing. Convincing the drone that there was plenty of power coming through a tether was the largest challenge, Spoto said; the rest was relatively simple. He has secured a provisional patent for the system.
The portable ground station packed in a heavy-duty case for transport and easy deployment connects to the custom-made tether, which is stored on a reel. Inside that 200-foot line is a Kevlar strand giving the tether strength to withstand a 100-pound load (the drone weighs just over 9 pounds, including the on-board aircraft interface, with small variations depending on camera configuration).
Spoto said the system does not alter the aircraft's center of gravity, and he has tested it in 110-degree-Fahrenheit desert heat, noting that the power supply and electric motors increased in operating temperature by only 11 degrees.
“They just run and run and run,” Spoto said of the Inspire’s motors, noting that they include bearings that have held up in other applications for 10,000 continuous hours or more.
Spoto said he has logged hundreds of hours testing the system in a variety of conditions, keeping careful notes in case an opportunity arises for the FAA to consider more permissive treatment of tethered drones than their free-range counterparts. Restrictions imposed by Part 107 include prohibition of flights over people or in controlled airspace, which can be waived; the FAA has made clear the agency does not consider a tethered drone to be different from a non-tethered drone for purposes of compliance.
Spoto has priced the basic system, including ground station, power supply, tether, and drone interface, at $12,000, and $15,000 including a broadcast standard cross converter and monitor. He is developing a similar system for smaller DJI drone models, including Phantom and Mavic.
In addition to broadcast television producers, Spoto is marketing the PowerLine system to public safety agencies that have uses for a persistent surveillance capability, military customers, and others who have uses that Spoto did not envision.
“We had a customer purchase the system for a large cattle ranch… he wanted to send up his drone to view where his cattle are,” Spoto said. “He can leave it up for many, many hours. Those cattle move."
Spoto said zoom cameras like the Zenmuse Z30 turn a tethered Inspire into a powerful surveillance tool, albeit one that is firmly leashed to the ground. A tethered drone can watch the herd, hovering at the end of a 200-foot cable until those cows come home.
