In 2005, I was embedded as an independent journalist with a platoon of Marines with an attachment of Afghan security forces in the Hindu Kush, just a few miles from the Pakistani border. I was about to step into a possible death trap, and I’d never felt more scared in my life. “There are 50 Taliban massed behind that ridge,” said “Sultan,” our Afghan interpreter (his real name is being withheld for security reasons). He had picked up chatter from his hand-held radio. “They know we’re here,” he continued, “and that we have to cross that field.”
“Time to get moving,” a nearby Marine said.
We began to move, navigating the terraces on the outskirts of a small village. An hour later, we regrouped by a mosque. No attack came; we later learned that the “chatter” was one person transmitting fake orders to fake fighters—a common ploy to confuse U.S. and coalition troops. Back at the Marines’ base, I asked about UAVs (unmanned aerial vehicles) the Marines could have used for reconnaissance in that situation to confirm the warning, had fighters actually been gathering to attack.
“Yes, we have them,” said First Lieutenant Patrick Kinser, the platoon commander. “Never use them, though. They often end up being recovery operations—sometimes dangerous recovery ops.” Kinser was talking about the two Dragon Eye UAVs that his platoon had been given—and had to chase down a number of times in the steep mountains around the base, after they crashed. “And the image quality is terrible.” Kinser said that even the slightest mountain winds made the UAVs’ video feed too jerky to identify much of anything on the ground. “Can’t make out anything of use, really,” he continued. “I once joked we should just fly them both into a tree, so we’d never again have to chase them down.”
The Dragon Eye, while slightly larger than a truly “backpackable” UAV, was also cumbersome to launch: Either it required a bungee cord, or one of the grunts had to throw it hard while running, exposing himself to potential enemy fire.
Five years after my experience in Afghanistan, I visited the Marine Corps Mountain Warfare Training Center in California’s Sierra Nevada mountains. I wanted to know if the instructors had any experience with a small UAV that was capable of enduring mountain and desert flight. They had not, although they mentioned the Dragon Eye, and the related RQ-11 Raven, but noted that neither was compact enough to be backpackable. They had hopes for micro air vehicles that they’d read about, but most were fixed-wing.
“Think of urban fighting,” said Sergeant Tony Powers, one of the instructors and a Marine scout sniper. “That’s when a squad could really use a micro UAV to get eyes on an enemy position. But a fixed-wing platform flies too fast, and isn’t maneuverable in those tight confines.” According to Powers, the most useful platform for such situations is one that can move in any direction, quickly or slowly, then go into a hover and pass video feed back to the user—perhaps a micro-helicopter UAV.
So began my UAV project. Like aircraft homebuilders whose requirements couldn’t quite be met by the kits or plans on the market, I wanted to construct a UAV optimized for a set of tasks that my experience with the Marines suggested. Here are the steps I took to create the Kestrel-6, named after the bird of prey, known for its hovering ability. (The “6” came from the atomic number of carbon and the number of motors used on the craft.) The entire project cost roughly $3,500.
Step 1: Age-old aviation question: Speed or loiter capability?
I chose a multi-rotor aircraft over a fixed-wing or helicopter because I wanted to be able to get a static view. Multi-rotor aircraft are also fast, very stable, and able to launch vertically in the tightest of confines—even inside a room and out a window.
Multi-rotors typically use anything from three motor-propeller assemblies to eight, mounted at the end of arms that are centrally interconnected. I chose the “Y6” configuration, composed of three motor-mount arms with two co-axially mounted motor-propeller assemblies at the end of each arm. With two motors per thrust point (one facing up as a “tractor,” and one down as a “pusher”), the Y6 has redundancy. Because it has only three arms, it gives a mounted camera a wide field of view. I needed the UAV to be as small and stable as possible. Smaller fixed-wing UAVs often fly “squirrelly,” but that’s not true of a well-designed Y6, with its multiple points of thrust stabilized by a high-performance flight control computer.