Every weekend, light buzzing can be heard over Buder Park as drones take flight. Pilots with the St. Louis FPV [First Person View] Racers fly from “12 noon until we run out of batteries.” About once a month, they race through courses full of twists and turns, testing homebuilt quadcopters running on open-source technology. Armando Gallegos has won multiple races and often builds new drones. As he says, “If you’re gonna race, you’re gonna crash.” Here’s a closer look at one of Gallegos’ quadcopters.
1. Frequency: The transmitter and video must run on different frequencies. The controller uses 2.4 GHz to send signals to the antenna. The video transmitter sends video on a 5.8 GHz bandwidth.
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2. The Brain: The proportional integral derivative controller, or PID, “is basically the brain,” says Gallegos. “The controller is trying to kill error”—that is, oscillations or shakes—and to correct the drone’s trajectory. The PID can be tuned to improve drone stability and speed. “The flight controller translates your inputs into a signal,” which controls battery power to the motor.
DEFINING PID: What exactly, is PID? It’s composed of three algorithms: 1. The proportional term, which measures distance from error and tries to decrease it to zero; 2. the integral term, or accumulated error over time; and 3. the derivative term, or rate that error is increasing. At a minimum, a PID needs a gyroscope to monitor the drone’s “angle in space” and then to adjust accordingly. An accelerometer can also help measure speed—“but we typically don’t use those,” says Gallegos, adding that they’re more common on larger drones used for aerial photography.
3. FPV Goggles: Pilots wear first-person view goggles to steer the drones through the course. The maximum video transmitter range tends to be around 1.5 miles.
4. Speed: Race pace is typically 60 mph. Drones can’t always fly at full speed for two minutes—the duration of a race—but the track includes gates that require changes in speed and direction. As of July, the fastest a quadcopter has flown is 163.5 mph.
5. Movement: The torque of the motors controls yaw (twisting on a vertical axis); the pairing of propellers causes pitch and roll. Some drone autopilots limit drone maneuver angles; others are more flexible. “This thing can do a 180 as fast as you tell it to do one,” Gallegos says.
6. Range: The maximum antenna transmission range is 6 miles for Gallegos’ controller, a Crossfire. (Other antennas have higher latency—longer lag between controller input and the drone’s response.) Normally, drones can’t legally fly higher than 400 feet because of Federal Aviation Administration restrictions.
