The full potential of quadcopter drones has not yet been realized. A major reason for that is energy efficiency. Constantly spinning rotors provide excellent control over an aerial vehicle, but they also require a lot of energy. However, the more batteries you pack on a drone, the heavier it gets. And the heavier it gets, the more energy you need to keep it airborne. See the problem?
Daniel Riley recently set out to solve this problem in a counterintuitive way: by making a drone that is abnormally large. This does add additional weight, of course. But as it turns out, if the vehicle is carefully designed, it can also improve its flight efficiency.
A closer look at a single rotor (📷: Daniel Riley)
Riley’s design is based on the concept of low disc loading — maximizing the total rotor area relative to the drone’s weight. Instead of relying on small, high-speed propellers, his machine uses enormous 41-inch blades that spin at a remarkably low 350 to 500 RPM. This approach reduces the energy required to generate lift, but it introduces a new challenge: how to maintain control without rapidly adjusting motor speeds.
The solution is a variable-pitch system more commonly found in helicopters than hobby drones. Each rotor is equipped with a mechanism that allows the blade angle to change dynamically during flight. High-torque servos mounted at the base of each arm adjust the pitch through a pushrod running inside a hollow carbon fiber shaft. This allows the drone to maintain a constant motor speed while using blade pitch for rapid stabilization.
To make this possible, Riley combined off-the-shelf and custom components. Four relatively small 5010 360KV “pancake” motors provide torque, but they are paired with a large belt-driven reduction system. A 22-tooth pulley on the motor drives a 165-tooth pulley on the propeller shaft, multiplying torque and enabling the motors to spin the oversized blades efficiently.
Going for a test flight (📷: Daniel Riley)
The frame itself is a mix of carbon fiber tubes and 3D-printed polycarbonate parts, designed for both strength and modularity. Even the propellers were fabricated in sections using PETG and reinforced with carbon rods. Weight savings were critical throughout the build, leading Riley to remove bulky heat sinks from the motor controllers and encapsulate them in epoxy instead.
During hover tests, the drone achieved approximately 18.1 grams of thrust per watt — about 1.5 times more efficient than a typical high-efficiency quadcopter. However, this efficiency comes with trade-offs. The massive blades have significant rotational inertia, making traditional motor-speed-based stabilization too slow. Instead, the flight controller treats the pitch servos as the primary control system.
An experimental auto-rotation test highlighted another limitation. While the drone could descend slowly thanks to its large rotor area, it lacked the passive stability needed to remain upright without active control, ultimately leading to a crash.
Even so, Riley’s project demonstrates a potential new direction for drone design. By scaling up and rethinking how lift and control are achieved, it may be possible to build aerial systems that stay in the air far longer than today’s machines.
