This Innovative Tricopter Drone Can Fly with Just a Single Motor Active

VTOL drones

When picturing a drone, the most common image people think of probably involves four fixed arms that protrude from a central body, each with their own motor sat atop the end. In this configuration, the aircraft can take off vertically and then fly around by tilting to one side and accelerating in that direction. Going even further, making minor tweaks to the speed and timings of the propellers can produce incredibly complex motions. However, losing even a single motor will result in a disaster, as the drone can no longer balance properly.

Nicholas Rehm has created a newer design that does away with the horizontally fixed struts and substitutes them for a set of three variable-angle wings, creating an aircraft that functions almost entirely as a single large propeller. This tricopter setup allows for the drone to stay in the air with just one of its three motors working, leading to amazing improvements for maximizing safety and durability.

The spinning problem

Unlike a more traditional quad/hex/octo-copter, this setup can operate either in a traditional "drone" mode, in which the craft is devoid of any rotation, or in a spinning mode wherein multiple motors can be lost simultaneously. One glaring issue is that when spinning, the drone loses any semblance of a frontal direction, which means the operator would need to input small adjustments many times per second. To address this, Rehm loaded some new code onto his Teensy-based flight controller that continually checks the current heading from the IMU and updates the LEDs on the tip of each wing to illuminate whenever that wing is facing towards the front. Just like a persistence-of-vision (POV) display, it had the effect of creating a narrow band of light in only a single direction, no matter how quickly the drone was spinning.

Adjusting the direction

With the flight controller now able to determine where the craft is oriented, Rehm then needed a way to turn and pitch the done. The periodic nature means each motor only needs to be accelerating on one half of the plane and decreasing when it reaches the other half. Changing the amplitude of this wave adjusts how much roll is created, while adding the cosine of the wave along with another coefficient adjusts the degree of pitch.

Testing it out

After testing the drone to ensure it responds correctly to pitch and roll inputs from the joystick, Rehm brought it outside for its first flight where it performed extremely well. Although there was some wobbling when two of the three motors were shut down, he was still able to safely lower it to the ground, unlike a more traditional design. In the future, Rehm might create other variants such as an X-wing or fixed-fuselage prototype. To see more, you can watch his demonstration video here on YouTube.