Postgraduate student designs and builds a hybrid quadcopter

[Article by Amber Viviers]

Since building a clap-clap switch at his student residence room and a voice-controlled home automation system, Waldo Wessels, a postgraduate student at the Faculty of Engineering, was ready to research, design and build a novel quadcopter as part of his research for a master’s degree in the field of Mechatronics, Robotics and Automation Engineering.

The research topic, “Design, Build and Test a Quadcopter with a Novel Configuration for Endurance Flights”, was proposed by Dr Willie Smit: Senior Lecturer in the Division for Design and Mechatronics at the Department of Mechanical and Mechatronic Engineering.

Waldo first had to do some theoretical calculations as people in the industry doubted that the design would work. “I first had to ascertain that the drone would be able to fly and whether the design was a step ahead of the existing quadcopter designs,” he says.

Initially, the quadcopter was only meant to be driven by electrical motors. However, his theoretical power calculations proved that a petrol engine would maximise flight times. The quadcopter became a hybrid quadcopter.

Waldo developed a passion for design when he received a soldering iron from his grandfather in Grade 1, which inspired him to become an engineer. After graduating with his undergraduate degree in Mechatronic Engineering, he wanted to improve and put his skills in electronic and mechanical engineering to the test.

He says about the design: “Since the large central propeller is responsible for producing most of the lift in this novel configuration, and because rapid differential thrust variations are not required for roll, pitch and yaw, the large propeller was powered by a petrol engine. The electric motors were canted horizontally at a fixed angle to counteract the counter torque like a conventional helicopter’s tail rotor. The small electric motors are responsible for roll, pitch and yaw control and stability.”

Parts can be easily removed, fixed, and replaced.

Although designed to fit a camera in front of the quadcopter, time constraints prevented the installation of a GPS and camera. For now, a standard quadcopter remote control is used instead of GPS.

Because of its chemical resistance to petrol, the airframe comprises carbon fiber tubes, plates, and 3D printed joints, printed from polyethylene terephthalate glycol (PETG). Low-density polyethylene foam rods used in the landing gear were an additional benefit that acted as shock absorbers during hard landings.

Weighing 5.5 kg with the battery and a full petrol tank, the drone becomes lighter while flying and using petrol, making it more efficient.

Waldo says the main engine (which creates most of the lift) is a 20cc 2-stroke engine, and a 17×6 inch carbon fiber propeller and carbon fiber tubes were purchased locally but mainly sourced from overseas. He used three brushless DC motors with polycarbonate propellers as they have double the lifespan of brushed DC motors. A standard Pixhawk 4 flight controller, a lithium polymer battery, and electronic speed controllers were among the components required to complete his project.

Assembling was effortless and fast but waiting for some of the parts, especially the petrol engine (purchased during Covid-19), took frustratingly long.

Asked what type of drone it is, Waldo says: “Despite the novel configuration, it is still a quadcopter due to its four fixed pitch rotors. Because of the centre propeller’s counter torque, the drone’s landing gear required a unique design, as normal quadcopter landing gear would have caused this quadcopter to tip over during take-off. A circular polypropylene tube at the base allowed the drone to slide on the take-off surface, which solved the problem and ensured take off with ease.”

Despite the noisy engine, the drone can be used for search and rescue, package deliveries, agriculture, and much more.

Waldo praises his supervisor, Dr Smit, and other lecturers who shared their knowledge. He learned through the problem-solving the project presented and thoroughly enjoyed the practical component of the research.

Photograph: Waldo Wessels proudly exhibits the hybrid quadcopter.