ThinKing January 2021 - Lightweight Hercules: Quadrocopter trimmed down by two thirds, but carries four times its own weight



The ThinKing for January will honour two students from the Pforzheim University of Applied Sciences who applied their knowledge from different disciplines consistently and turned a university project into true lightweight construction success thanks to their perseverance and inventive ambition. The quadrocopter was trimmed down to a lightweight construction, losing 60% of its mass yet able to carry four times its own weight.

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The Baden-Württemberg State Agency for Lightweight Construction will be presenting the ThinKing for this innovation in January 2021. Each month, the Leichtbau BW GmbH awards this label to provide a platform for innovative lightweight construction products or services from Baden-Württemberg.

At a glance:

  • Functional integration: The drone's cantilever arms are integrated into the base plate.
  • 3D printing: The board is only as large as necessary, and made of PLA via additive manufacturing.
  • Multiple effects of lightweight construction: The smaller battery weighs just a third of the original weight.
  • Careful sourcing: The carefully selected purchased parts weigh around a third less.

“The first drone weighed 1.5 kg and was much too heavy, almost unable to fly” says Marc Schulz, describing the starting point for his bachelor's thesis, which he completed alongside Ken Noé over the last six months as they developed this drone into a lightweight quadrocopter. The two students are graduates of the Bachelor's program in “Mechanical engineering/Product development” and are currently in the Master’s program in “Mechatronic system development”. “Electronics, control, regulation and display technology, software development, IT, circuit board production, lightweight construction and additive manufacturing – really, every single thing we learned about in our whole program is in this development” says Noé excitedly.

Redesign with FEM analysis

Both of them are proud to say that an initial redesign of the base plate helped them make the most progress in reducing the weight. “In the first drone we didn’t use a large amount of the base plate surface” Schulz says. Therefore, the new geometry was restricted to only the necessary area – one unique highlight is that the cantilever arms are already integrated into the plate itself. The other required screw connections – and their unnecessary mass – were eliminated. Assembling the drone went much quicker thanks to the small number of parts involved. PLA was used to build the current, 3D printed base plate in the lightweight construction quadrocopter. The necessary cable outlets and other openings on the plate were integrated during the manufacturing process, thanks to the additive manufacturing applied. An FEM analysis of the base plate with cantilever arms clearly showed that the areas where the arms meet the board are exposed to the highest loads and must be stabilised through rounded areas and openings. The small battery saves even more weight. It contributes around 22 percent, a significant weight reduction, and has another typical effect for lightweight construction: Reducing the mass of material moved allows for significant energy savings. Sourcing for the purchased parts focused on lightweight design, resulting in additional weight savings. The feet of the drone – previously compound springs with attachments – were replaced by lightweight hollow aluminium profiles that connect the top and base plates as well. The current version now includes state-of-the-art technology for lightweight multicopters, including connection technology, cable openings and soldering points, as well as purchased parts.

Control technology - workhorses in and out of the laboratory

Since the task for their Bachelor's thesis was “Developing a multicopter test rig to visualise height control”, the lightweight quadrocopter has sensors and control technology on board, as well as two plain bearings that limit its flight path on the test rig between two rods. There, it will fly up and down to act as a testing laboratory for control technology interactions to future generations of students. The height control on the quadrocopter, for instance, can show precisely how a fault impacts the controls. “The project started during the foundation courses of their bachelor’s program, was continued in a joint bachelor's thesis, and is now even being used to teach younger students, now that the two are also working as research associates at the university during their master’s program” says Professor Peter Heidrich, who advised the students over the last three years. The lightweight quadrocopter from Pforzheim also had another important and unique feature. Currently, the drone has an electromagnet on its base that can be used to transport small loads and drop them at targeted locations. The lift of the 500g lightweight quadrocopter, however, is sufficient to pick up loads four times as heavy as the quadrocopter itself. To utilize this maximum load-bearing capacity, however, the electromagnet needed to be replaced by a gripper.

The fascinating field of lightweight construction

Even after the work was completed, there are still ways to optimise the lightweight construction of the prototype. The material of the base plate could be fibre-reinforced, which would offer better stiffness and therefore further material and weight savings. In addition, overhauling the adapter board and eliminating the Arduino Uno standard components could save additional components and weight, while expanding the functionality of the drone. The electromagnet can also be further improved. “We wanted to start development from the ground up, and understand the difficulties one would face in a lightweight construction project in the different disciplines” describes Noé, talking about his motivation. Schulz adds: “The unique challenge was that we needed to apply all our knowledge from the bachelor's program from the different disciplines – and prepare for the mater's program as well”. Perhaps that is what makes lightweight construction so fascinating – the multidisciplinary approach is a challenge for young engineers, and success encourages them to dream big.

About the Pforzheim University of Applied Sciences – Technology department

The Pforzheim University of Applied Sciences has three departments – Design, Technology, and Economics and Law. The departments combine creativity with business training and technical precision. The Technology department at the Pforzheim University of Applied Sciences focuses on sustainable instruction and application. The department’s research areas of product development and production cover the two core processes of production and product development in a company. Since these processes are very closely connected in a company and influence one another, they have been combined into one focal area.