Magda Zydzik explains how 3D printing is aiding lightweighting efforts for drones
Over a century ago, the first unmanned aerial vehicle (UAV) – more commonly known as a drone – was brought to life with a paper mache and wooden fuselage and wings made from cardboard. Given their history, drones are by no means a new invention, but recent advancements in technology, such as lighter materials and improved flight controllers, have paved the way for greater adoption of drones in consumer and commercial markets. Initially viewed as a military device, drones now have a foothold in applications that demand high precision and cost-effectiveness compared to pre-existing methods. Applications include inspection, maintenance, surveillance, monitoring, precision agriculture, mapping and surveying, among others.
Looking at the horizon for drone technology advancements, a common theme is weight reduction. As drone applications push for higher payloads, longer flight times and reduced weight, composites have become the material of choice with their high strength to weight ratios. Composites manufacturing brings drone-prototyping materials a long way from the paper mache and cardboard initially used.
Furthermore, advancements in additive manufacturing (AM) have significantly shortened product life cycles and have expedited bringing new products to market. To date, the composites and AM industries have responded to the growing drone industry – the composites industry with stock shapes of varying fibre orientations and moduli, and the AM industry with 3D-printed tooling for conventional composites manufacturing, as well as chopped-fibre reinforced materials to replace unreinforced parts, among other examples.
Composites and additive manufacturing join forces in drone design
Arevo manufactures composite parts using robotics-based additive manufacturing. It believes that its combination of AM, continuous carbon fibre composites and software holds great promise for the drone industry. Using its Xplorator software and directed energy deposition (DED) printing process on its Aqua system, all of which are developed in-house, drone frames and other large, structural parts can be designed lighter and brought from concept to production.
Arevo was presented an opportunity to manufacture a structural frame for an inspection drone. The objectives were to achieve at least 40% weight reduction while maintaining structural integrity. The original design featured a motor-to-motor span of 850mm – well within the Aqua system’s 1,000mm x 1,000mm x 800mm (xyz) build volume – and required a 33.5mm vertical space in the centre compartment for ancillary parts. Finally, it was required that the new design support an 8kg payload and that original hole locations were preserved to accommodate for previously designed and sourced components.
Upon completing the design and manufacturing of the drone frame using Arevo technology, 50% weight reduction was achieved as compared to the original design (see Fig. 1).
Upon reviewing the original design from the customer, an initial structural finite element analysis (FEA) was performed on the customer’s design using the Xplorator software and representative material properties of carbon tubes from the original design as input.
Fig. 2 shows the extremum principal stresses and regions of stress concentration near the motor mount as well as on the top and bottom (not shown) of the drone. The lowest factor of safety (FOS) for the original design is approximately 1.5, validating that the original design would satisfy load requirements made with the originally intended manufacturing process and FOS.
The initial FEA results informed the design direction to reduce the stress concentrations in the X-shaped support region and integrate parts in the motor mount region of the original design (shown in Fig. 3). To improve the strength in this region, the X-shaped supports were replaced with a conical motor housing and were integrated with the boom and landing gear.
Next steps in the lightweight drone design
Once the software informed the design direction through the initial FEA, a final design was prepared. The additive finite element analysis (AFEA) module in Xplorator was used to validate the design’s strength, taking into account the anisotropic properties of Arevo’s composite filament used as feedstock for the Aqua system. The input for the AFEA module is material properties from extensive characterisation performed on coupons printed via DED on the Aqua system. Using the same 8kg payload load case, AFEA was conducted on the final design.
Further analysis (see Fig. 4) revealed a high FOS of 5 in most regions with the lowest FOS of 2.63 near the top surface. The high FOS suggests that the weight can be further reduced in select regions for future prototypes, with an initial conservative estimate of 10% further weight savings – 60% below the original design.
Upon structurally validating the design, the final toolpath and manufacturing blueprint, or GCODE, was prepared using the slicing module. Looking closely at a subsection of the sliced model, the continuous fibre path wraps from one side of the boom, around the motor housing and supports, and onto the other side of the boom to meet the rest of the chassis, therefore providing continuous fibre support around the perimeter of the chassis and booms of the final design.
Once the manufacturing blueprint was prepared, the part was manufactured on the AquaSystem. High tolerance holes were later machined via CNC.
In conclusion, 50% weight reduction of the original design was achieved and the structural requirements were met for the load case provided using Xplorator to inform and validate Arevo’s optimised design. The next step is to perform assembly and flight testing to inform future design and product improvements.
The drone case study showcases how this technology enables both virtual design iteration for additive manufacturing of composite parts and virtual validation before manufacturing to achieve lighter weight structures. Additionally, there is an opportunity for further weight reduction in select regions where the FOS is high. Finally, Arevo believes that this design can be further optimised to integrate the parts into one printed, structural frame.
Magda Zydzik works in applications development at Arevo