# 3D-Printed Bio-Inspired Mechanisms for Bird-like Morphing Drones
## 3 Results
### Manufacturing and Testing  
Reinforced balsa wood and interwoven fiber-glass composite laminate were considered for the feathers. Figure 8 shows sample manufactured feathers from both options. Due to its relative simplicity, reinforced balsa wood was selected for the proof-of-concept model. With 3D drawings of all feathers, a laser cutter created the wing and tail feather vanes from 3-mm thick Balsa wood sheets. Carbon-fiber rods of 1.5-mm diameter were used as feather shafts. A strong cyanoacrylate adhesive was applied to bond each shaft to its vane at three points to adjust its orientation. The feathers were then reinforced by a layer of vinyl tape with optimal bidirectional properties for this application. The balsa wood created a solid surface on which aerodynamic forces could act. Meanwhile, the vinyl tape provided reinforcement against bending forces across the wood grains while still keeping the feathers lightweight. The carbon fiber rods offered a lightweight and resilient means of suspending the feathers from their mounting points. The feathers were then inserted into their appropriate pins in the wing or tail subassemblies. Fiber-glass composite feathers, on the other hand, were made of one glass fiber ply taking the outer shape of the feather vane,  
Figure 7: Resultant displacement (**a**) and Von-Mises stress (**b**) distributions of the outer wing flexible corrugated structure. and a smaller strip acting as a second ply in central part of the feather. The carbon fiber feather shaft is sandwiched between the two plies, significantly reinforcing the central part of the feather, as shown in Figure 8b. The outer wing's flexible corrugated PCTPE section was 3D-printed, and short 1.5 mm carbon fiber rods were inserted in the holes of its web. Feather adaptors were connected to these rods from one side and the feather shafts from the other. Each adaptor had a different angle to allow the feathers to take the shape of the seagull's outer wing (Figure 9a). The servomotor was placed in its housing in the elbow hinge. The Corona DS-843 MG digital high torque micro servo (Torque: 4-4.8 kg.cm, speed 0.12-0.10 s/60\({}^{\circ}\), operating voltage: 4.8-6 V, weight: 8.5 g, dimensions: 23 \(\times\) 9 \(\times\) 23 mm) was used for all mechanisms. A carbon fiber rod was connected to the servomotor and ran along the outer wing above the feathers to a connector at the wing tip. The actuation of this servomotor causes wing feather contraction and expansion when the rod is pulled backward and forward, respectively. Actuation of the outer wing resulted in a 56.3\({}^{\circ}\) camber morphing angle, corresponding to 102 mm of tip vertical deflection (Figure 10a). For comparison, Figure 10b shows the deformed shape from the preliminary finite element analysis, presented in Section 3.1. The camber morphing angle from the simulation was 45\({}^{\circ}\), with 96.6 mm vertical tip deflection. Uncertainty of the material properties used in simulation, manufacturing imperfections, and the slight difference in the applied load's magnitude and direction are possible causes of the difference in the deformed shape between the two models. However, the servomotor, that was selected guided by the simulations, proved to be capable of properly deforming the model to the retracted configuration and support it via the carbon-fiber rod in its morphed configuration. The wing actuation test is presented in Video S1 in the Supplementary Materials. Figure 8: Sample manufactured feathers: (**a**) reinforced balsa wood, (**b**) interwoven fiber-glass composite. Figure 9: Proof-of-concept model of the proposed outer sweep-morphing feathered wing design: (**a**) expanded configuration, (**b**) tucked configuration. The inner wing skin with an S1223 airfoil profile was then wrapped around the inner wing structure to protect it and give the wing its desired aerodynamic profile. The skin was bonded to the fuselage once the final location of the wing was adjusted for stability. The covert layers were bonded to the top surface of the inner wing skin.