Figure 2a illustrates the schematics of the flapping mechanism

  • Download figure
  • Open in new tab
  • Download PowerPoint

3.1. Flapping mechanism

A flapping mechanism based on a combination of four-bar linkage and pulley–string mechanism was designed for high flapping amplitudes to mimic the wing motion of the rhinoceros beetle. The rotary motion of the crank O1O2 is converted to the flapping motion of the linkage O2O3 through the couplers O1O2, which are rigidly glued to the large pulley. A small pulley is connected to the large pulley through a string to amplify the flapping motion (?) of the linkage O2O3 to a larger flapping motion of the output link (?), which is glued to the small pulley. An end of the leading edge of the wing is connected to the output link to create the flapping motion. The connecting string between the large pulley and small pulley at one side is twisted to create the flapping motions of two small pulleys moving in the same direction to create flapping-wing motions in the two wings. Figure 2b defines the maximum and minimum values of the sweeping angle ?, whose magnitudes are identical. When the O0O3, O2O3, ?max and ?min are predetermined as input parameters of the design, the length of linkages can be expressed as follows:

Figure 2. (a) Schematic of the flapping mechanism, (b) definition of maximum and minimum values of angle ? (?min = ??max) and (c) the fabricated flapping mechanism without wings.

  • Download figure
  • Open in new tab
  • Download PowerPoint

The relationship between the flapping angle ? of the small pulley and the flapping angle ? of the large https://hookupdate.net/nl/once-overzicht/ pulley can be determined as follows:

Carbon/epoxy panels with a thickness of 0.8 mm were used to fabricate all linkages and supporting frames. The parts were built with a CAD design software by using a CNC machine (MM-300S, resolution 10 µm, MANIX, Korea), and then manually assembled as shown in figure 2c. A reduction gear ratio of 21 : 1 was selected in the flapping mechanism to amplify the output torque from a DC motor.

3.2. Wing design and wing kinematics

The wing was composed of veins made of carbon strips and thin membranes made of polyethylene terephthalate. The wingspan from the wing root to the tip (R) was approximately 70 mm and the wing mean chord ( c ? ) was approximately 25 mm. The leading edges of the wings made of carbon rod with a diameter of 1.2 mm were attached to the output links of the flapping mechanism, while the wing roots were connected to the trailing edge connector, as shown in figure 3. The wing membrane was designed to freely rotate around the carbon rod at the leading edge. With this configuration, the flapping-wing system could produce the passive spanwise twist and chordwise camber during the flapping motion. More details can be found in Phan et al. .

Figure 3. Wing configuration used to create wing twist and camber. The wing membranes are freely rotated about the leading edges, while the wing roots at the trailing edges are clamped to the wing root connector.

  • Download figure
  • Open in new tab
  • Download PowerPoint

Details on the measurements of the wing kinematics can be found in previous studies [45,47] as this study only provides a brief summary of the measurement process. White dots were marked on the wing along seven wing chords located at 12.5%R, 25%R, 37.5%R, 50%R, 62.5%R, 75%R and 87.5%R, as shown in figure 3. Three high-speed cameras synchronized at 2000 fps with a resolution of 1024 ? 1024 pixels were used to track the locations of the marked dots on the wing during the flapping motion. Then, the three-dimensional coordinates of the marked dots were determined by analysing the sequential images obtained from the high-speed cameras by using the direct linear transformation method developed in a Matlab code .