CONCEPTUAL DEVELOPMENT AND DESIGN OF THE FWMAV 1 Conceptual Design Decision

Developing an Efficient Bioinspired Flapping Wing Micro Aerial Vehicle for Research

3. CONCEPTUAL DEVELOPMENT AND DESIGN OF THE FWMAV 1 Conceptual Design Decision

An analysis of the existing FWMAV projects was carried out to compare systems and find the best suited structure for the project. Referring to the conceptual development of the FWMAV, the following conclusions and corresponding decisions of this analysis were made, with regard to the wings and tail.

The wing configuration selected for the FWMAV is a biplane “X” configuration, similar to TU Delftʼs and Berkeleyʼs FWMAV. This is justified as follows: the biplane configuration allows for wings with only active degree of freedom (DOF), hereby simplifying the design process and, most importantly, reducing the weight. Furthermore, this configuration benefits from the advantages of the clap-and-fling effects which, as mentioned before, have shown to augment total aerodynamic lift generation. In terms of tail configuration, the choice made for the tail is a standard inverted T- tail, as it is the simplest of designs, and is therefore the design choice for the first prototypes.

Additionally, the standard tail is also the lightest configuration, requiring only two servos and light surfaces. A great importance is placed on the weight of the first prototypes, given that the priority is to have a flight capable system, which should have a sufficient weight margin for an extra payload. The structural design explained above is illustrated in Figure 3.

Figure 2-Clap-and-fling motion by position. The black lines and arrows represent the flow of air, while the circulatory lines indicate the presence and direction of vortices (Caetano, 2016)

Figure 2- Clap-and-fling motion by position. The black lines and arrows represent the flow of air, while the circulatory lines indicate the presence and direction of vortices (Caetano, 2016)

A similar configuration called clap-and-peel is used for flexible wings and brings a number of advantages.

During the peel, the flexible wings inertia and suction reduce their AOA, hereby reducing drag, and also promoting an increase in the LEVs (Caetano, 2016). Additionally, this configuration is found to reduce the formation of the starting vortex, which is justified by the influence of the circulation in the opposing wing (Sane, 2003). As such, reducing the intensity of the starting vortex will ease the establishment of the Kutta condition, resulting in faster lift force generation. This configuration has proven, in insects, to result in up to 25% more aerodynamic lift, compared to conventional flapping wing motions (Marden, 1987).

3. CONCEPTUAL DEVELOPMENT AND DESIGN OF THE FWMAV

3.1 Conceptual Design Decision

best suited structure for the project. Referring to the conceptual development of the FWMAV, the following conclusions and corresponding decisions of this analysis were made, with regard to the wings and tail.

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Developing an Efficient Bioinspired Flapping Wing Micro Aerial Vehicle for Research

weight. Furthermore, this configuration benefits from the advantages of the clap-and-fling effects which, as mentioned before, have shown to augment total aerodynamic lift generation. In terms of tail configuration, the choice made for the tail is a standard inverted T-tail, as it is the simplest of designs, and is therefore the design choice for the first prototypes. Additionally, the standard tail is also the lightest configuration, requiring only two servos and light surfaces. A great importance is placed on the weight of the first prototypes, given that the priority is to have a flight capable system, which should have a sufficient weight margin for an extra payload. The structural design explained above is illustrated in Figure 3.

6 3.2 Detailed Design Decision

This section aims to elaborate the final decisions that will incorporate the project, specifically regarding the following: flapping mechanism; wings; tail. In the search for a flapping mechanism, existing solutions were studied, since the design and creation of a mechanism would be far too demanding both time wise and financially. A study by Bruggeman (2010) on the DelFly II and its flapping mechanism (Figure 4a) proves as a valuable solution and has the advantage of having its detailed information available to the public.

As a means of comparison, Berkeleyʼs H^ Bird uses a similar mechanism, hereby proving the value of this solution, which is also compatible with the intended biplane “X” configuration.

However, this mechanism was produced according to particular specifications (Delft University of Technology, 2017) and, as such, is not commercially available. Nonetheless a commercially available solution was found by Micronwings (Micronwings, 2017) and fulfilled all the requirements (Figure 4b).

Consequently, the solution found is composed of a wing with a 1 mm thick main rod, an aspect ratio of 1.75 and the dimensions displayed in Figure 5a. Regarding the stiffeners, their thickness should be around 0.28 mm, and their placement as displayed according to Figure 5a. The reasons for these choices are, this design has been studied experimentally by a detailed scientific work, which intended on its optimization. Comparatively, another research possibility, Berkeleyʼs MAV wing, stems from a commercial product with no modifications made to the wings. Thereafter, allowing for future adaptation to the motorʼs output force, three different wing proportions were designed: wing 140, 119 and 98, after their main rod length.

Figure 4-a) DelFly II flapping mechanism; b) Flapping mechanism acquired from Micronwings Figure 3-Conceptual representation of the chosen design structure for the FWMAV

Figure 3- Conceptual representation of the chosen design structure for the FWMAV

As a means of comparison, Berkeleyʼs H Bird uses a similar mechanism, hereby proving the value of this solution, which is also compatible with the intended biplane “X” configuration. However, this mechanism was produced according to particular specifications (Delft University of Technology, 2017) and, as such, is not commercially available. Nonetheless a commercially available solution was found by Micronwings (Micronwings, 2017) and fulfilled all the requirements (Figure 4b).

6 3.2 Detailed Design Decision

As a means of comparison, Berkeleyʼs H^ Bird uses a similar mechanism, hereby proving the value of this solution, which is also compatible with the intended biplane “X” configuration.

Figure 4-a) DelFly II flapping mechanism; b) Flapping mechanism acquired from Micronwings Figure 3-Conceptual representation of the chosen design structure for the FWMAV

Figure 4- a) DelFly II flapping mechanism; b) Flapping mechanism acquired from Micronwings

Following, the type of wing to design was determined, to this extent existing wing designs and corresponding publications were researched, e.g. Bruggeman (2010), being the following choice for the wing design an adaptation that incorporates the most beneficial parameters. Consequently, the solution found is composed of a wing with a 1 mm thick main rod, an aspect ratio of 1.75 and the dimensions displayed in Figure 5a. Regarding the stiffeners, their thickness should be around 0.28 mm, and their placement as displayed according to Figure 5a. The reasons for these choices are, this design has been studied experimentally by a detailed scientific work, which intended on its optimization. Comparatively, another research possibility, Berkeleyʼs MAV wing, stems from a commercial product with no modifications made to the wings. Thereafter, allowing for future adaptation to the motorʼs output force, three different wing proportions were designed:

wing 140, 119 and 98, after their main rod length.

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Following, the decision on the shape of the horizontal stabilizer was conducted and the solution of an elliptical design for the leading edge of the stabilizer, was chosen. Afterwards, the maximum chord length had to be decided for the horizontal stabilizer. As the intention was to build an elliptical shape, the value adapted was 55 mm, in comparison, 67 mm would make the structure of the horizontal stabilizer circular in shape. Thereafter, the vertical stabilizer was designed with the intent to make a proportional tail. The total height of the tail was designed to be half of the horizontal length, of 135 mm, therefore the final value of 67 mm was selected. The last step was to decide on the length of the moving surfaces, the decision was approximately one quarter of the total length of the stabilizing surfaces. This proportion was chosen due to the low speeds at which the surfaces would have to be effective, resulting in a length of 20 mm for the moving surfaces. After adapting all these specifications in SolidWorks 2016, the final design is represented in Figure 5b, which was used for the construction of the first prototypes.

Regarding the selected inverted T-tail design, the decision made was to assemble a similar tail design to the ones found in existing FWMAVs. In order to achieve this, research started from one of the few publications found with specific tail dimensions (Caetano, 2016, p. 27). The main dimension adapted was the trailing edge length of the horizontal stabilizer, of 134 mm. Given that the wing area would be approximately the same, this comparison would be suitable for the FWMAV in development. Following, the decision on the shape of the horizontal stabilizer was conducted and the solution of an elliptical design for the leading edge of the stabilizer, was chosen. Afterwards, the maximum chord length had to be decided for the horizontal stabilizer. As the intention was to build an elliptical shape, the value adapted was 55 mm, in comparison, 67 mm would make the structure of the horizontal stabilizer circular in shape. Thereafter, the vertical stabilizer was designed with the intent to make a proportional tail. The total height of the tail was designed to be half of the horizontal length, of 135 mm, therefore the final value of 67 mm was selected. The last step was to decide on the length of the moving surfaces, the decision was approximately one quarter of the total length of the stabilizing surfaces. This proportion was chosen due to the low speeds at which the surfaces would have to be effective, resulting in a length of 20 mm for the moving surfaces. After adapting all these specifications in SolidWorks 2016, the final design is represented in Figure 5b, which was used for the construction of the first prototypes.

3.3 Electronic Hardware

Lastly, the control system corresponds to the assembly of an electronics system which allows for remote control of the FWMAV, and is composed of the following components: receiver;

actuator; motor; battery. From the selection of electronic solutions researched, the following were selected for the construction of the project. The receiver used was DelTangʼs RX31d, which displayed two brushed electronic speed controllers, four actuator outputs, was compatible with 2.4 GHz frequency and weighed 0.24 grams. With regard to the control components, from the three acquired solutions, two electromagnetic actuators, weighing 0.35 grams and 0.68 grams,

Figure 5- Proposed design and dimensions: a) 140 wing; b) tail

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Figure 5- Proposed design and dimensions: a) 140 wing; b) tail

3.3 Electronic Hardware

Lastly, the control system corresponds to the assembly of an electronics system which allows for remote control of the FWMAV, and is composed of the following components: receiver; actuator;

motor; battery. From the selection of electronic solutions researched, the following were selected for the construction of the project. The receiver used was DelTangʼs RX31d, which displayed two brushed electronic speed controllers, four actuator outputs, was compatible with 2.4 GHz frequency and weighed 0.24 grams. With regard to the control components, from the three acquired solutions, two electromagnetic actuators, weighing 0.35 grams and 0.68 grams, and a mechanical actuator (1.5 grams) were acquired. The best compromise found, between weight and force generation, was the 0.68 grams magnetic actuator. The motor acquired was a 6 mm brushed motor, compatible with the receiver and the flapping mechanism acquired, which presented a valuable solution in comparison to brushless motors researched. Lastly, the batteries acquired were lithium-ion with a 3.7V output and three different capacities: 100 mAh; 150 mAh; 180 mAh. As seen further, the two batteries with the highest capacity were too heavy for flight.

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4. DESIGN IMPROVEMENTS

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