Flying Robots (MAV): Design & Application

The design and development of flying robots has been currently hindered by the lack of applicability of conventional aerodynamics equations/principles to the small size vehicles flying at extremely low Reynolds number. Also, conventional optimization techniques and algorithms have shown very limited success in these applications. Trial and error has been the most effective design tool in many cases often leading to computationally intensive and expensive design processes with longer iteration time. The non-availability of physics based analytical tools and the computational expense of numerical methods makes an empirical design optimization approach a practical alternative. This current paper has been based on Flying Robots (MAV) design & application.

Introduction

Unmanned aircraft systems (UASs) have drawn increasing attention recently, owing to advancements in related research, technology, and applications. While having been deployed successfully in military scenarios for decades, civil use cases have lately been tackled by the robotics research community. This paper overviews the core elements of this highly interdisciplinary field, the reader is guided through the design process of aerial robots for various applications starting with a qualitative characterization of different types of UAVs. Design and modeling are closely related, forming a typically iterative process of drafting and analyzing the related properties. Therefore, we overview aerodynamics and dynamics, as well as their application to fixed-wing, rotary-wing, and flapping-wing UAVs, including related analytical tools and practical guidelines. Respecting use-case-specific requirements and core autonomous robot demands, we finally provide guidelines to related system integration challenges.

MICRO AIR VEHICLE(MAV) or UNMANNED AIR VEHICLES

Micro Aerial Vehicle, is a class of UAVs that has a size restriction and may be autonomous. Modern craft can be as small as 15 centimeters. Development is driven by commercial, research, government, and military purposes; with insect-sized aircraft reportedly expected in the future. The small craft allows remote observation of hazardous environments inaccessible to ground vehicles.

Types of Flying(Aerial) Robots:

Compared to the categorization of manned aviation ,aerial robots classification is more complex, as the term currently refers to a very wide variety of systems of different scale, mechanical configuration, and actuation principles. In their vast majority, aerial robots correspond, in one way or another, to miniaturized versions of manned aircraft designs. Relatively classical fixed-wing unmanned aerial systems designs and rotary-wing unmanned aerial systems such as those shown in Fig are common vehicle configurations one may encounter in most applications, including those of surveillance, monitoring, inspection, mapping, or payload transportation. However, even within these relatively traditional concepts, several design aspects differ from those chosen for manned systems. This reflects the fact that for different scales, the variation of the physical properties behavior, along with the search for optimized designs, will naturally lead to modified and novel design considerations. Below are some of the aerial robots pictures :

Airplane Modeling and Design

Ever since the beginning of aviation, a broad spectrum of airplanes has been built and operated successfully: size, speed, and maneuverability vary widely and as a function of application. Since design and modeling are strongly related, we want to first give an overview of the physical principles common to all such configurations and provide analysis tools for characterizing static and dynamic properties of an airplane. The design problem somewhat constitutes the inverse problem for specified target characteristics, the engineer needs to find a suitable configuration; we therefore provide a summary of design guidelines aimed at fast convergence to a suitable design. Finally, a simple and classical autopilot scheme is presented underlining the need for models also at that stage.

Design Considerations for a small Micro Aerial Vehicle(MAV)

There is now a great interest in designing MAVs that are small with fixed or flapping wings. As the size of MAVs decrease, the amount of thrust and lift that can be generated by the wings will also decrease, limiting the weight and payload capacity of the MAV. For every small MAVs with fixed wing designs, it requires critical air velocities that limit the efficiency of the MAV. Thus, flapping wing designs can be more desirable, enabling the MAV to fly easily much like a rotorcraft structure. The rotorcraft structure is the more efficient one, since it contains of tentacles in its design, where each tentacle is fitted with the motor and produces the lift required. Here we briefly review the design of such MAVs which uses tentacles.

Components and Take-Off Weight

One advantage of MAV design over conventional full-scale aircraft design is that the calculation of take-off weight can be performed with relatively little use of empirical data. This is due to the fact that most of the components to be carried, as well as their size and weight, are known. The disadvantage, however, is that the vehicle must be designed such as to accommodate these components. Generally, the components consist of the a propulsion system, video camera and transmitter, radio control receiver and actuators, and batteries for the electronic components.

The propulsion system deserves the most attention as there are two distinct options: electric power or internal combustion engines. Although off-the-shelf (and affordable) battery technology is steadily improving, it is not yet at the stage where it can outperform an internal combustion engine in terms of thrust per unit weight (this is more due to a deficiency in battery technology rather than motor efficiency). Early on, the decision to use an internal combustion engine for propulsion was made due to the availability, low cost, and high thrust to weight ratio achievable with glow-fuel engines.

Propulsion System

The video transmitter and camera used are the smallest and lightest that could be found within the MAV, they have low weight and helps to lift off easily. The last item contributing to take-off weight is the structure of the MAV. The most effective way to obtain an estimate for structural mass is to approximate it based on the structures of other MAV. Average structural weight of similar MAV test models constructed since the beginning of the project was 150 grams. Indeed, this estimate was very close (usually within a few grams) of the actual structural weight of all vehicles built up to date.

Estimation of Cruise Velocity:

With the take-off mass defined, the next step in the design procedure is to determine the cruise speed of the MAV. This step is particularly difficult because, as mentioned earlier, there is no experimental data of the thrust of the engine selected versus airspeed. Without this information, the typical method of determining cruise speed (in which the cruise speed is the velocity at which the thrust of the engine equals the drag of the airplane) cannot be used. An approximation of the expected cruise speed must be made instead. Furthermore, it must be assumed that this speed will not vary much with the shape of the wing or the configuration of the airplane. Although this method may not yield exact solutions to be used for design, it will provide a way of comparing

Required Lift Coefficient

With the take-off weight and estimated airspeed known, it is possible to calculate the lift coefficient required to sustain level flight.

Selection of Wing Planform Shape

In order to determine which wing shape is best suited for a micro aerial vehicle, wind tunnel experimental data was used to develop an empirically-based design and analysis procedure. For wings of aspect ratio between 1 and 2, the coefficients of the quadratic polynomials were linearly interpolated. That is, for a wing of aspect ratio 1.5, for instance, the bAR=1.5 coefficient will be the average of the bAR=1 and bAR=2 coefficients, and so on. In addition, the angle of attack at which stall occurs was assumed to also vary linearly with AR.

The assumption that the coefficients of the quadratic functions and the stall angle of attack vary linearly with respect to aspect ratio has not been validated and is the focus of future research. The results obtained using this assumption do not necessarily give exact predictions of absolute lift and drag. They do, however, permit the direct comparison of different wing shapes. Also, they are expected to provide a reasonably good first estimate of the lift and drag forces for wings of AR between 1 and 2. For each value of the parameters of wing area and aspect ratio there exists an angle of attack at which a given wing shape achieves the required lift coefficient. As the aspect ratio increases, however, the required lift coefficient may exceed the wing’s maximum CL. When this happens, the wing stalls and there is no angle of attack at which the required CL can be achieved.

Selection of Aspect Ratio and Wing Area

Having determined that a shape similar to the inverse Zimmerman is the optimum, the next task was to size it: that is, to select the aspect ratio and wing area. As was discussed earlier, this step is difficult to do accurately due to the uncertainty of the estimated airspeed, the assumptions used in the generation of the interpolation model, and the fact that a thin wing with zero camber will have different lift and drag characteristics than a ready-to-fly MAV with a fuselage and wings with camber and thickness. The presence of these new variables will likely change the absolute aerodynamic performance but is unlikely to change the difference in performance between wings of various shapes.

Rotorcraft Micro Aerial Vehicle

Various types of rotorcraft MAV configurations have been developed in the past (some examples are shown in Fig below), from helicopter-type MAVs such as Drones over a vast selection of multicopter configurations such as tail-sitter vehicles such as are completely new types of flight mechanisms. The design, modeling, and system analysis process for all these RW-MAV types is essentially very similar and is largely based on the methodologies originally developed within the aerospace community for full-scale rotorcraft design and evaluation. In this context, it is important to realize that the rotorcraft design process goes beyond mere efficiency and payload considerations focused on the propulsion components (e.g., using BEMT). Designing an effective RW-MAV should in principle also include flight dynamics assessments of the entire robotic flight platform.

Design

Here we see a developmental stage of multi-tentacle MAV platform. It is based on a four rotary wing aerial platform such as quadrotor system and three of four DOF (degree of freedom) tentacles attached to the bottom of it. Unlikely mobile manipulating research which focuses more on stability and control of manipulators and floating platform a multitentacle system suggests a new paradigm of mall ale aerial robotics. Newly integrated and developed multitentacle aerial vehicle can have extended loco motions compared currently existing flying only vehicles such as vertically and upside-down perching capability.