Design and Analysis of Quad Copter Chassis Using Shape Optimization Technique

Abstract

Unmanned aerial vehicles (UAVs) are replacing many traditional methods ranging from simple play toys to critical defense operations. UAVs or drones that are the little flying machines are used in space, defense, food delivery, pest sprays for agriculture, consumer goods delivery, land-surveillance and the list goes on. However, the physics behind it demands a lesser weight for drone to fly high as lesser the weight, lesser is the power required to operate. In all the components that make up a drone, is the frame that is most important structure which holds and bears everything at place. So the material used for the drone frame plays a very crucial role for it should have a lesser mass but sufficient strength. In this work, frame is modeled taking into consideration, its sturdiness and stress analysis is conducted using Autodesk Fusion 360 software and compared for different materials of frames from plastics to metals and the design is shape optimized to meet the objective.

Introduction

I. INTRODUCTION

A drone is a flying machine which is a pilotless aircraft formally known as UAV. Since it does not need a human pilot and taking the advantage of sizing the UAV as per the requirement, the application areas are far very wide for a UAV. They are used in agriculture, monitoring, transportation, goods delivery agent, land-surveillance, inspection [1] only to name a few. To be able to fly, drones must be able to generate upward thrust to overcome their own weight. This makes drone a weight critical object where any additional gram on the flying machine will turn out to be costly. Another important aspect that cannot be overlooked is the need to cut down material utilization to as much as possible. Material depletion rates are alarming and so are the pollution rates, which demands to lessen material wastage and landfill. On the design side of a drone, higher the material, higher is the weight. Higher the weight, higher will be the power consumption. So a design that can cut down material without affecting the strength and mechanical properties is a great opportunity to overcome all the limitations that come from a larger mass [2]. Every gram that is lessened can improve the performance of drone like increased payload carrying capacity, extended flight times, better maneuverability, less material consumption, low power consumption, less wastage that means less pollution and landfill, and more economical.

A. Quad copter frame

Frame is the structure of drone. It holds and bears everything at place acting as a skeleton to fit in all the components of drone. The size of the frame is measured as the diagonal distance between motors. If this dimension is less than 150mm, the size is categorized under micro, otherwise it is considered as a mini. Depending on the no. of motors, drones are named as tri-copter, quad-copter, hex-copter, etc. of which quad-copter is the most popular design for the following reasons: mechanical simplicity, quantity of motors and Electronic Speed Controllers (ESCs) required for flight and their compact size.

II. PROBLEM STATEMENT

In this work, frame is chosen as weight critical component. Unibody design will be stiffer and stronger, hence as unibody quad-copter is considered in this work for which shape optimization of frame is carried out to attain a low mass structure without affecting the strength [3].

Since weight is directly proportional to cost, that includes the flight times, range, material depletion, material wastage, pollution are a few that makes up to total cost of a heavy weight object, shape optimization tool is utilized to reduce the weight of the component. Shape optimization technique is applied to drone frame to reduce the mass of the frame without affecting the strength, sturdiness and stiffness of the frame.

III. OBJECTIVE

1. To design simple multi-functional frame for higher payload capacities (about 2.14 kg)
2. To make a simple but aesthetically appealing design
3. To make a low weight component
4. To make a good strength frame
5. Should be economical

IV. GENERAL DESIGN AND ANALYSIS OF QUAD COPTER FRAME

A. Basic Design of Quad Copter Frame

The quad copter frame is designed to hold all the components in place. Design is carried out as per the figures 1 and 2 shown below. Frame size is 210 mm for a 4 to 5 inch propeller which is the diagonal distance from motor to motor. Each motor is positioned at right angle to adjacent motor to ensure stability and equal weight and thrust distribution [4, 5]. Three most popular materials used for drone frame are selected viz., Aluminium [6, 7], Al A356 T6 [8] and ABS plastic [9,10] keeping in mind their mechanical properties like strength, rigidity (as shown in table 1), weight, cost and availability.

The ultimate factor of safety (FOS) used in aircraft can be about 1.5. In general, an FOS of 2 is considered as a standard for tested structures and 3 for untested structures. The most important thing in aircraft application is it should have the lowest weight possible [2]. The FOS based on yield strength of materials is 15 for Al as well as Al A356 T6 whereas for ABS plastic it is 4.303. Amongst other factors, it is mainly weight that has its impact on the FOS and the least weight is with ABS plastic as it is only 39.26% of the weight of Al and 39.7% of the weight of Al A356 T6. So, ABS plastic is chosen for further analysis such that the strength is not compromise while further reducing the weight of the frame using shape optimization technique.

V. SHAPE OPTIMIZATION AND STRESS ANALYSIS OF QUAD COPTER FRAME MADE OF ABS PLASTIC

A. Shape Optimization of Quad Copter Frame (Iteration 1)

Fusion 360 software is used to shape optimize the basic model of quad copter frame designed to bring out the best of the design. The following is the 1st iteration of the design to cut down mass and material. The 1st iteration is the basic model of the quad copter frame on which the boundary conditions and loads are applied as discussed in section 4.2.  Shape optimization or otherwise topology optimization is applied to find the regions in the design component that does not contribute much to load or otherwise whose absence does not affect the strength, stiffness or rigidity of the component [17 to 23].

B. Analysis of Shape Optimized Quad Copter Frame

On simulating for optimizing shape of the basic model, the target is set to reduce mass by at least 30%. This is done by modifying the design in every iteration such that the design still meets the strength criteria. The 1st iteration is worked out on the basic model (fig 2), and the stress distribution is studied (Fig 11). The blue color region in fig. 11 shows that the region has negligible stress and that region is not contributing much in carrying the load and hence can be reduced. The basic model is redesigned keeping in mind the stress distribution and fig. 12 is the outcome whose weight came down to 76.75g.

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References

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Copyright

Copyright © 2023 Srawanee Sreeramoju, M. Sreenivasa Rao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.