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ScienceDirectProcedia Engineering 00 (2014) 000–000

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“APISAT2014”, 2014 Asia-Pacific International Symposium on Aerospace Technology, APISAT2014

Design and Performance Analysis of an Electromagnetic Tricycle Operated in an Airport

Puttaratorn Ekapun*, Toh Yen Pang School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Bundoora, Melbourne, VIC 3083, Australia

Abstract

This paper presents a new body design of modern electromagnetic tricycle for traveling in an airport with zero emissions. The design of the tricycle’s electromagnetic wheels utilised the theory of automotive dynamics and a brushless DC motor. These consisted of two sliding rings, which are electromagnet and have a permanent magnet inside the wheels. Furthermore, a design chassis was developed using ABAQUS with its dynamic analysis based on the chassis of an existing golf cart model. The chassis was designed and analysed for energy absorption to reduce impact force and protect passengers. A 3D printing prototype was produced to represent the conceptual design realistically, and to validate the functionality of the final design on a small scale.© 2014 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA).

Keywords: Electromagnetic wheel, finite element analysis, structural behaviour, ABAQUS, FEM, future car, CATIA

1. Introduction

This research project aimed to design an innovative electromagnetic car that can provide transport facilities for two passengers travelling around an airport. The conceptual design began with three independent electromagnetic wheels without drive-train systems in order to reduce the energy loss. Electromagnetic theory was used to determine the performance of the electromagnetic wheels.

Besides electromagnetic theory, the propulsion and structure of the electromagnetic tricycle (EMT) were two design criteria also considered. In terms of the propulsion system, the EMT was designed to drive on a flat road and climbing hill (40 percent slope) at a maximum velocity of 60 kilometres per hour (km/h) and acceleration from zero

* * Corresponding author. Tel.: +66-864128761;.E-mail address: s3396086@student.rmit.edu.au

1877-7058 © 2014 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA).

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to maximum speed within twelve seconds. The chassis was the main structure that supports the vehicle weight and absorbs impact energy in a crash event.

2. .Methodology

The design methodology consisted of two main parts: (I) theoretical calculation; and (II) design optimisation. The theoretical calculation process was started with an automotive dynamic calculation in order to determine the minimum required drive force. Then, the electromagnetic calculation and optimisation were carried out to determine the performance of the electromagnetic wheel and to select the optimal design (purple line in Figure 1). The design process included the chassis and exterior designs. The chassis design started with the modelling of four chassis concepts in the first stage. The chassis was tested in both static and dynamic analyses using ABAQUS software. The results were represented in terms of force-displacement and energy graphs. The best two chassis were selected and then subdivided into four new chassis. These new chassis were not only tested by the same method as the first stage, but also optimised by considering different types of material in order to choose the best shape of the chassis with the appropriate material. The exterior design started with hand sketches. The designs were then modelled by computer using CATIA software. A survey of thirty people recruited through social network was used to select the preferred shape of EMT. After completed all above process, the final concept and prototype were produced to check how the model could work in reality.

Fig. 1. Flowchart of design and optimisation process

3. Theoretical calculation

The theoretical calculation consisted of two major tasks: (I) basic automotive dynamic; and (II) electromagnetism as presented in Figure 1. The results are presented in terms of performance data and size specifications. In order to select the optimal design, the optimisation parameters utilised three main factors, which were torque-speed graph, acceleration, and power-speed graph. The optimisation step began by setting a concept A (width equal 100mm) as initial wheel width. After completing the calculation in both automotive dynamic and electromagnetic, if the result did not achieve the objective requirement, then the optimisation loop started by increasing size of wheel width.

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3.1 Basic of automotive dynamic calculation

The tractive effort was first calculated. Tractive effect was a summation of four major resistance forces: rolling fiction; aerodynamic drag; hill climb force; and the force required for linear acceleration [2]. Then, the efficiency and drive forces for each wheel were calculated [2]. In order to protect the motor from overload damage, torque must be considered with a service factor. A service factor of 1.15 was applied [3], which resulted in a torque of 423.29 N.m for each wheel.

3.2 Electromagnetic calculation

The amount of torque depended on angular velocity. A basic theory of DC motors explains that the level of torque declines with increasing speed as shown in equation (1):

(1)

where Km = constant, = total magnetic flux, E⦶ s = battery voltage, Ra = amateur resistance (Ra), and ω = angular velocity. Km, the motor constant, was a key factor that determined the performance characteristic of the motor. The motor constant was determined by the number of turns (n), radius of the shaft (r), flux density (B), width of the wheel (l), and electric current (I), as in equation (2) [1]

(2)

The number of magnetic poles equals torque divided by total flux and electric current. The outcome was 5.497 pairs, but the number must be an integer. Thus, the number of magnetic poles became six pairs. The angular velocity was determined using equation (3), where: E = electric voltage and ω = angular velocity in round per minute (rpm).

(3)

After completion of the above calculation, the results were present in terms of torque-speed graph as displayed in Figure 2(a). However, the efficiency of the motor changed after the angular velocity reached a critical speed (ωc). The function between maximum torque and significant speed was shown in equation (4). In the case of constant torque, the speed was calculated using angular speed (ωc), gear ratio (G), and radius of the shaft (r) [2].

(4)

The numerical of acceleration model utilised the equation (6), where rolling friction (μrr), coefficient drag (Cd), velocity (ν), and gear efficiency (ηg) [2]

(5)

where μrr = rolling friction, Cd = coefficient drag, ν = velocity, and ηg = gear efficiency [2]. After obtaining the solution for the differential equation, MATLAB was employed in order to plot the acceleration of EMT by arranging velocity on the y-axis and time on the x-axis. Figure 2 represents three major tools of the optimisation process: torque-speed graph; acceleration model; and power-speed graph.

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Fig. 2. (a) Torque-Speed graph; (b) Acceleration model (b) Power-Speed graph.

Table 1. Comparison concepts.

Achievable Concept A Concept B Concept C Concept D Concept E Concept F

Torque-Speed Unachievable Unachievable Achievable Achievable Achievable Achievable

Acceleration Unachievable Unachievable Unachievable Achievable Achievable Achievable

Power consumption rank First Second Third Fourth Fifth Sixth

Figure 2(a) shows the requirement of torque at 314.5 N.m (minimum drive torque with electric current equal 250 A at zero angular speed). Figure 2(b) presents the acceleration for each concept, except concept A because it took more than 45 seconds to increase speed from zero to 60km/h. The red dash-line shows the required acceleration. The power consumption was a function of torque and speed, and it performed in terms of the power-speed graph as it appears in Figure 2(c). According to Table 1, concept A, B, and C did not achieve the required condition in terms of torque and acceleration. Thus, concept D, E, and F were ranked in terms of power-speed in order to select the concept that consumed the lowest power. Finally, the concept D (wheel width equal 370 mm) was selected as the optimum design.

The concept D design was then coupled with the electromagnetic wheel, which used the 48 voltage batteries with 250 A of 30 cells Lithium LiFePO4 battery. The battery ampere-hour ratings were equal 400. The desired travel range was 142.9 kilometres, and the battery pack weight was 213.64 kg [4]. The amount of battery weight was applied to the total automotive weight calculation, which consisted of mechanical weight, weight of the structure, weight of drive-train system, equipment weight, battery weight, and useful weight. The result of the weight calculation demonstrated that the useful weight was 230.75 kg.

4. Chassis design

Chassis configuration was required to achieve acceptable strength to carry the total automotive weight and absorb impact energy in a crash. All frames structure were analysed in both static and dynamic tests using ABAQUS. The optimisation process for static and dynamic analysis used four different materials to compare their structural and impact performances.

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4.1 Static Analysis

Fig. 3. Existing chassis were modelled by ABAQUS

Figure 3 shows the shape and design of four different chassis. The static tests were conducted using ABAQUS to determine if the vehicle frame could support a total weight of all vehicle components and two passengers. The chassis was constrained at the centre of mass, and the total weight of EMT (785 kilograms) was applied at the centre of gravity to four of the existing chassis. The wheel was rotated in the same direction as the wheel would turn in reality.

4.2 Dynamic analysis

The process began with first four existing designs with the same controlled variables (speed, material of an impacted wall and boundary condition). Each concept was analysed using four different materials (A-36 steel, AL-5182, Al-6061, and C-6300). The impact velocity was set at 30 km/h (impact at a discrete rigid wall with a time step equal 0.01) because the airport regulations do not allow a person to drive a vehicle exceeding 25 km/h in the corridor area [6].

Fig. 4. First and second stage of chassis design

From the first stage of analysis, the first and second concepts were found to achieve a satisfactory level. Hence, the new design in the second stage was created based on the design flowchart as shown in Figure 4.

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5. Exterior design

The design and shape of EMT were created using CATIA software by Dassault Systems. The design concept was inspired by a whale shark and was called “RHIN ” (Figure 5), which has a large width at the frontal area and tapering width at the rear section.

Fig. 5. (a) Hand sketching of RHIN concept; (b) CATIA modelling of RHIN concept.

6. Results and discussion

Here we explain solutions in relation to the electromagnetic calculation, the result of impacted chassis, and the prototype simulation.

6.1 Electromagnetic Wheels performance

The aim of the project was to design the electromagnetic wheel, chassis and body in order to achieve optimal performance in terms of weight, power, durability and operating range of the EMT. The optimal electromagnetic wheels were found to be 370 millimetre in width with six pairs of magnetic coils. The design was not only able to achieve the required torque and acceleration, but also consumed power at the lowest level. Table 2 shows a comparison performance between RHIN concept and existing average specifications from four golf carts used in the airport. The efficiency of the electromagnet wheels was greater than existing golf carts except in relation to the useful weight. In order to enhance the performance, the current design used 30 cells of LiFePO4 battery that have significantly reduced weight capability.

Table 2. Comparison performance between RHIN concept and existing airport golf cart.

Performance parameters RHIN concept General airport golf cart

Travel range (km) 142.89 87.5

Power usage (kwh) 1.2 1.32

Useful weight (kg) 230.75 275

Full charging cost ($/hr) 0.12 0.132

Maximum speed (km/hr) 60 22.25

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6.2 Chassis design

In chassis design, the static analysis was only focused on the yield strength of the structure. If the stress level stayed below the yield stress, the structure was considered able to support the load. The result shows that all chassis achieved the acceptable static strength as presented in Tables 3 and 4. Furthermore, Table 4 also presents stress on second stage chassis with different materials to ensure that all the new designs had acceptable strength.

Table 3. ABAQUS static result for the first stage design.

Table 4. ABAQUS static result for the second stage design.

where , AL51 = Aluminium 5182 series, AL60 = Aluminium 6061 series , C63 = Nickel Aluminium Bronze 6300 series

The main purpose of the chassis is not only to support the vehicle components and body, but also to absorb the impact energy in order to reduce damage to the structure and protect passengers [8]. Figure 6(a) presents the ideal graph of force and displacement for brittle, medium toughness, and ductile materials [8]. The effective design requires the chassis to have the characteristics of ductile material.

Fig. 6. (a) Ideal force-displacement graph [5]; (b) Result of dynamic analysis with first four chassis.

The force magnitude of Concept 4 (Figure 6 (b)) was significantly higher within a short impact duration. In contrast, the force magnitude of the Concept 2 was constant after the impact because the chassis absorbed the crash energy, and this was followed by plastic deformation. This characteristic is suitable for chassis design. Therefore, the first and second concepts were used in the next stage of design.

In the second stage of the chassis design, each new concept used for different types of material (Aluminium 5182 series, Aluminium 6061 series, and Nickel Aluminium Bronze 6300 series). The best material for each chassis was selected and together these were combined to make a comparison and choose the optimum design. The result shows

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that the material that suited chassis 1.1, 1.2, 2.1, and 2.2 were Al-6061, Al-5182, C-6300, and AL-6061, respectively. Figure 8 represents a combination of chassis design and appropriate materials.

Fig. 7. Comparison impact properties between four selected chassis

As shown in Figure 7, chassis 1.2, which made from Aluminium AL-5182, had an extremely high level of reaction force, because it was made from an H-section beam that resists compression force. Thus, a large amount of impact force on the chassis was transferred back to the wall. There was also a prominent deformation in chassis 2.2 (Aluminium AL-6061), which meant the impact energy was transformed into plastic deformation. Thus, this chassis was the most suitable because it was not only strong enough to support the whole structure in a static case, but also minimised the impact force by absorbing most of the impact energy (low impact force and large displacement). In the further research, the chassis analysis had to include the torsion and bending analysis to obtain more realistic results.

6.3 Prototype and simulation

The prototype was produced to represent a realistic conceptual design, and to validate the functionality of the final design on a small scale. A radio control system was used to control the movement and mechanism of the prototype from a distance. The radio control was powered by 2200 mAh rechargeable Li-Po battery. The actual size of the prototype was scaled down and printed using a “Makerbot Replicator 2” 3D model printer with ABS (Acrylonitrile Butadiene Styrene) material. The controlled systems and moving speed of the wheel of the prototype were tested on the flat as well as climbing a sloping road (25.72 degrees). Figure 8(a) and 8(b) present the complete assembly of the printed prototype as tested in the real environment. The prototype can gain speed with high acceleration until it achieves critical speed. However, the exterior design could be further investigated using computational fluid dynamic modelling in order to optimise the aerodynamic shape in the future.

Fig. 8. (a) Prototype in CAD modelling and Assemble prototype; (b) Prototype was tested on flat road and inclination route.

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7. Conclusion

In this research, the theoretical calculation and design optimisation were considered for the EMT. The theoretical calculation focused on performance and size specification of electromagnetic wheels. The design achieved the requirements in terms of passenger capacity (2 passengers), torque (more than 314.5 N.m), speed (60 km/h), acceleration (0-60 km/h in 12 s), and low power consumption. Furthermore, the efficiency of this concept was greater than existing airport golf carts in terms of operation range, power consumption, and operating cost. In terms of chassis design, the most suitable material characteristic for the automotive frame was ductile material. The chassis 2.2 with AL-6061 was chosen as the optimal chassis design. The frame was not only strong enough to carry the whole structure weight but also able to absorb most of the impact energy. In modelling and simulation tasks, the prototype confirmed the mechanic capacity and the potential of the electromagnetic wheel. In relation to constant torque and gear-less propulsion, the prototype was able to increase velocity from zero speed rapidly until it reached its critical stage. The design of the wheel could be further improved by using electromagnetic analysis software that can the chassis analysis to obtain a more accurate result. The exterior design could employ computational fluid dynamics in order to optimise the aerodynamic shape.

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