BUILDING AN RC CAR – BRINGING TOGETHER ELECTORNICS AND FLUID MECHANICS

Project Overview

We are going to be constructing a high-speed RC car with the aim of optimising the body car shape to maximise its speed. This will be achieved by completing fluid simulations in Fusion 360 to optimise the aerodynamics on the shell. To manufacture the shell, we will employ FDM 3D printing in a range of materials. Furthermore, we will utilise our school’s CNC machine to experiment in other materials such as polycarbonate, acrylic etc… We will also complete generative design studies to generate a chassis that is both lightweight and strong.

As a group, we are extremely excited to complete this build as it brings together our love for electronics whilst providing a fulfilling challenge. Furthermore, by employing a range of manufacturing techniques to build the shell of the car we can learn about how different CNC machines work and the advantages / disadvantages of different manufacturing techniques.

A Focus on Electronics

Although this project has a very heavy focus on understanding what factors affect the aerodynamics of a cars speed, we also want to get stuck into some electronics. We found that the best way to assemble the RC car whilst not getting bogged down by overcomplicated electronics and wiring was to purchase a disassembled chassis of an RC car and heavily modify it to suit our needs: both ensuring that the manufacturing process of the electronics will be relatively smooth and allow us to disassemble and reassemble it to understand how it works.

How we plan for the electronics to work together: a high-level overview. The RC Car / Chassis / ESC section in our budget encompasses the required parts in that. By disassembling it we hope to further understand the inner workings of electronics required.

A Focus on Aerodynamics

We want the shell to resemble an F1 car as we want our RC car to be as fast as possible in a straight line in perfect conditions (no wind, ideal smooth racetrack). We want to accomplish this without using a “better” motor therefore we can make the car faster by making it slicker (aerodynamics).

To decrease the air resistance, we need to have the smallest possible cross-sectional area. We can accomplish this by reducing the height of our shell as much as possible. However, we also need to consider the how air can move round our car smoothly, for example if we were to make our shell a square, there would be a greater drag as a square is not an aerodynamically smooth shape, reducing efficiency and reducing top speed. Instead, our shell should be as smooth as a curve we can make it whilst fitting the electronics and chassis. This smooth shape will allow the air to flow over the car with little drag as possible as shown in the diagram.

We will also use a front wing to direct the air flow around the car allowing the air to flow smoothly, alternatively a rain-drop shape would also produce the effect of lease air resistance as it allows air to flow smoothly round the car with little resistance and low drag, however this is not practical as would not fit our chassis inside. Instead, we can combine these ideas to make a front wing that fits our car whilst creating the streamline affect (elongated rain-drop design).

Rear wings in F1 cars are used to direct the wind flow above the car thus giving the car more downforce so they can turn round corners at high speeds. Although we do not need to turn corners, we still need to have high downforce to get the best friction so that our motors can work at optimum efficiency. Wings also reduce the aerodynamic smoothness of the car thus slowing the car down (which is why F1 cars open their rear wing on the straight, leaving gap to decrease the drag but still have stability). Therefore, our rear wing should have a very slight angle at about 20° to the horizontal and be thin. This allows for our car to have increased downforce without gaining too much drag and ruining the aerodynamics of the car.

What will this require?

There are several materials and products that we will require in order to complete the project efficiently, and this section will act as a justification for each component labelled in our Budget requirement list (below):

• Firstly, we have decided to utilise ready built RC car models and disassemble them for the electronics parts and chassis structure. It is important to get several models so that we can test different shell shapes against each other simultaneously to ensure fair trails. For this we will require four RC car models – using them to study the disassembly process and internal hardware, make relevant modifications, and test different shell shapes and materials for the most efficient motor outputs.

• Our next crucial piece of equipment for this project is the 3D Printer, we choose the Flashforge because it has a dual extruder allowing for support material to be printer in soluble PVA meaning when we wash the model in warm water the supports dissolve away. This means that no long-term marks or scratches will be created by attempting to remove difficult support material. Furthermore, by having dual extruders we can improve aesthetics of the prototype and be able to visually segment the design. The Flashforge also has an enclosure allowing us to maintain relatively high temperatures to print in both ABS & TPU, also, by having an enclosure the printer is safer to use overall. The printer bed is heated allowing food good first layer adhesion which is essential for good quality output. Finally, for our experiments the material choice (weight, texture etc…) is very important and this printer allows us to print in a range of materials.

• Finally, we decided to consider the materials that we would need to create our shell models and prototypes in the form of 3D filaments. The main materials that we were keen on using were ABS – a rigid polymer with high tensile strength – and PLA – a biodegradable polymer known for its light weight and ease of printing due to its low melting point. Furthermore, we have decided to explore the use of high traction TPU filament and wood-filled PLA for an even lighter design. In order to print the complex shell shapes that we require, we need to also design stable printing support structures – for which we have decided to test out a soluble PVA filament (easily removed from 3D printed shells) with the dual extruder system of the 3D printer.

**Furthermore, we will be donating the 3D printer and excess materials to our school after using it for this project. This will allow for others to use the printer for their own projects and further their education in engineering, design & technology. **

Project Plan

Build RC Car: Assemble RC Car by employing the components mentioned in the B.O.M, this will be completed by following a number of guides online (ie. https://www.instructables.com/How-to-Make-a-Remote-Control-Car/ ). We hope that this stage of the project will be the most rapid allowing us to focus on the design of the car body. The RC car we will remove the wheels and 3d print new wheels out of TPU and maintain an ABS centre with reduced diameter allowing the frame of the car to be closer to the ground.

Air-Flow Analysis: Air flow analysis will be completed in MATLAB or Fusion 360. As we have experience in Fusion 360 after completing an online course in simulations in Fusion we will probably be going down this route. Firstly, we will model the chassis of the car in F360 and then complete the simulation analysis for it.

Design Car Bodies: We will design the car bodies by looking at existing solutions, drawing inspiration from nature and experimenting with a range of shapes and forms. We will also employ generative design to create forms that we wouldn’t have been able to materialise otherwise. Furthermore, the generative design will allow us to maximise the overall strength of the design whilst minimising weight.

Manufacture Car Bodies: The car bodies will be printed using ABS / PLA (and possibly machines out of MDF using our school’s CNC), we will employ the dual extruder to aid in printing support materials out of PVA so that they are soluble and can be easily removed. We will post-process the moulds using abrasive paper and acetone for the ABS which will be something that we’ve not tried out before but will provide a valuable learning experience.

Attach Car Body Onto Car: This will be done via M8 bolts that will go onto the modified chassis so that the shells can be easily swapped out and can be replaced easily so we can make modifications readily.

Measure Speed using Light Gates: Once we have the bodies manufactured and printed we will test them by using a 5 meter rule and light-gates. Using speed = distance / time we can find which car body is fastest and continually improve our car design so that it is the fastest it can be.

Project Specification

Budget

Project Funding is limited to 4 (of 5 people excl. Aiyush-G) bringing total to grant to $1000 ($250 x 4)