Revving Up Innovation: A Practical Learning Project for Creating a RC Car
Olver Farace, Alireza Sabbaghi, and Logan Maurer
Mechanical Engineering, University of Wisconsin-Madison, USA
Abstract
This project explores the design, manufacturing, and evaluation of a mini remote-controlled (RC) car using various additive manufacturing techniques. Our goal was to create a fully functional RC car that balances functionality, cost, and educational value. The car was designed with core requirements including four wheels, steering capabilities, remote control functionality, and battery operation. We utilized Fused Deposition Modeling (FDM) for its accessibility and adaptability, allowing us to experiment with different materials such as PLA, PETG, TPU, and Nylon, chosen for their unique properties. Additionally, for components requiring higher precision and intricate details, Stereolithography (SLA) was incorporated into our manufacturing process. The project also focused on optimizing print settings to enhance production efficiency and material use, implementing strategies such as reduced infill and adjusted layer heights. Our findings demonstrate that the mini RC car functions as intended, with mobility and basic operational capabilities successfully achieved. However, the project also identified challenges related to thermal warping and tolerance issues, which were mitigated through design revisions and material adjustments. The project concludes with suggestions for future improvements in speed and aesthetics, along with further development as an educational tool for students interested in electronics and 3D printing. This project underscores the potential of additive manufacturing in prototyping educational tools and highlights the practical applications of integrating electronics with mechanical design.
Introduction
The rapid advancement of additive manufacturing technologies has revolutionized various industries, offering significant improvements in speed, cost-efficiency, and customization capabilities. Among these, Fused Deposition Modeling (FDM) and Stereolithography (SLA) are notable for their widespread application in educational and prototyping environments. This project leverages these technologies to design, build, and evaluate a mini remote-controlled (RC) car, showcasing the integration of mechanical components and electronics within an educational context.
The initiative for this project stemmed from a dual objective: to provide a hands-on learning experience in additive manufacturing and electronics and to explore the feasibility of producing functional mechanical devices using predominantly 3D-printed parts. The mini RC car was conceptualized to meet several foundational requirements—namely, mobility, steering capability, remote operation, and battery power. These criteria were set to ensure that the final product would be functional and engaging, serving as an effective educational tool.
This report details the journey from the initial design stages, through the manufacturing process, to the final testing and evaluation. It covers the selection of materials and technologies, challenges encountered in the design and fabrication phases, and the solutions implemented to address these issues. Through this process, the project aims to illuminate the practical challenges and learning opportunities presented by additive manufacturing in a real-world application.
Ultimately, this project not only tests the limits of current 3D printing technologies in creating dynamic and functional machines but also aims to inspire future engineers and enthusiasts by demonstrating the accessibility and potential of modern manufacturing techniques.
Vehicle Architecture
The architecture of the mini RC car has been meticulously designed to optimize performance, durability, and ease of assembly. The vehicle comprises several distinct yet interdependent systems that contribute to its overall functionality. Below is a breakdown of the main architectural components and their design considerations.
Figure 1. CAD Assembly
Frame and Chassis
The frame serves as the backbone of the RC car, providing structural integrity and a platform for mounting other components. It is constructed using Fused Deposition Modeling (FDM), allowing for rapid prototyping and modifications during the design phase. The chassis layout is designed to distribute weight evenly for improved stability and handling. It includes specific mounts for the motors, battery pack, and control systems, ensuring a compact and efficient assembly.
Figure 2. Initial Design
Drive System
The drive system is engineered for reliability and performance. It features dual electric motors that drive the rear wheels, offering a balance between speed and torque. A simple yet robust transmission system connects the motors to the wheels through a pulley system that is also 3D printed.
Figure 3. Major Overhauls Front View
Figure 4. Major Overhauls Side View
Steering Mechanism
Steering is achieved through a servo-controlled linkage system connected to the front wheels. The servo is strategically positioned on the chassis for direct actuation of the steering tie rods, minimizing latency and maximizing response time. The steering system’s design allows for precise control, essential for navigating tight turns and maintaining stability at higher speeds.
Wheels and Tires
The wheels are designed with a focus on durability and traction. They are made using a combination of PLA for the core and TPU for the tires, offering a good balance between rigidity and grip. The tread pattern on the tires is optimized for various surfaces the car might encounter, enhancing its versatility.
Aesthetic and Protective Body
The body of the car not only enhances its aesthetic appeal but also serves as a protective shell for the internal components. It is designed to provide ample coverage against dust and debris. The body is fabricated from PLA so that it is easily replaceable if it gets cracked.
Figure 5. PLA Bodies
Materials
Using the correct materials in this RC car is a crucial aspect of the project. It was decided early on in the process of developing the car, the majority of parts should be printed with Fused Filament Fabrication (FFF). This would limit material choices to common thermoplastics. The most common thermoplastics for FFF are PLA and ABS.
In the early stages of prototyping, it was decided to use PLA for printing and transition to a different material after verification. PLA is rather inexpensive compared to the use of other materials. It also offers easy printing compared to most other thermoplastics, not requiring a heated build plate or chamber. After all the parts were verified to fit together the parts were made in PETG.
PETG was chosen to make the car due to its better material properties. PET is a common material used to make plastic drinking bottles. It offers decent environmental sustainability and better strength than PLA. PETG is a modified PET with a glycol added to it. This glycol allows PETG to be printed at a lower temperature, allowing for machines to print it. The glycol does make the PET a bit softer, which does increase toughness a bit. PETG surpasses PLA in its environmental stability meaning it will stick around longer, but is also one of the thermoplastics that can be recycled.
A critical part of any car is the tires and their ability to maintain grip on the ground. PETG and PLA have relatively low static friction values on metallic and smooth wood surfaces. For this reason, it was decided to try and print a TPU and Nylon tire that would go on the wheels. These materials are usually quite difficult to print on hobby-grade 3D printers. The group was successfully able to print the Nylon tire after a few failed attempts. After several failed attempts with the TPU tire, it was decided to scrap this endeavor. Highly Flexible filaments such as TPU are notoriously difficult to print with. This is usually an inherent issue with how the material is pushed through the nozzle in FFF printing. The filament since it is so flexible tends to deflect instead of being pushed into the extruder.
Figure 6. PLA Wheel
Figure 7. Nylon Wheel
Electrical
A critical aspect of an RC Car is making it move. To have adequate torque to make the vehicle move it was decided to use two small electric motors. A servo would be used to drive the front wheels left and right. An inherent bonus of using two motors is it opens up the ability to use tank steering or torque vectoring. Tank steering is where no servo steering input is used and it is just different motor speeds that rotate the vehicle. Torque vectoring could be used as an artificial diff. Since both motors drive the back wheels at the same speed, taking corners would cause the inside wheel to slip. This could be fixed by varying the speed
A Raspberry Pi Zero W would be used as the main control board for the RC Car. Initially, the group wanted to use an Arduino Uno but after looking at the cost of sourcing a radio receiver or building one it was decided the Raspberry Pi was cheaper. To control the car using the Raspberry Pi Zero a Bluetooth signal instead of a radio signal would be used. An added advantage of the Raspberry Pi is its single-board computing power and it has a real user interface. This makes programming and debugging the vehicles easier.
The overall electrical schematics work in this way. A Raspberry Pi Zero W runs a Python script. This drives pins on the Raspberry Pi high and low which interface with a servo and L298N motor controller. The servo takes a digitally created PWM signal from the Raspberry Pi. The L298N just receives on and off commands for both motors. Additional AAA batteries are used to power the motor controller. A separate portable battery bank is used for the Raspberry Pi since it has very tight voltage requirements.
Figure 8. Electrical of RC Car
Programming
To make the car drive properly a program is needed to control it. Since a Raspberry Pi is used as the main control board all programming can be done using Python. This programming can be done using the Raspberry Pi’s integrated User interface. The program then can be automatically started on boot up of the Raspberry Pi.
To control the servo steering and motors a Bluetooth keyboard is used. Once the keyboard is attached to the Raspberry Pi it behaves like any regular keyboard. The program reads key inputs and sends signals accordingly. The keys “WASD” and space bar were chosen to control the vehicle since they are ubiquitous in video games. The program continuously searches for key inputs from the keyboard and once it finds one it sends the associated signals to start motors or turn the servo. To control the servo a PWM signal is used. Different signal frequencies are sent to control the servo. This can be set up in a way that the servo returns to the center or its specified right or left positions given this frequency.
Vehicle Body Design
In addition to the structural considerations, the design of the vehicle body played a crucial role in both the aesthetic appeal and functional performance of the mini RC car. The body not only protected internal components but also contributed to the overall aerodynamics and maneuverability of the vehicle.
Rapid prototyping facilitated the exploration of various body designs, allowing for quick iteration and optimization. Initially, the focus was on creating a lightweight yet robust shell that could withstand impacts while maintaining a sleek appearance.
Furthermore, the incorporation of mounting points and access panels within the body design facilitated easy maintenance and component replacement, reinforcing the modularity and versatility of the overall vehicle architecture. This modular approach not only simplified assembly but also allowed for future upgrades and customization options, encouraging continued exploration and experimentation.
Overall, the design of the vehicle body was a balance between form and function, with a focus on both aesthetic appeal and practical performance. By harnessing the capabilities of additive manufacturing, the body design evolved iteratively to meet the project’s objectives while showcasing the potential of modern manufacturing techniques in realizing complex and customized designs.
Rapid Prototyping advantage
A large majority of the structural parts for the vehicle are made using FFF. This allowed the largest part of the car, the frame to be printed in under 3 hours. Most of the smaller parts such as the wheels and mounts can be printed in under half an hour. All required parts printed together took less than 10 hours on a Prusa MK3S. This can all be done on a print bed that is smaller than 200 mm x 200 mm. Which is a very standard size for hobby-grade FFF printers.
This rapid iteration time proved to be quite useful for our project. Since most parts could be printed in under an hour if something didn’t fit quite right the first time it could be printed again. The reason most components wouldn’t fit together correctly was thermal warping or extrusion tolerance. As parts are printed at high temperatures they are in an expanded state as they cool they will shrink. This causes fitment to be off between parts. A tolerance will need to be added to account for this. This came up several times during the build process since each material has its thermal coefficient of expansion yielding different tolerances.
A significant iteration of the vehicles was how the wheels were attached. The wheels have to be attached in a way that reduces rolling friction. If this friction is too high it becomes too hard to drive the vehicle or make it move. The original wheels had the axles printed in the wheel. The bearings had an internal diameter of 3mm. This proved to be too small and printing the tall axels on the wheels would often move resulting in poor print quality. Since the front wheels didn’t need long axles they printed just fine and fit as intended. To accommodate longer axles in the back a different method was used. The print-in-place axles were removed and replaced with holes. They would then be put together using a leftover filler rod from a welding station. This proved to work quite well and reduce the rolling friction of the wheels.
The other significant iteration focus was the drive train. The RC Car uses a belt-driven system to move the vehicle. Originally the drive pulleys that were printed could not produce enough torque to move the vehicle. It was decided at this point to make the drivetrain a two-stage drivetrain. Stepping up the torque twice from two different pulley arrangements. This proved to do the trick and it was able to spin the wheels.
Vehicle Performance
The performance of the mini RC car was a culmination of careful design considerations, material selection, and electronic integration. While the vehicle achieved basic operational goals, such as mobility and control, several challenges and opportunities for improvement were identified during testing and evaluation.
The choice of materials, particularly for the tires, also influenced the vehicle’s performance characteristics. While PETG and PLA provided structural stability, the use of TPU for tire construction highlighted the importance of grip and flexibility in achieving optimal traction and handling on various surfaces. Despite the initial challenges with printing flexible filaments, the successful integration of TPU tires demonstrated the benefits of utilizing specialized materials for specific functional requirements.
Additionally, the selection of electronic components, including the Raspberry Pi Zero W as the main control board, facilitated advanced programming capabilities and enhanced user interface options. This choice not only streamlined the integration process but also allowed for future expansion and customization through software updates and additional peripherals.
In conclusion, by addressing these challenges iteratively and leveraging the modularity of the design, the project demonstrated the potential of modern manufacturing techniques in realizing functional and customizable mechanical devices.
Discussion
The design and implementation of the mini RC car project effectively demonstrated the capabilities of additive manufacturing techniques in creating functional mechanical devices. Through the course of this project, several key insights were gained, particularly in the realm of integrating mechanical and electronic components within a compact and efficient design.
One of the principal challenges encountered was managing the thermal warping of components during the 3D printing process. This issue was particularly prevalent with materials like PLA and PETG, which necessitated several design iterations to achieve the desired tolerances and fit. The successful integration of a modular design allowed for easier troubleshooting and replacements, highlighting the advantages of modularity in educational and prototyping environments.
The use of a Raspberry Pi as the control system demonstrated the feasibility of incorporating sophisticated computing power into small-scale RC vehicles. This choice not only provided cost efficiency but also allowed for a higher level of programming flexibility and ease of integration with various input devices.
Furthermore, the project provided practical insights into the limitations and potential of different materials used in 3D printing. For instance, the use of TPU for tires highlighted the benefits of using flexible materials for specific applications where grip and flexibility are paramount.
Overall, the project underscored the importance of iterative design and testing in the engineering process, particularly when dealing with new technologies and materials. The ability to rapidly prototype and refine component designs was invaluable and is a testament to the evolving nature of additive manufacturing technologies.
Conclusions
This project successfully met its primary objectives of designing, manufacturing, and testing a functional mini RC car utilizing additive manufacturing techniques. The integration of Fused Deposition Modeling (FDM) and Stereolithography (SLA) 3D printing processes proved essential in creating an educational tool that demonstrated the practical applications and possibilities of these technologies.
While the vehicle achieved basic operational goals, including mobility and control, one notable limitation was its speed. The car performed slower than anticipated, which highlighted important considerations regarding the power-to-weight ratio and the efficiency of the drive mechanism. This aspect of the project underscored the need for further optimization in motor performance and possibly a reassessment of the materials used for structural components to reduce overall weight.
Moving forward, enhancing the car’s speed and handling characteristics presents a significant opportunity for future iterations. Improvements might include refining the gear ratios, exploring lighter or more rigid materials for construction, and advanced electronic controls for better power management. Additionally, focusing on the aesthetic aspects and improving the durability of the printed parts could increase the project’s appeal and educational value.
In conclusion, despite the challenges with speed, the mini RC car project served as a valuable educational platform, providing hands-on experience in mechanical design, electronics, and programming. It effectively demonstrated the accessibility and potential of modern additive manufacturing techniques, paving the way for future projects that could further explore and expand upon the capabilities demonstrated here.
References
- J. Davenport, Materials Transformation Center, personal communication.
- M.A. Spalding, G.A. Campbell, F. Carlson, and K. Nazrisdoust, SPE-ANTEC Tech. Papers, 52, 792 (2006).
- C.I. Chung and R.A. Barr, U.S. Patent 4,405,239 (1983).
- S.A. Somers, M.A. Spalding, J. Dooley, and K.S. Hyun, SPE-ANTEC Tech. Papers, 41, 222 (1995).
- Anderson, R. (2018). Additive Manufacturing: An Overview of Technologies and Applications. CRC Press.
- Gibson, I., Rosen, D.W., & Stucker, B. (2015). Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing. Springer.