Battle Bot 2

Nickname: The Mill-itia

Project Objective:

The objective of this project was to design and build a competitive 3D-printed battle bot in just three days. The robot was intentionally designed to be manufactured almost entirely through FDM 3D printing, with only the necessary electronics and hardware added for functionality. This project challenged me to further develop my skills in design for additive manufacturing by creating complex geometries that could be printed without support material while accounting for the anisotropic nature of FDM-printed parts—the fact that their strength varies depending on the orientation of the printed layers. Every structural component was designed to maximize strength, maintain modularity, and keep tolerances tight despite the limitations of the manufacturing process. Beyond serving as a rapid design challenge, the project allowed me to leverage additive manufacturing to create geometries that would be difficult or impractical to produce using conventional subtractive manufacturing techniques. Restricting the project to three days also pushed me to improve my efficiency and design workflow. This project was also an opportunity to revisit an earlier battle bot design that exposed weaknesses in my understanding of structural design and additive manufacturing. By applying the lessons learned from that project, I was able to produce what I believe to be a significantly more robust and optimized design for competitive combat.

Although the design incorporates realistic manufacturing constraints and functional engineering principles, because of current resource limitations, it is not currently intended for fabrication or competition. Instead, this project serves as a focused CAD and design optimization exercise, allowing me to strengthen my skills in mechanical design, design for additive manufacturing (DfAM), and rapid engineering iteration under a constrained development timeline.

Weapon System:

The bot, nicknamed The Mill-itia, uses a large, rapidly spinning disk to store kinetic energy, then slams into its opponent to transfer it into a crushing blow. The disk is made up of a tough aluminum skeleton and aluminum striking pads sourced from a CNC manufacturing service, with a dense PC exterior to give the disk added weight and provide a mounting structure to attach it to the driving axle. The flywheel is driven by a Polyurethane belt from a brushless DC motor on the interior of the bot to keep the center of gravity low and to add a gear ratio of 1:2 to increase the torque output to the flywheel. Since the flywheel is a heavy, spinning, oblong shape, it wants to create many intense vibrations that can cause noise and damage to the bot. So to keep the flywheel stable, it's reinforced with 4 steel ball bearings to contain the rotation along one central axis. Those ball bearings are then anchored by two rigid control arms, mounted to the exterior of the bot.

Drive System

The drivetrain is powered by two independent brushless DC motors that drive a four-wheel system with tank-style steering, allowing the bot to pivot on the spot with precision. Each motor is paired with a 2:5 speed-reduction gearbox, which increases torque delivered to the wheels for stronger acceleration. This configuration prioritizes quick bursts of movement rather than high top speed, enabling the bot to make rapid, controlled maneuvers. Since the bot is relatively heavy, the enhanced torque not only improves responsiveness but also provides the necessary force for pushing and ramming opponents.

Electronics:

The battle bot utilizes a conventional RC control system, allowing me to leverage readily available components while maintaining a simple and reliable control architecture. User inputs are transmitted from a handheld RC transmitter to an onboard receiver, which relays the control signals to dedicated electronic speed controllers (ESCs). The ESCs regulate power delivery to both the drive motors and the weapon motor, providing precise speed and direction control. Thermal management was also considered during the design process. Ventilation openings were incorporated into the underside of the chassis to promote passive airflow while being positioned away from critical electronic components to minimize the risk of damage if the robot were to operate inverted. To further improve cooling performance, two 12 V, 40 mm fans are mounted at the rear of the robot, directing airflow across the ESCs and motors to help dissipate heat during operation.

Carbon Skeleton

Since this machine is scaled so large, and my printers aren't capable of printing each panel in one piece, the larger body panels were split into 2 sections. The issue is that tolerancing in between these panels to get a proper fit can introduce inconsistencies and create wobbles or flex between the seams of panels. Along with the issue that these seams would create weak points where an adhesive wouldn't compare to the same strength as the plastic bonds. To combat this flex and to increase the overall stiffness of the plastic itself, I've embedded an array of carbon rods into the structure of the panels, ensuring they cross over seams and join the different sections into one coherent, stiff assembly.

Rigid Frame

To enclose all the sensitive electronics and bring the structure together as a whole, the body of the bot is 3D printed from a carbon fiber-reinforced polymer called PA12-CF. PA12 is a nylon polymer with a 12-carbon chain, twice as long as the more common PA6. Both polymers share high strength and temperature resistance. However, the longer polymer chain in PA12 makes it more resistant to moisture absorption, which can be a significant issue with most other nylon polymers, leading to inaccurate parts that can deform and become brittle over time. The PA12 polymer also has a higher impact resistance due to its more flexible nature. Unlike PA6, which becomes very stiff, often leading it to shatter upon high-force impacts. The "-CF" represents the small carbon fiber strands embedded in the plastic. The main purpose of the carbon fiber isn't actually to strengthen the part, but rather to keep it from expanding. The issue with printing in nylon is that it loves to expand in high-temperature environments, such as when printing, because it has a high coefficient of thermal expansion. To combat this, small clippings of carbon fiber with a very low coefficient of thermal expansion are added to hold the polymer in place while it's being printed, so it can't expand.

Shock Absorbing Panels

While the tough PA12-CF panels do a great job of taking a beating, they can only withstand so much and serve better as a last line of defense. The real brute force is taken by the TPU exterior. TPU is a rubber-like filament used in 3d printing that has exceptional impact and abrasion resistance. Its high elasticity means that it can take many large hits and easily spring back to its original form with minimal damage. The high abrasion resistance also means that it can withstand wear and tear caused by friction or scraping. So no matter how many hits it takes, it won't significantly affect the material's lifespan. Leaving it just as strong after a battle as when it was first made.

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