3D Printed RC Car v2

Overview:

The objective of this project was to build an RC car. I designed and 3D printed all the parts for the chassis and body. It uses RC components, standard fasteners and hardware.

Specs:

• Drive Type: Rear-wheel drive using a GT2 belt and pulley system (20T motor pulley to 50T axle pulley)

• Steering: Front-wheel steering using a servo-driven 4-bar linkage

• Battery: 2S LiPo (7.4V, 2000mAh)

• Motor: A2212 2200KV brushless outrunner motor

• ESC: 30A brushless ESC

• Top Speed: ~20 km/h (on-road, tested)

• Chassis: Fully 3D printed, modular for easy access and repairs

• Control: 2.4GHz RC transmitter and receiver

Design:

The car was designed using Onshape. Every part of the chassis, drivetrain, and steering system was built to be 3D printed and easily assembled. The design is modular and easy to take apart for maintenance or upgrades.

The design consisted of 4 main subsystems: frame, steering assembly, electrical housing, drive assembly

Frame:

The frame is laser cut and contains holes to fasten the steering assembly, drive assembly, electronics housing, and the bumpers together. The frame is cut out of an 1/8 in acrylic. 

Since acrylic is a brittle material with low ductility, it tends to crack under impact or high stress rather than deform. Because the frame receives loading and impact energy transferred from the bumper, I added fillets at key stress points. These fillets reduce stress concentrations by spreading out the force, which helps prevent cracking and increases the durability of the acrylic frame.

I did a quick analysis of the frame given a large load derived from a general impulse force given a max speed and the cars weight. This analysis gives a good visual of the localized stresses in the frame allowing for fillets to be added to the frame geometry. 

Frame without Fillet Stress Analysis

There are significant stress concentrations in the corners between the steering assembly and the drive assembly (circled in red). Under a high-impact load, these localized stresses could exceed the material’s fracture toughness, leading to crack initiation and propagation. Over time or under a large impact, this would likely cause the front of the car to separate from the rear structure. 

Frame with Fillet Stress Analysis

After adding fillets to these corners, the localized stress is distributed reducing the potential for the frame the crack.

To further reduce the forces transmitted to the frame during a crash, I added a cardboard bumper to act as a crumple zone, similar to those used in full-scale vehicles. The bumper increases the impact duration, reducing the peak force experienced by the structure according to the impulse-momentum relationship. Additionally, the cardboard bumpers are inexpensive and easy to replace, allowing kids to drive the RC car into obstacles at full speed without damaging any critical components. 

Steering Assembly:

The steering assembly is controlled by a 9g servo. It uses a 4 bar linkage mechanism to transfer the rotation of the servo to the steering knuckles. 

Drive Assembly:

The drive system uses a rear-wheel drive setup powered by an A2212 2200KV brushless motor. A 20T GT2 pulley mounted to the motor shaft drives a 50T pulley on the rear axle using a GT2 timing belt, giving a 2.5:1 gear reduction. This increases torque and reduces top-end RPM to a more usable range for ground contact. The axle is supported by 608 bearings. The aluminum axle transmits the power from the pulley to the wheels. The assembly is bolted to the lower chassis, and belt tension can be adjusted via a M5 bolt.

To maintain proper belt tension, the motor mount is designed with a tensioning mechanism.  The motor sits on a slotted mount that interfaces with matching slots on the drive frame. A tension bolt allows the motor to slide linearly away from the rear axle keeping the motor parallel to it. This ensures consistent belt alignment and makes it easy to adjust tension or replace the belt without affecting motor orientation. 

3D Printing and Design Techniques:

To ensure the parts were strong, functional, and easy to assemble, I applied several 3D printing techniques throughout the build: 

Borrowed Tolerances from M3 Hardware
Many of the mounting holes and pockets were designed using the known dimensions of standard M3 nuts and bolts. By designing around these known tolerances, I could ensure that parts would press-fit or seat cleanly without post-processing. For example, hexagonal cutouts for M3 nuts were sized slightly undersized (~5.4–5.5mm flat-to-flat) so that nuts could be pressed or tapped into place and held securely by friction alone, turning printed parts into functional mechanical components.
I also embedded M3 nuts into the prints. This required an internal pocket to be made in the 3D model. The print is then sliced and pauses added at the layers before the internal pocket is covered. The nut is then inserted into the part and the print resumed. This is a very helpful technique as it allows for the threading of the bolt to be implemented into the print--plastic parts tend to strip if over torqued or after fatigued use.

Purposeful Print Orientation

Each part was oriented during slicing to align with the direction of load. For parts that experience bending or impact the layers were aligned so that stress runs along the filament paths rather than across them. This helps reduce layer delamination and shearing, where parts split along layer lines under stress-- this layer shearing is is one of the biggest drawbacks with FDM printing. I provided an image that gives an example of how the bracket used to secure the axle bearings is printed on its side to prevent perpendicular loading on the print layers.

Higher Wall Count for Strength 

To make the prints more durable, I increased the wall/perimeter count in the slicer settings. Most structural parts were printed with at least 3–5 perimeters, which results in more solid, shell-dominant prints. This technique reinforces the outer walls, where stress tends to concentrate, and improves the part’s resistance to cracking or flexing--especially useful when using materials like PLA, which can be stiff but brittle.

Electonics:

Components:

• Motor: A2212 2200KV brushless outrunner motor

• ESC: 30A brushless ESC rated for 2–3S LiPo

• Battery: 2S (7.4V) 2200mAh LiPo battery

• Steering Servo: MG90S micro servo for front-wheel steering

• Receiver: 2.4GHz RC receiver (paired with a hobby-grade transmitter)

System Overview

• The motor connects to the ESC, which handles power delivery and throttle control

• The ESC and steering servo are both plugged into the receiver, which interprets signals from the transmitter

• Power from the battery is routed through the ESC, which also powers the receiver 

• The steering is driven by the servo, which actuates a 4-bar linkage to turn the front wheels

Summery: