3d printed pinewood derby car

Introduction to 3d printed pinewood derby cars

The pinewood derby is a classic Cub Scout event that challenges young participants to design and build a small, unpowered car that races down a wooden track. Traditionally, these cars are crafted from a provided block of pinewood, axles, and wheels. However, the advent of 3D printing has opened up entirely new possibilities for design and construction. A 3d printed pinewood derby car allows for greater precision, intricate geometries, and innovative weight distribution strategies that were previously impossible.

This article will guide you through the process of designing, printing, and assembling a 3D printed pinewood derby car that has the potential to be a top contender.

Design considerations for speed and performance

The key to a fast pinewood derby car lies in understanding the physics involved. Several factors influence a car's speed, including weight distribution, aerodynamics, friction, and wheel alignment. When designing a 3d printed pinewood derby car, you have considerable control over these parameters.

Weight distribution:

A rear-weighted car is generally faster. The potential energy at the top of the ramp is converted to kinetic energy as the car rolls down. A rear-weighted car stores more of this energy, resulting in higher acceleration at the start of the track. Experiment with different weight placements within your 3D model to find the optimal configuration. Consider adding small cavities within the design to accommodate tungsten weights, which are denser than steel or lead and provide more concentrated mass.

Aerodynamics:

While the pinewood derby track is relatively short, minimizing air resistance can still make a difference. Streamlined designs, such as a teardrop shape or a wedge, can reduce drag. Use computational fluid dynamics (CFD) software (even a simplified version) to simulate airflow around your design and identify areas of high drag. Adjust the shape accordingly. A real-world example is the use of a "cowl" to direct airflow smoothly over the front wheels.

Wheel alignment and axle polish:

Even with a perfectly designed body, misaligned wheels or rough axles can significantly slow your car down. Ensure that your axles are perfectly straight and polished to a mirror finish. Use a fine-grit sandpaper followed by polishing compound to achieve this. Some racers even use a lathe for ultimate precision. Also, ensure that the axles are perpendicular to the car body for proper wheel alignment. You may need to file or shim the axle slots to achieve perfect alignment.

Choosing the right materials and 3d printing settings

The material you choose for your 3d printed pinewood derby car can affect its weight, strength, and performance. PLA (Polylactic Acid) is a common choice due to its ease of printing and relatively low cost. However, ABS (Acrylonitrile Butadiene Styrene) is stronger and more heat-resistant, which might be beneficial in certain environments. PETG (Polyethylene Terephthalate Glycol) is another good option that balances strength and ease of printing.

Printing settings:

Optimizing your 3D printing settings is crucial for achieving a smooth, accurate print. Here are some key settings to consider:

• Layer Height: A smaller layer height (e.g., 0.1mm) will result in a smoother surface finish, which can reduce friction.
• Infill Density: Adjust the infill density to control the weight of your car. Experiment with different infill patterns (e.g., honeycomb, gyroid) to find the optimal balance between strength and weight.
• Print Speed: Slower print speeds generally result in higher quality prints with fewer imperfections.
• Support Structures: Use support structures sparingly, as they can be difficult to remove cleanly and may leave behind imperfections on the surface of your car.

Assembly and fine-tuning

Once your 3d printed pinewood derby car body is printed, the next step is to assemble it and fine-tune its performance. This includes inserting the axles and wheels, adding weight, and making adjustments to wheel alignment.

Axle and wheel installation:

Carefully insert the axles into the axle slots. Ensure that the wheels spin freely without any binding. If necessary, you can lubricate the axles with graphite powder or a specialized lubricant designed for pinewood derby cars. Some participants will also "break in" their wheels by spinning them at high speed for extended periods to smooth out any imperfections.

Weight adjustment:

Fine-tune the weight distribution by adding or removing weight as needed. Use small pieces of tungsten putty or lead tape to make precise adjustments. The ideal weight is typically around 5 ounces, the maximum allowed by most pinewood derby rules.

Wheel alignment refinement:

Use a track or a flat surface to check wheel alignment. If the car veers to one side, gently bend the axles to correct the alignment. This can be a delicate process, so proceed with caution. A slight toe-in (where the front of the wheels are slightly closer together than the back) can sometimes improve stability.

Advanced techniques and winning strategies

For serious competitors, there are several advanced techniques that can further enhance the performance of their 3d printed pinewood derby car:

Rail riding:

This technique involves deliberately misaligning one of the front wheels so that it lightly rubs against the track guide rail. This can reduce friction and improve speed. However, rail riding requires precise adjustments and can be risky.

Bent axles:

Bending the axles slightly can reduce the contact area between the wheel and the axle, which can reduce friction. This is a delicate process that requires specialized tools and experience.

Polished wheels:

Polishing the wheels to a mirror finish can further reduce friction. Use a fine-grit polishing compound and a rotary tool to achieve this.

Graphite lubrication:

Applying a thin layer of graphite powder to the axles can significantly reduce friction. Be careful not to over-lubricate, as too much graphite can attract dust and debris.

By carefully considering these design principles, material choices, and assembly techniques, you can create a 3d printed pinewood derby car that is both visually stunning and incredibly fast. Remember to test and iterate on your design to optimize its performance for your specific track.