Pinewood Derby Car

In this Instructable, I will be illustrating the required steps to create a simple but fast Pinewood Derby Car. There is a lot of flexibility with each step in terms of design and application so don't worry if you do not have exactly the same equipment or materials that are pictured in this guide.

Safety Considerations: Ensure you are using proper PPE (glasses, gloves, ear muffs, etc) at all times and have the necessary supervision if required. Some of the machinery and tools used in this instructable require extreme care when handled.

Materials

• Standard Issue Pine Block
• 4x Nails (~2mm Diameter)
• Acrylic Sheet (Black) - Or 4x MDF Wheels
• Brasso Polish
• Small Weights (I used steel bars)

Tools

• Band Saw
• Laser Cutter
• Hand Drill
• Hammer
• Sandpaper
• Shaft Sanding Machine

The first and perhaps the most important steps is to design and cut out the chasis. On the side of your pine block, sketch the general shape of desired car and use a band saw or any type of saw to cut out the chasis.

Next, in order to smooth out the car's shape, go over the surfaces with sandpaper smoothing out any rough or uneven edges.

It is important to keep in mind that the center of mass of your car should be further back in order to maximise the starting GPE (gravitational potential energy) which will later convert to kinetic energy as your car is released down the track. This is why I wanted to make the front of the car as light as possible. Most races will have a weight limit for your car which is why moving weight from the front to the back is a good idea.

First, I used french curves to trace out a section of the car of both sides evenly. I then used a band saw to cut out the rough shape and then switched to using a shaft sanding machine to smooth out the sides evenly.

The wheels are tricky to get right because any angle to the nail could be the difference between losing and winning a race. First, mark out the holes where the wheels will go. I placed the wheels 20 - 25mm from the front/back end of the car and about 5mm above the bottom edge of the car.

If you are looking to be precise, use a hand drill with a drill bit of 1mm diameter to drill a small guide hole for each nail in the marked wheel spots. Threading the nail through the wheel and hammering it in place will work as well, just be careful not to bend the nail.

You should have a fully functioning car by now, however, if you are looking for speed, consider these tips.

1. Polish the nails - Doing this will reduce the coefficient of friction between the wheel and the nail (axel) which in turn will allow the wheels to turn more freely. This will help the car pick up speed as it hurtles down the track. First, sand the nail using sandpaper, and after, apply a polish or lubricant to help increase wheel spin.

2. Use Graphite - Graphite is a great lubricant and easily accessible to all. Just take a pencil and rub the graphite along the edge of the car where the wheel makes contact. This will help reduce the coefficient of friction between the wheel and the body of the car allowing the wheel to move more freely for increased speed.

3. Acrylic Wheels - If allowed by your competition, consider using acrylic wheels. They tend to be lighter and have a lower coefficient of friction compared to pine, thus reducing the force of friction between the wheels and the track. Unfortunately, this requires the use of a laser cutter to ensure wheel dimensions are precise with smooth edges.

Finally, it is time to add whatever remaining weight you have left to your car. It is important to maximise your weight as it plays an important part in winning races. While all cars accelerate down the ramp at the same rate (acceleration due to gravity is independent of mass), more weight will increase the time your car retains that speed on the flat section as a result of the law of inertia.

I cut the steel bars to lengths that would allow me to maximise the weight placement on the car and place them at the back of the car. However, do not place the weights too far back as that may result in your car flying off the track if the center of mass is not in front of the back axel. I ended up drilling two holes into the body of the car in order to secure the weights properly (if they shift during the race, it may cause the car to wobble into the rail quite a bit which dramatically increases friction and slows down that car).

After your weights are placed, that's it! Enjoy the win :)