Getting a Pinewood Derby car to ride on 3 wheels can be a fun challenge for scouts and parents alike. The Pinewood Derby is an iconic event for Cub Scouts where participants race homemade cars down an inclined track. The standard car design has 4 plastic wheels, but modifying the car to ride on just 3 wheels requires some creative problem-solving and engineering.
In this article, we’ll walk through the full process step-by-step, covering the pros and cons of a 3-wheeled design, weight distribution considerations, wheel placement configurations, axle options, and testing procedures. With some careful planning and experimentation, you can get that 3-wheeled Pinewood car flying down the track!
Page Contents
The Pros and Cons of a 3-Wheeled Design
Switching from 4 wheels down to 3 offers some distinct advantages as well as disadvantages to consider:
Pros
- Lower friction and drag – Having one less wheel touching the track means less overall friction slowing the car down.
- Better tracking – Properly balancing a 3-wheeled car can result in better steering control and tracking around curves.
- Unique look – Visually, a 3-wheeled car stands out from the pack.
- Challenge – Mastering the 3-wheeled design provides a great engineering challenge.
Cons
- Harder to balance – With fewer contact points, the center of gravity must be optimized to avoid tipping.
- Requires weight modifications – Getting the weight distribution right is critical.
- Increased risk of steering issues – Reduced stability can lead to steering problems.
- Wheel placement limitations – Options for wheel placement are more constrained.
As with any design change, there are trade-offs to consider. For scouts and parents willing to problem-solve and experiment, a 3-wheeled car presents a rewarding project with ample opportunity for learning.
Weight Distribution Considerations
One of the biggest challenges with switching to a 3-wheeled Pinewood Derby car is getting the weight distribution right. With only 3 points contacting the track instead of 4, you’ll need to optimize the location of weight inside the car to maintain balance and avoid tipping over.
Here are some key weight distribution considerations when designing a 3-wheeled car:
- Lower the overall center of gravity – Keeping weight lower in the car body improves stability.
- Position weights towards the rear – Placing weight above or behind the drive axle helps avoid front tip-overs.
- Add weights incrementally – Add weight slowly, testing balance after each addition.
- Consider asymmetric weight placements – Offsetting weights can counteract imbalances.
- Make adjustments based on trials – Let test runs guide where weight needs adjusting.
Experimenting with different weights and placements is the best way to hone in on your specific car’s optimal balance point. Keep weight placements adaptable by using methods like lead tape so adjustments can be made easily. Take test runs on a short practice track before going for maximum speed.
Wheel Placement Configurations
With a 3-wheeled design, choosing where to place the 3 wheels on the car presents some options to consider:
Rear Tripod (2 Rear, 1 Front)
This configuration uses 2 rear wheels placed wide apart for stability, with 1 front wheel for steering. The 2 rear wheels provide a solid base to balance the car on while concentrating weight forward. Angling the front wheel slightly left or right gives steering control.
Front Tripod (2 Front, 1 Rear)
A front tripod flips the wheel layout, with 2 front wheels and a single rear wheel. This can provide good traction from the front wheels with the rear wheel steering. Weight distribution is more challenging since the rear can tip up easier.
Left/Right Dual (2 Left or Right, 1 Opposite)
Rather than a tripod, this places 2 wheels on one side with the solo wheel on the other side. For example, 2 right wheels with 1 left wheel. This forces most of the car’s weight to the dual wheel side. Quick left/right weight shifts can steer the car.
Straight 3 In-line
The wheels can also be kept in a straight line, though this lacks the lateral stability of wider tripod configs. Small weights shifts steer the car. A symmetrical weight distribution is critical to avoid tipping.
Each wheel placement setup has pros and cons to weigh when deciding on the design. Testing different placements is the best way to determine what works optimally for a specific car.
Axle Options
To allow smooth rolling on just 3 wheels, choosing the right axle setup is important. Here are some axle options when converting a Pinewood Derby car to 3 wheels:
- Standard nails – Use just 3 of the 4 angled nails included in the kit.
- Bent paperclips – Paperclips bent into L or V shapes work as custom axles.
- Wooden skewers – Sharpened bamboo skewers can substitute for nails.
- Threaded rod – Miniature threaded rods with nuts allow wheel adjustments.
- Aftermarket axles – Specialty axles help optimize wheel placement.
Consider the car weight, wheel configuration, and needed adjustability when selecting axle types. Smooth rolling axles help minimize friction. If using nails, carefully filing any burrs is recommended.
Testing and Optimization
The best designs require extensive testing, and 3-wheeled Pinewood Derby cars are no exception. Follow this general testing process:
Check Rules on 3 Wheels
Always check your local Pinewood Derby rules, as some races prohibit non-4-wheeled car designs. Don’t assume 3 wheels will be allowed.
Start with No Weight
Do initial tests rolls with just the bare 3-wheeled car to assess basic balance and tracking.
Add Weight Slowly
Incrementally add weight in small amounts, testing after each addition. Use weight placements you can adjust like lead tape.
Try a Ramp Before the Track
Use a small ramp to test how the car tips and rolls before attempting a full track run. Adjust weight based on ramp tests.
Test on Practice Track Sections
Run on a short section of track before going the full distance. Check for tipping, rolling, and steering issues.
Collect Speed Data
Use a sloped ramp to test speed. Time trials with a stopwatch can help compare runs during optimization.
Watch for Over-optimization
A car optimized for a particular track may not perform as well in race conditions on an unfamiliar track. Find a good overall balance.
With careful iteration and controlled experiments, you can dial in an excellently tuned 3-wheeled Pinewood Derby car ready for race day.
Conclusion
Switching a standard 4-wheeled Pinewood Derby car to a 3-wheeled design takes some thoughtful engineering, but can result in a uniquely fast racer. Keys to success include optimizing the overall weight distribution, choosing an effective 3-wheel configuration, using suitable axles, and exhaustive prototyping and testing. While tricky, with some persistence and learning from failures, getting that aerodynamic 3-wheeled car to fly straight and true down the track is an achievable goal. Whether you take home the trophy or not, the skills gained from conceptualizing, building, and refining a creative 3-wheeled Pinewood Derby car will stay with you.