Race car projects for kids are everywhere, but most fall short as classroom STEM activities. Pinewood Derby kits are expensive and need special tracks. Generic "build a car" tutorials are directionless - kids glue wheels on a block, roll it down a ramp, and that's the lesson. No real engineering challenge, no measurable goal, nothing to iterate on.

Cargo Crash Derby fixes all of that. Kids build race cars from cheap materials (craft sticks, hot glue, plastic wheels, axles) and tackle a real engineering challenge: design a car that carries as much cargo as possible (blocks or similar) down a ramp without spilling them. The goal is concrete, the results are measurable, and every run gives kids motivation and information to redesign, making this an ideal STEM project for elementary and middle school classrooms.

The project hits multiple STEM concepts at once. Kids see gravity and acceleration as the car rolls, and Newton's first law in action (cargo wants to keep moving when the car stops) so containment becomes a design problem. They work through structural engineering (a holder that won't collapse), center of gravity (tall cargo beds tip, low ones don't), and friction tradeoffs (more cargo means more speed, but also more force on the walls at impact).

I also love this project because it can be scaled for different ages and classroom constraints:

1. For example, younger kids can build exactly the same frame and wheels and just focus on how they design their cargo holder. Older kids can receive much less instruction and leave the whole design up to them.
2. If you have less class time, just a handful of tests can be satisfying and iterative.
3. You could also stretch this activity into 2+ hours by having everyone pause, watch each car roll down the ramp, and make observations about what is and isn't working before getting back to redesigning.
4. Finally, for a more competitive take, kids can race each other down the ramp to see whose car crosses the finish line (read: crashes) first.

Best of all, it's iterative by nature. Failure is fun and often unavoidable: cargo flies out, wheels wobble, cars crash and roll. Kids redesign, retest, and watch their numbers climb!

Supplies

This is a very open-ended project with no strict list of supplies. I used large colorful 6-inch craft sticks to make it easier for younger kids to build with, but smaller 4.5-inch craft sticks would also work just as well. This list of tools and supplies is more of a suggestion than a mandate.

Ramp setup:

1. Folding table
2. Cardboard
3. Something to stop the cars

Tools:

1. Hot glue
2. Scissors
3. Masking Tape

Supplies

1. Craft sticks
2. Plastic wheels
3. 1/8-inch dowels or bamboo skewers
4. Straws
5. Foam or wooden cubes
6. Rubber bands or pipe cleaners
7. Bonus: Googly eyes so kids can build a little driver guy - they love it!

Note: I strongly recommend limiting materials. Kids' instincts are to build a fortress-like structure on top of a car made of cubes. This is expensive, difficult to redesign, heavy, and ultimately does not foster creative solutions. Instead, try limiting kids to something like:

1. 30 craft sticks
2. 10 cubes
3. 5 rubber bands or pipe cleaners

This encourages more resourceful use of materials to create the most stable car and largest cargo hold possible.

Step 1: Prep the Ramp

The ramp can be anything that's sturdy and at least six feet long. I like using a plastic folding table with one set of legs collapsed.

To add extra challenge and excitement to this project, I also suggest creating a cardboard speed bump on the ramp as shown. This causes cars to fly into the air and hit the ground hard enough to jostle any loose cargo.

Then, two to three feet in front of the ramp, set up something that stops the cars. This can be a wall, a few heavy textbooks, another piece of wood, etc. The goal is to challenge kids further by having the car come to a sudden stop, which will throw loose cargo out of the car.

If you're planning on doing races, then set up a lane divider at the top center of the ramp, such as a square dowel.

Step 2: Show How to Make Rolling Wheels

I think this project works best when there's a balance of supporting kids with some fundamental building techniques while leaving the main challenge open-ended.

Making the wheels is one of those key techniques that needs to be shown.

Show kids how to make wheels by:

1. Inserting the dowel into the center of the plastic wheel, then taping the end
2. Sliding a straw over a dowel and putting another wheel on the other side

You can cut off the ends of the dowels to make it look a little neater, or trim the straw to make the entire wheel base narrower.

Step 3: Show How to Build an Incomplete Cube and Stick Structure

Another fundamental building technique for this challenge is using cubes to create sturdy vertical build points.

Kids tend to build structures by either stacking cubes one on top of another or by trying to glue the edges of craft sticks onto the build surface.

As mentioned earlier, building structures with just cubes is heavy and expensive. Building by gluing the edges of craft sticks is usually not very strong because the surface area of the craft stick edge is so narrow.

So instead, show how to use cubes not as a primary construction material, but as a sturdy point onto which they can build the main structure.

Demonstrating how to create an incomplete structure gives kids the building technique they need without showing a complete solution.

Step 4: Facilitate Tests

One thing I love about this project is that kids can quickly test on their own and are usually able to evaluate the results themselves. That said, you can still help facilitate tests by doing things like sending the kids' car down the ramp for them so they can sit near the finish line and watch the results more closely. Or, share observations or ask guiding questions to help lead them to effective redesigns after a test.

You can also help facilitate races, which work like this: one person holds the back of both cars. This is because it's a lot easier to coordinate the release of both cars at the same time by a single person. If each kid is holding onto their own car, it's more likely that one of them will release the car before the other.

Tech tip: One fun and extremely useful thing you can do is take slo-mo video on your phone. Not only is it super cool to watch the cars bounce and crash in slow motion, but it's actually useful because often times the cars are moving so fast that it's difficult to see how exactly the foam cubes are falling out. The slow motion video reveals details about their design that might elude kids' obervations otherwise.

Facilitate Races: The race rules I like to implement:

1. The winner is the person who reaches the finish line first and crashes at the end without losing a single piece of cargo
2. If one car reaches the finish line first but they drop some cargo, the other car reaches the finish line second but does not drop any cargo, then the car that does not drop any cargo is the winner.

Step 5: A Note on the Chassis Length