Two years ago, I spent 26+ hours prepping a rubber band drag racer for a 4th grade class science project (my guinea pig class), and it was a complete BUST! Even after I worked out the kinks, unforeseen issues came up and things didn't go smoothly in the class. After spending 1 1/2 hours in class, kids were very disappointed with the result (imagine my frustration!).

After that project, I have a general rule of spending two to three hours to try it out, and if it doesn't work, I go on to another project. Well, I tried building a prototype with my daughter, and it went very well. I'm definitely going to use this project in the classroom this fall.

Step 1: Gather Your Supplies.

Balloon
Rubber bands
Straws
Thin bamboo chopsticks (skewers, lollipop stick, etc. will work, too)
Ruler
Scotch tape
Masking tape
~2" diameter circle maker
A piece of cardstock paper
A small screwdriver or an awl
Something to cut chopsticks
Scissors

Step 2: Tape Two Boxes Together.

Tape together the two boxes from the Origami Box project and set them aside.

Step 3: Create the Wheels.

Trace and cut out the six wheels with the holes for the axle in the center.

Step 4: Create & Assemble Axle Casings and Axle.

Mark and cut three axle casings to size (~1/2" wider than the vehicle body width).
Mark and cut three axles to size (~ 1" to 1 1/2" wider than the axle casing width).

An axle should freely slide in the casing.

Step 5: Assembling the "engine."

Insert a straw into a balloon.
Put a rubber band around the neck of the balloon over the straw.

DO NOT tie the rubber band too tight. It can collapse the straw, and it won't work well (I've learned from experience).

The bendy-side of the straw should be outside to direct the flow.

Step 6: Affix Axle Casings.

Tape the axle casings on the bottom of the vehicle.
Place rubber bands on the boxes. It gets more difficult to put on rubber bands after the wheels are attached to the axle.

The orange box is the front-end of the vehicle, and the green box is the back-end of the vehicle.

This rubber band configuration worked for me, but you can try others to keep the balloon and the straw in place.

Step 7: Wheels on the Axle.

Slide the wheels on the axle.
Fit them snugly on the axle (taping may be required later).

Surprisingly, this was the most difficult part of the project - sticking/taping/sliding wheels onto the axle. I wasn't satisfied with any of the processes of keeping the wheels on the axle, but all three ways work.

Step 8: Affix "engine."

Affix balloon and straw "engine" on the top of the vehicle.
The balloon should be supported, at least partially, by the front of the vehicle body (or else, it will go nowhere).

Step 9: Engage the "engine."

Blow up the balloons and have a race!

Step 10: Additional Notes.

In the process of building this vehicle for the blog and instructables.com, I built three and learned a lot in the process.

I found it challenging to make the vehicle go straight. There were a lot of variables to consider, but the most important one is to make sure that the axle casing is taped on straight. Also, flattening out or smoothing out the warped wheels helped, but the results were mixed. I might have to tinker with this longer.

This project was a surprise because I expected it to take longer. But it didn't, and I was really happy with what I was able to finish in the time I've allotted for myself. I could have cut out even more time by using a single serve cereal box or other smaller movie-sized candy box, but as I said, I wanted uniformity in classrooms.

Here's the Youtube link for the video:

Air-powered vehicle testing video

Thanks and have fun!