Self-Defeating Fan Car

On your marks, get set, stay put! Have you ever that get up and not-go feeling? Well this car feels it, too. With a fan in the front and a sail in the back, you'd think it would be the perfect self-contained contraption. After all, it's a sail car that can make it's own wind, right? It wants to go everywhere, but ends up going nowhere.

The self-defeating fan car is one of my favorite contraptions, and it has a secret to escape from its stillness. This project is a great puzzle, a way to chat about Newtonian laws and forces, and of course, to be just downright silly.

This car's biggest enemy is itself. But you can help it out and make it go.

• What: Self-Defeating Fan Car
• Why: for the metaphors and the physics
• Concepts: forces, motion, physics, Newton's laws, air pressure
• Time: ~ 30 minutes
• Cost: ~ $2
• Materials:
  • Cardboard
  • Some motor support material (I used wood)
  • Motor (1.5V-4.5V motors work great)
  • Battery and wiring (I used a 9V)
  • Craft sticks x 2
  • Paper
  • Straws x 2
  • Wood skewers x 2
  • Wheels x 4 (checkers, CDs, bottle caps)
  • FAN OPTION 1: Propellor (can buy on Amazon)
  • FAN OPTION 2: Plastic bottle with cap
• Tools:
  • Cutting tool (scissors or X-acto)
  • Hot glue gun
  • Soldering iron (optional)

Let's get (not) moving!

Time to choose a shape to your hot rod (or rather not-rod)!

Trace a chassis on cardboard that's a little less wide than the straws you're using, and long enough for your fan and sail. Cut it out with scissors or an X-acto knife.

Hot glue on a raised support towards the front. This is where our motor will go so the fan doesn't hit the chassis when it spins. The support can be whatever you have lying around. In my case: blocks leftover from this project.

Looking good and immobile!

Throw on a healthy dose of hot glue on your motor, and stick it to your support.

Hook up the back of your motor with wires so that you can attach a battery. In my case, I used a 9V battery, which I glued on to the chassis. For the wiring, I used a 9V battery lead that snaps right on top. You can get these DC motors to run even with a single AA or AAA battery, so feel free to experiment with wiring hook-ups.

If you want, you can solder the wires on to the motor terminals, but be sure it is the case that your motor turns the right way for your fan blades. Otherwise, your car might accidentally go places!

I know, you do these projects for the fans. Well there are a couple options to choose from.

The first is to go with a pre-made propellor. These are not too hard to come by, you have lots of options, and they're quite powerful.

However, if you want to go all DIY on it, you can cut off the top of a plastic bottle to make a snazzy one, too. Leave some neck, and cut fan blades down the length of the plastic. Tilt the fan blades all the same way (making sure that with the way the motor turns, it will push air toward where the sail will be). Replace the cap, and poke a small hole for the axle of the DC motor to go through. Slide on with a little glue and you have your second fan. And you can make it YOUR BIGGEST FAN.

Test them out on your hand to make sure you're getting some good wind.

Let's add a catcher of the wind. Simply make a couple slits for craft sticks at the rear of your chassis, and add a paper sail. You can make it any shape or curvature you want, so long as it's catching some wind from your fan.

It seems so right, doesn't it? The fan blows air at the sail so surely it should go, right? right? RIGHT!? (sigh)

It's time to work on the car's underbelly.

Turn your chassis over, and glue the two straws so they are parallel and are oriented like an axle in a car would, from side to side. Next, slip your wooden dowel through and cut off any extra so that the dowel is just a bit longer than the straw. Repeat for the other straw.

You're wheel-y close!

Your car is going to need some stunning wheels. If it can't function, it might as well look good, right?

You can use any round object around (e.g. bottle caps, CDs, coins). I happened to have extra checks, so I drilled small holes in them as close to the center as I could so they could fit snugly on my wooden skewer axles. Once they're ready, snug them on so your car can roll.

Turn your fan on, and as the wind catches in the sails, watch as your car......goes nowhere.

Oh, no! Newton was right. For every action, there is an equal an opposite reaction. When the propellor turns on, it creates thrust forward by pushing air backwards. By catching the air in the sail, thrust is created in the opposite direction. If only our fan were more powerful, our car might split in two. But for now, it goes nowhere.

So how can you make the car go somewhere? Well that is the absolute best part. Because self-defeat can become self-success with the addition of nothing else but a piece of cardboard or paper. Place a sheet in between the propellor and the sail, and you've disentangled the two from their silly cycle. With the wind no longer hitting the sail, the thrust from the fan wins out and pushes the car forward. But don't just tell your students or friends that. Let them figure it out for themselves.

I'd love to hear your comments, questions, and thoughts below.

Have fun with it, modify it, mess with it, and as always, keep exploring.