Self-Defeating Fan Car




About: I made a book with some new projects in it! It's called Marvelous Makeable Monsters. Check it out here: The Oakland Toy Lab is a community-based wonder lab for students to build, ti...

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!

Step 1: Make a Car Chassis

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!

Step 2: Mount Electronics

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!

Step 3: The Fan: Two Options!

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.

Step 4: Host the Sail!

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)

Step 5: Straws and Axles

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!

Step 6: Wheel Up

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.

Step 7: Self-Defeating Car Vs. Self-Successful Car

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.



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    25 Discussions


    1 year ago

    My dad made a removable sail so when you turn on the fan, you take off the sail and the car will move. I'm doing this for my STEAM project and I thought that it would be good. It ruins the fan car.


    1 year ago

    I don't understand the reasoning for making one. could someone explain

    1 reply

    2 years ago



    3 years ago

    Words. They make pictures in your head called imagination. There's your video.

    1 reply

    3 years ago

    If the fan was REALLY powerful, It could it could make the car fall backwards right? (Or [not] split in to two pieces, Like you said)

    1 reply

    Reply 3 years ago

    Then the resistance made by the other piece would be just as strong, it's a "fun" trick question on any Physics 101 class, referring to the third law of physics, for every action there is a reaction equal in strength but opposite to the first. So as the wind pushes towards one direction, the "sail" will push on to the opposite with the same amount of force, canceling any movement.

    mozkowizobeh kok siang

    Reply 3 years ago

    No, It just wouldn't do much, the fan is designed to push air making it go the other way wouldn't make much but make the pieces of plastic that make the fan curl up.

    Yonatan24Dawn Chang

    Reply 3 years ago

    Did you read the title of this Instructable...?


    3 years ago

    Mythbusters proved you wrong :)


    3 years ago

    Awesome. I helped my son (just turned 7 years) make a small electric car similar to this last weekend (used a rubber band as belt drive onto one of the wheels). This project will make a perfect 'Next Step' in his EV education. Thanks :)


    3 years ago

    Thanks for the science and the laugh.


    3 years ago

    I love all of the cheesy puns! I saw something like this in an old MAD Magazine but full sized and with a leaf blower.

    1 reply