Institute of ImaginationRobot LabRobot Lab
Build a body

Make it roll!

Give a small box four bottle cap wheels on skewer axles, and pull it along on a string.

  • About 40 minutes
  • 7 steps
Step by step

One step at a time, in big writing.

A box on two wheels pulled along by a string, with a card strip from the back wheel making a shape on the box wave

Before you start

What you need

Tools

To print

Materials

Make it

The steps

How it works

Each wheel is fixed tight on a stick called an axle, so they turn together. The axle spins freely inside a straw. Weight over the back wheels presses them onto the floor, so they turn instead of skidding.

Side view of the box on two bottle cap wheels with a string pulled to the right. A curved arrow in each wheel shows the wheel and its axle turning together while the box rides level on top.

  1. The underside of a box, with one straw taped across it near the front and one near the back; each straw is a little shorter than the box is wide

    Tape on the straws

    Cut two straws a little shorter than your box is wide. Tape one across the underside of the box near the front and one near the back, with tape at each end. Keep the straws parallel.

  2. The underside of the box with a skewer pushed through each taped straw, its ends sticking out past both sides of the box. A curved arrow at the end of each skewer shows it spinning freely inside the straw.

    Push in the axles

    Push a skewer through each straw, with the same length sticking out on each side. Spin each skewer. Does it turn freely?

  3. Front view of a box on wheels: a straw taped under the box, a skewer through the straw, and a bottle cap wheel fixed on each end of the skewer

    Fix the wheels

    Push a bottle cap onto each skewer end, open side in. Leave a finger's width between cap and straw. Spin a wheel. Do the wheel and axle turn together?

  4. A twisted elastic band, then a bottle cap wheel seen from the side, with the band looped twice round its rim

    Put on the tyres

    Twist an elastic band into a figure of eight and loop it twice round each cap, so it sits tight and grips.

  5. Cut-away side view of the box with its end flap open and a lump of Blu Tack inside, right over the back axle. One arrow presses the lump down, and a second arrow shows the back wheel pressed onto the floor; the front wheel has no weight over it.

    Add some weight

    Open an end flap, press the Blu Tack or plasticine inside right over the back axle, and close the flap.

  6. Side view of the box on two bottle cap wheels on the floor, with a piece of string taped to the front and pulled to the right; a curved arrow in each wheel shows it turning

    Pull it along

    Tape the string to the front of the box. Pull it slowly along the floor. Do the wheels turn?

  7. Side view of a box on two wheels pulled by a string; a split pin through the back wheel, away from the middle, pushes a card strip that makes a shape on the box wave

    Invent your own

    Decorate your box as a vehicle, creature or robot. What could you fix to a wheel or axle, so something moves as it rolls?

After the steps

Use it on your robot

Tape straws under your robot's body and add axles and wheels, so it rolls when you pull its string.

Your turn

Ideas to try

Make something else

  • A robot on wheelswith a paper cup head and skewer arms.
  • A trainof boxes tied together with string.
  • A creature on wheelswith a paper tail that spins.

Then change something

  1. Push a paper propeller onto the front axle. What does it do as the box rolls?
  2. Swap a back cap for a card wheel. Pin a card strip to it, away from the middle, and to a paper arm pinned on the box. What does the arm do as you pull?
  3. Put bigger wheels at the back. How does it roll now?
  4. Move the weight to the front. Does it still roll?

iOi challenge

Make a robot on wheels that carries a passenger 2m without it falling off.

More to make