Parents, Educators & Engineers

Heavy Lifting

Materials (per crane)

  • cardboard box (shoebox size or bigger)
  • 3 strips of corrugated cardboard (2 x 11 inches/5 x 28 cm)
  • paper clip
  • large paper cup
  • 3 sharpened pencils
  • scissors
  • smooth string (e.g., fishing line or kite string)
  • tape
  • weights (e.g., batteries, pennies, marbles, or gravel)

We Challenge You To...

... design and build a crane and see how heavy a load it can lift.

Brainstorm and Design

Think about things that might affect how heavy a load your crane can lift.

  • How will you keep the crane's arm from breaking off the box as it lifts a load?
  • How will you stop a heavy load from pulling the arm to the left or right?
  • How will you wind and unwind the cable so the hook can go up and down?


  1. First, make the arm. The arm holds the string up and away from the crane's body. Use one, two, or all three cardboard strips to design your arm. Then attach it to the box.
  2. Next, make a take-up reel. Figure out how to make a take-up reel that lets you shorten and lengthen the cable. (Optional: add a crank to turn the take-up reel.)
  3. Finally, add the string, hook, and cup. Run the string through the arm. Attach it to the take-up reel and hook. Poke holes in each side of the cup near the rim. Make a handle for the cup and slip it onto the hook.

Test, Evaluate, and Redesign

Ready to test? Add weight to the cup. What's your crane's breaking point? Engineers improve their designs by testing them. The steps they follow are called the design process. Try some ideas and build an improved version. If:

  • the load rips the arm off the box—Reinforce how it attaches. Add cardboard supports. Or cut slits in the box to hold the arm. Also, add tape to the top and underside of the box.
  • the arm crumples—Start over with new cardboard. Also, use several pieces of cardboard for an arm, either all together or spaced apart.
  • the load pulls the arm to the side—Use extra cardboard or string to add support.
  • the crank handle bends or slips—If it slips, tape it or attach it more firmly. If it bends, reinforce it.
Heavy Lifting picture