Robo Arm


  • 1

    Here are some of the materials you can use

    • hole punch
    • 2 large paper clips
    • marker
    • 1 medium brass fastener (1 in. [2.5 cm])
    • paper cup
    • smooth string (39 in. [100 cm]) (for example, fishing line)
    • 1 straw (cut into 1-in. [2.5-cm] lengths) 
    • 1 strip of corrugated cardboard (about 2 x 4 in. [5 x 10 cm]) (corrugated cardboard has grooves in the middle, like a cardboard shipping box)
    • 1 strip of corrugated cardboard (about 2 x 8 in. [5 x 20 cm]) 
    • tape
  • 2

    Prepare ahead of time

    • Cut the cardboard strips. Cut the length of the strips along the corrugations (grooves) so the cardboard won’t bend easily.
    • Punch a hole in one corner of each strip. (You may need to get an adult to help with this step.)
    • Cut straw lengths to make guides for the string to slide through.
    • Unbend a paperclip to form a hook. Tape it to the inside of the cup.
  • 3

    Think about the challenge

    • What are some reasons robotic arms might be used? (Mechanical arms can be stronger and more adaptable than human arms; robotic arms can be remotely operated—from over millions of miles away!)
    • How is a robotic arm like a human arm?
    • How does your arm move when you pick up a cup from the table? How does your hand move?
    • TIP: Basing a design on an existing object is called reverse engineering. Making a Robo Arm is an example of reverse engineering because you are starting with something familiar (your hands and arms) and building a mechanical version.
    • TIP: Inventors are always looking for ways to improve things or meet people’s needs to help them improve their lifestyles.
  • 4

    Think about and write down your ideas

    • How many parts will your robotic arm have?
    • Think about how a robotic arm can pick up an object. How does it grab the object?
    • Think about how your arm bends and how you might make your robotic arm bend.
    • TIP: Inventors’ and engineers’ first ideas rarely solve a problem. When they solve a problem, they try different ideas, learn from mistakes, and try again. If things don’t work out, it’s an opportunity—not a mistake! This is all part of the design process.
  • 5

    Look at the materials

    • What materials can be used to make the “muscles”?
    • What materials can be used to make the “bones”? 
    • How will you make the arm bend?
    • What can you use to grab the cup?
    • TIP: Both human and robotic arms have flexible parts (muscle; string) that move rigid parts (bone; cardboard). The muscles’ pull is directed by a guide (tendons; straw). The joint (brass fastener) is the point where the arm sections are connected.
  • 6

    Design and build a two-section arm

    • Decide how you will connect the cardboard strips (arm sections) so they move freely.
    • Sketch or lay out the different materials in the order that you will assemble them.
    • Connect the arm sections. 
    • TIP: A Robo Arm is a lever system. The brass fastener is the fulcrum (the point where the lever rests and pivots) and the cardboard is the lever arm.
    • TIP: If your arm strips do not move freely, try loosening the brass fastener to reduce friction (the action of one surface rubbing against another).
  • 7

    Plan the string (muscles) path

    • Decide where you will attach the string (muscles) to the cardboard (bones) to make the arm move. 
    • Lay the string along the cardboard. 
    • TIP: Different attachment points for the string will give you different results—changes will alter the force required to move the lever and the distance the arm moves. 
  • 8

    Plan and attach the straw guides (tendons)

    • Decide how you will use the straws (tendons) as guides for the string.
    • Lay the guides on the cardboard where you think they should go and then review your placement choices.
    • Tape the guides in place.
    • TIP: The string’s (muscle’s) pull is directed by a straw guide (tendon). The position of each guide will affect the arm’s efficiency. 
  • 9

    Connect the string (muscles)

    • Thread the string through the straw guides.
    • Position and tape the string end to the hand section.
  • 10

    Test your Robo Arm

    • Pull the string to make your hand move.
    • TIP: If the hand doesn’t move in the direction it should, check where you taped the end of the string to the cardboard. You might also check that the guides make the string pull in the right direction.
  • 11

    Add a hook to your Robo Arm

    • Unbend a paperclip to form a hook.
    • Poke the straight end into a groove in the cardboard at the end of the hand.
    • Secure the hook with tape.
  • 12

    Move your arm and lift the target cup

    • Position the paper cup on the table.
    • Move the arm toward the target.
    • Hook the target and lift!
  • 13

    Did you know?

    • NASA Explores Space
      The International Space Station has a robotic arm. It is 58 feet (18 m) when fully extended and weighs 4,000 pounds (1800 kg). It moves equipment and supplies around the station, supports astronauts working in space, and services things like instruments. Because robotic arms are so versatile, many spacecraft use them, but most are much smaller than the one on the space station.

      The Phoenix spacecraft reached Mars in 2008. It has a 7.7-foot (2.4-m) robotic arm that dug into the soil to uncover a layer of ice. The arm dropped soil samples into instruments that checked for water and carbon-based chemicals—things that are needed to support life. 


  • 14

    Try this next!

    • Make a full arm. Add a third section to your Robo Arm so it has three parts like a person’s arm––upper arm, lower arm, and hand.
    • Pick it up! Modify your arm so your hand can grip and pick up an object.