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Materials (per person)
- 4 brass fasteners
- corrugated cardboard
- hole punch
- objects to pick up (e.g., tennis balls, cotton balls, plastic soda bottles, and paper cups)
- 2 rubber bands
- tape (duct or masking)
- 4 toothpicks
- 4 wooden skewers
- yardstick (or long paint stirrers for 5-gallon buckets, a thin wooden slat, or lath 2–3 feet long)
Design and build a device that lets you grab different objects and drop them into a container that's at least two feet away from you.
Brainstorm & Design
Look at your Materials and think about the questions below. Then sketch your ideas on a piece of paper or in your design notebook.
- Using these Materials, what can you build to grab objects that are two feet away from you?
- How will your grabbing device open and close so it can grip an object and let it go?
- How will you attach your grabber to the end of the stick?
- How will you control your grabber when it's at the end of the stick?
Build, Test, Evaluate & Redesign
Use the Materials to build your grabber. Then test it by trying to pick up different objects. When you test, your design may not work as planned. When engineers solve a problem, their first solution is rarely their best. Instead, they try different ideas, learn from mistakes, and try again. Study the problems and then redesign. For example, if your grabber's jaws:
- have a weak gripIncrease their force. Each arm of the jaw is a levera bar that pivots around a fulcrum. In this case, the fulcrum is the brass fastener. Change the strength of your jaw's grip by adjusting the length of the arms and the fulcrum's position. (See illustration.)
- keep dropping thingsMake sure that the jaws close enough to actually hold something. Also see if the jaw's gripping surface is big enough and shaped right to have a firm grip.
- bend or twistReinforce them with something stiff. Also, check if the jaw's arms are longer than necessaryshort arms don't bend as easily as long ones.
- don't work at the end of the stickMake sure the string, rubber bands, and moving parts aren't getting stuck. Also, move the jaws with your hands. If they don't work the way they should, readjust the parts.