Combining Mechanisms





Overview

Students combine mechanisms made in Lesson 3.  They invent mechanisms with one input that controls two or more outputs. These mechanisms are the starting points for making cardboard tableaus that are mechanically animated to tell a story: MechAnimations.

Materials

  • Two pegboard mechanisms with one input and one output.
  • Pegboard mechanism with one input and two outputs. Here are suggestions for making these three
  • Large drawing of a mechanism with one input and one output.
  • Pegboard base, four links and six pivots per student.
  • Worksheet: What will Each Output Do?

 



Procedure

Make a diagram of the mechanism you made. Make the diagram clear enough that someone else could use it to reconstruct the mechanism.

1.      Class meeting: Demonstrate two pegboard mechanisms with one input and one output as in the video above. Hold these two together and grasping both inputs, operate the two mechanisms together.  Then demonstrate one mechanism one input and two outputs that is a combination of the previous two. Discuss similarities and differences with mechanisms students have made.

Then present a large drawing of a mechanism with one input and one output. This video shows one way to do this.  

Present the design challenge to the class:

Make a pegboard mechanism where one input drives two or more outputs

2.      Students work on design challenge:  Here are some suggestions for students who may be stuck:

  • Make a mechanism like you did where one strip controls another strip.
  • Place another link where you would like a second output. 
  • How will you connect the second output to the input?
  • Does the second output need any other fastener?
         Some students have difficulty drawing the mechanisms they have made. Here are videos on drawing one output and on drawing a second output.

Science Notebook


  • Make a diagram of the mechanism you made. Make the diagram clear enough that someone else could use it to reconstruct the mechanism.
  • Place arrows on your diagram to show how the input makes the outputs move.
  • Explain in words how your mechanism works.

3.      Class Discussion: Ask two or three students to present the mechanisms they have made. Before they operate their mechanisms, ask others to predict how each part of the mechanism will move, and why.  Place post-its on the outputs of one of the mechanisms and ask:

  • What story could you tell with this mechanism? 
  • What pictures might you put on the post-its and on the base? 

4.     Homework: Worksheet: What will Each Output Do?

Outcomes

  • Each student constructs a pegboard mechanism with one input and two outputs.
  • Each student makes a diagram of the mechanism, using different symbols for the fixed and floating pivots, and indicating the directions of movement of its parts.
  • Students can predict the direction of movement of the outputs on a mechanism that is new to them.

Extensions 

One way to extend the work of students who finish early is to provide more specificity in the challenge. Suggest that a student make a mechanism with:

  • Two outputs moving in the same direction.
  • Two outputs moving in opposite directions.
  • One output moving a greater distance than the other output.
  • Outputs on two adjacent sides of the base.
  • Outputs on opposite sides of the base.
  • More than two outputs.

 



Worksheet

What will Each Output Do.doc
Download



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