Instructional Material: EV3 - Under Construction The Captain's Burried Treasure

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The Captain's Buried Treasure, Part I (pdf file)

Students are required to use precision swing turns to end up where "X" marks the stop. The combination of two obtuse angle turns and three straight stretches provides a good lesson on dead-reckoning navigation (using time or rotations to control movement - no sensors). Some key learning to watch for:

  • Have students begin to break large tasks into smaller individual behaviors to make them more manageable
    • Lay the ground work for the future Flow Chart lesson
  • Reinforce the importance of adding comments to their programs as an organization tool
  • Ensure students are using the prescribed swing turn and understand is implementation details
  • Repeatability is a struggle with plastic robots. Factors which effect repeatability include:
    • Initial alignment of the castering wheel
    • Initial orientation of tribot - x,y position and rotation
    • Slack in drive train (motors, gears wheels)
    • Wheel alignment
    • Wheel balance (wobble)
    • Structural rigidity
    • Uneven friction
    • Mismatched motors
    • Battery level
    • Motor control (Move & Motor Blocks)
  • Probe how students developed the parameters for their Move Blocks
    • Guess-and-check
    • Proportions (figure out distance of one rotation and scale for others, etc.)
    • Rotation sensor feedback (use view mode or Move Block feedback panel while physically move the tribot the desired distance - without wheels slipping - and recording the reading for use as the Move Block Duration parameter)
  • Discuss why this challenge was so difficult (tedious) and introduce the idea dead-reckoning for navigation versus using sensors to help determine position during navigation. With dead-reckoning, you only know your position at the very beginning and each error or variation compounds on the previous errors or variations.
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