Instruction Guide: How Far?

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NOTE: This lessons assumes students have access to wheels beyond those available in the base kit.  The challenges can be modified to use only the stock wheels.

This explicit math lesson takes the concepts learned in Moving Straight and ties in Middle School Math Standards on measuring diameter, calculating circumference and proportional math.

Students should use the How Far? Task Assignment sheet to complete this exploration.

Walk students through the How Far? PowerPoint under Student Resources:

Slide 1

  • Students need to understand the concept that the distance the robot will travel in one rotation of the motor (the orange hub) is equal to the circumference of the wheel attached to the motor. Some students may not know the term "circumference", but with their robot in hand, help them visualize that in one rotation of the motor the robot travels the perimeter of the wheel one time.
  • Explain to students that the circumference is tricky to measure directly (let them try if you like), so we use the formula: Circumference = Diameter X Pi, since the Diameter is easier to measure. Again, you may find it necessary to review or explain both Diameter and Pi.
  • This slide also lays out three challenges:
    • A) This challenge has students write a program to have their tribot move forward 720 degrees. The students must calculate how far they expect their robot to travel in this program, measure and mark this distance on the board, and then test it with their "Lego-dude" standing just beyond the calculated line.
    • B) This challenge requires students to calculate the number of rotations their tribot will require to travel 50cm, based on the wheel size in their bot. In this case they use a predrawn line already on the board and "Lego-dude" stands on the 50cm line during the test.
    • C) This challenge is similar to B), but using English measurements with a predrawn 25in line.

Slide 2

  • This slide is a template for the first 2 steps in solving any of the three challenges:
    • Step 1 - Measure the diameter of the wheel. Make sure students measure through the center of the wheel and in the appropriate units.
      • Note: for Challenge C, students will need to measure the diameter in fractions of an inch (16ths should be sufficient), but they will then need to convert this fraction to a decimal before multiplying bu pi in the next step.
    • Step 2 - Students multiply the measured diameter by pi to get the circumference.

Slide 3

  • This slide is the final 2 steps for Challenge A:
    • Student show that 720 degrees is 2 rotations of the wheel, so they multiply the answers from Step 2 by 2 to get the predicted distance.
    • Students should then measure this distance from the starting line, mark it on the horizontal whiteboard. After placing the Lego-dude behind the drawn line, they should run their 720 Degree program and have the robot stop just short of the Lego-dude.
      • Note: the students need to place the entire robot behind the starting line.

Slide 4

  • This slide is the final 2 steps for Challenge B:
    • Student divide 50cm by the calculate circumference to determine the number of rotation required in their program.
    • After creating and downloading the program, students place their Lego-dude behind the predrawn 50cm line and run their program with the entire robot behind the starting line.

Slide 5

  • This slide is the final 2 steps for Challenge C:
    • Student divide 25in by the calculate circumference to determine the number of rotation required in their program.
    • After creating and downloading the program, students place their Lego-dude behind the predrawn 25in line and run their program with the entire robot behind the starting line.

Have students complete the Task Assignment using the above slides as a model for their calculations.