Name of Activity Digital Measuring Wheel
Author STOMP
Keywords NXT, rotation, sensor, measurement, accuracy, diameter, circumference, pi, distance, conversion
Subject NXTs
Grade Level 4, 5, 6, 7, 8, 9+
Time 1 Hour Total
Brief Description Use an NXT and a rotation sensor to buld a digital measuring wheel. The device can be
pushed by hand on the ground or at a distance using a handle. Check the device’s
accuracy with a measuring tape.
Lesson Objectives: – To learn about programming in NXT MINDSTORMS.
– To use measurements and math in programming to collect data.
Materials Needed: NXT brick
NXT motor w/built in rotation sensor
LEGO wheel and axle
Computers running NXT-G MINSTORMS software.
USB cords to connect NXT bricks to computers
Data collection sheet
Preparation and Set Up:
– Arrange students in groups of two.

– Distribute necessary materials.
– Distribute a data collection sheet.

Necessary Background Measuring wheels are used in many places to find the distance of a line. The number of
rotations can be translated to distance if the circumference of the wheel is known.
The circumference can be found by measuring around a wheel or by multiplying the
diameter by pi.


  1. Have students build a measuring wheel device. Attach a wheel with an axle to a motor. Wire the motor to the NXT brick, but do not attach the motor to the NXT brick.
  2. Have students measure the wheel’s circumference to use when calculating distance.
    1. Option: You may also have the students find the circumference by measuring the diameter and multiplying the diameter by pi.
    2. Option: You may also discuss radius by having students multiply the radius by 2 x pi to get teh circumference
    3. Option: Have students find the circumference all three ways and compare answers.
  3. Have students program the NXT brick to display the distance traveled by doing the following:
    1. Divide the rotation degrees value by 360 to get the number of rotations traveled (or have the rotation sensor count in rotations) using the “Math” Block.
    2. Multiply that value by the circumference to get a distance value by using the “Math” block.
    3. Convert this distance value to a text value using a “Number to Text” block.
    4. Display the text value on the NXT screen using a “Display” block.
    5. You will need to enclose the program in a loop so that it is continuously displaying measurement data
  4. Check the accuracy of the device with a tape measure by having students measure the length of different lines.
  5. Discuss, as a class, reasons that the measurement may not be accurate. Does this always matter? How could you make the measurement more accurate?
  6. Discuss the different variables in this experiment.
    1. The independent variable is the number of rotations.
    2. The dependent variable is the measurement shown on the screen.
    3. Discuss as a class the relationship between these two variables.
    4. Option: draw a line graph of rotations v. acutal measurement (inches, cm, meters, etc.) that the NXT brick displays.
  7. Discuss where a measuring wheel might be useful and where it is not useful. What other tools can be used to measure distance?
Extensions or Modifications: Add a touch sensor to clear data to take a new measurement.
Use a touch sensor to trigger when measurements are displayed.
Add sound feedback when certain distances are reached.
Convert the device to a wench that measures the length of a string wrapped
around it
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