1. Introductory Presentation
Wheels and Distance
Introductory Presentation

2. Forward Motion Built-in Rotation Sensor
The Interactive Servo Motors all have a built-in Rotation
Sensor. The rotational feedback allows the NXT to control
movements very precisely. The built-in Rotation Sensor
measures the Motor rotations in degrees (accuracy of +/- one
degree) or full rotations. One rotation is 360 degrees, so if
you set the Motor to turn 180 degrees, the hub will make half
a turn.

3. Rotation Sensor
Test the Rotation Sensor’s ability to measure distance.
Connect the Motor to the NXT.
Select View in the NXT display.

4. Duration

5. Forward Motion In this program:
1. How far did your robot move forward?
2. What affected the distance it moved?
3. How could you get it to move a longer distance?
A shorter distance? An exact distance you want?

6. Many things affected how far your robot traveled.
Forward Motion
Many things affected how far your robot traveled.
The number of degrees your Wait For block is set to wait for
The size of your tires

7. Wheels and Distance
In this activity we’re going to program our robot to move an exact distance.
To do so we must understand a few things about circles.
START
FINISH

8. Review Let’s start with the basics. Answer the following:
The distance from the center to the outside of a circle. r
1. What is a radius of a circle?
2. What is a diameter of a circle?
3. What is the formula for the circumference of a circle?
The distance, through a circle’s center, from one edge to another. d
Circumference= diameter * π

9. Preview
With our knowledge of circumference, we can start figuring out how to control the distance our robot goes.

10. Preview
First, we need to understand that the circumference of a circle is really just a line curled around a center point.

11. Review
From this, we know that the circumference of a circle and the length of the line it rolls out are equal in length. Finish the following:
d = 4
Circumference = 4 * π
So we know that…
Length of Line =
4 * π

12. Let’s try a few more. Finish this chart:
Preview
Let’s try a few more. Finish this chart:
Circumference =
Length of line =
1 meter
1 meter
2 meters
2 meters
7 meters
7 meters

13. Once you have completed the activity check your prediction
Preview
Predict what would happen if we were to change the number of rotations that the wheel makes? Or change the diameter of the wheel?
Once you have completed the activity check your prediction

14. There are 360˚ in one full rotation of a wheel
Review: Degrees
360˚ 0˚
270˚
90˚
180˚
There are 360˚ in one full rotation of a wheel

15. Circumference: Distance Traveled
Wheel Diameter: cm
Circumference = 5.75 cm x 3.14
Circumference = 18 cm
1 cm = 10 mm
18cm = 180 mm

16. Method 1: Calculation

17. Method 2:
Measure Degrees