1. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Wheel Size Matters: Programmed Rotations Introduction: An Investigation into the effect that changing wheel size has on the distance traveled.

2. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Investigation Hypothesis: If the number of rotations of the motor axes is held constant, then a larger diameter wheel will move the vehicle a proportionately greater distance. Variables: –Independent: Wheel size (3 diameters) –Dependent: Distance traveled.

3. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Practical Applications Prepares the student to understand gears and ratios Helps in design of robots, especially where speed is an important factor.

4. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Prepare Test Bed Prepare the test bed (including a starting line taped to the board).

5. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Modify the Squarebot Modify the Squarebot as shown in the Helper Section at the end of Teacher’s Notes document.

6. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Prepare the Program 1. Open ROBOTC. Go to File/Open Sample Program. 2. Open Encoder. 3. Open vex_line_track_rotations. c Download the program to the Squarebot

7. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 1 Position the Squarebot Place the rear frame of the modified Squarebot against the test bed boundary, with the small front wheels on the starting line.

8. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 2 Run the Robot Run the vehicle by turning the controller off, then on.

9. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 3 Mark Stopping Point When the MOTOR STOPS RUNNING mark the location of the front end of Squarebot as closely as possible. This may be accomplished by dropping a ruler at the estimated spot (Fig. 1), then marking the board as shown in Figure 2.

10. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 4 Measure Distances Measure the distance from the starting line to the spot where the front of the Squarebot stopped.

11. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 5 Record Data Record this distance on a data table of Wheel Size vs. Distance Traveled CONDITION (Wheel Size) TRIALS (inches) 12345Average 1 (Small)44 ½42 ¼43 ½42 ¾41 ½ 2 (Medium)111111 3 (Large)111111

12. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 6 Gather More Data Repeat the procedure at least two more times to insure that your measurements are accurate

13. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 7 Average Values Find the average of the trials for the condition and record it on the table. Example:

14. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 8 Medium Wheels Switch to medium sized wheels and repeat the steps #1-7 with the new wheels.

15. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 9 Largest Wheels Switch to the large wheels and repeat in the same manner as the other sized wheels.

16. Copyright Carnegie Mellon Robotics Academy all rights reserved Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. Step 10 Plot Diameter vs. Distance The plot is a powerful visual demonstration leading to a clear conclusion As wheel size increases, distance traveled increases proportionally.