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Lab1Group3Question4

To the group page --> SuperStars

Drive Command: Group - Superstars - Thinh Vu

Hypothesis

The drive command measures radius from the center of the CreateBot to the center of the circle created. The velocity is measured as the average distance over time of both wheels.

:Materials: IRobot Create
RealTerm Program
Windows Operating System
Large Sheets of Paper
Tape
Colorful Markers
Connector
String
Ruler
Protractor
Circle Measurement Device
Stopwatch
TI-89 Calculator

Procedure

1. First, laid out a piece of paper.
2. Taped two different color markers on both the left side and right side of the Create.
3. Turned the Create on, inputted 128 131 for open interface and safe mode.
4. Inputted the code for drive with a designated radius at 100mm/s. (ex. 137 0 100 0 200)
5. With a stopwatch, measured how long it took the Create to complete its circle. Then used 137 0 0 0 0 to stop.
6. Compared the time it took to complete the circle and the supposed time. (found by the circumference/inputted velocity) 7. Using the circle measurement device, created two tangent lines on the bigger circle.
8. Used perpendicular lines to find the center of the circle.
9. Tied a piece of string to a different colored marker.
10. Measured out the string to the inputted radius and marked it on the string. With finger on mark and center of circle, created a circle with the inputted radius.
11. Measured the distance between the two other circles with the circle just created.
12. Repeated with other radii measurements.

Results/Data

Various trials using 100mm/s as velocity. The trials are defined by the inputted radii.

Velocity Table

Radius Table

Ri: Radius of the Circle Made By the Inner Side
Ro: Radius of the Circle Made By the Outer Side
Ra: Radius of the Circle with the Inputted Radius

Figure R.1

Observations/Conclusions

When measuring the radius of the drive command, it proved fairly accurate. The experiment used one marker on both sides of the Create. After the two circles were drawn, a third circle was drawn by hand in accordance with the actual inputted radius. The distance between the inner circle and the handdrawn circle was very similar to the distance between the outer circle and the handdrawn circle as well. Also, when looking at all three circles at a birds-eye view, you could clearly see that the circle with the inputted radius clearly ran through the center of the Create. Any error was most likely due to human error, such as a shaky marker or hard to see lines. All in all, the radius does measure from the center of the Create to the center of the circle made.

The velocity on the other hand was much more strange. The experiment was done to see how long it would take the robot to draw a circle. The time taken by the stopwatch was compared to a calculated time found by the distance/velocity (in this case, distance was the circumference of the circle made). Although there is possible human error in using the stopwatch, it is not enough to make such large errors in the velocity. It seems that the velocity became more accurate as the distance increased, which makes it seem as though there is some delay possibly due to processing. It could also be acceleration, but the same problem does not occur for the drive direct command. Therefore, there must be some type of constant inaccurate behavior in the Create when using velocity in the drive command. A conclusion could be that the left or right wheel in the drive command move at faster or slower pace, amd the error would mean less as the distance grew. That would explain the more accurate velocity for greater distances. Nonetheless, this experiment requires more work to find out what the error is in the velocity. My conclusion would be that velocity is still measured by distance over time but there is some in built behavior in the Create that causes it not to be exact.