For our first official experiment with the Lego Mindstorm NXT platform we used LabView to power the wheels and compare the distance it calculated to the distance we measured. For the most part LabViews calculations were close (10% error or under), with the average percent error being 8.07%.
You can read our measurements here, or in an excel spreadsheet attached below:
| Power Setting | Time(s) | Number of Turns | Left Wheel Rotation | Right Wheel Rotation | Velocity (m/s) | Distance Calculated (m) | Distance Measured(m) | Percent Error |
| 75.00 | 1.00 | 1.52 | 552.00 | 546.00 | 0.27 | 0.27 | 0.28 | 2.50 |
| 75.00 | 1.00 | 1.53 | 554.00 | 549.00 | 0.27 | 0.27 | 0.29 | 5.34 |
| 75.00 | 1.00 | 1.52 | 551.00 | 546.00 | 0.27 | 0.27 | 0.29 | 5.86 |
| 50.00 | 1.00 | 0.95 | 345.00 | 342.00 | 0.17 | 0.17 | 0.19 | 10.00 |
| 50.00 | 1.00 | 0.93 | 338.00 | 335.00 | 0.17 | 0.17 | 0.19 | 11.84 |
| 50.00 | 1.00 | 0.95 | 345.00 | 341.00 | 0.17 | 0.17 | 0.18 | 5.28 |
| 25.00 | 1.00 | 0.39 | 143.00 | 142.00 | 0.07 | 0.07 | 0.08 | 5.33 |
| 25.00 | 1.00 | 0.39 | 140.00 | 139.00 | 0.07 | 0.07 | 0.08 | 13.13 |
| 25.00 | 1.00 | 0.36 | 130.00 | 132.00 | 0.07 | 0.07 | 0.08 | 13.33 |
For easier reading: Lego NXT Post1
The difference between measured and the LabView’s calculated values are not spontaneous or without probable cause. The calculations done were based off of rounded values and used a circumference for the wheels that was estimated using a ruler, which has a fairly low accuracy.
Another problem that arose occurred before we started our measurements. It appeared that we couldn’t figure out how to properly assemble the the third wheel of the car. At first, the tire was rubbing against the body, thus causing it drag and slow movement. Upon adjustment, the wheel would not stay straight, thus turning the car even when both motors were evenly powered.
The last most likely source of error is the inconsistency in starting position during trials. While we attempted to keep the starting point consistent, it is unreasonable to expect a perfectly uniform system of measurement given the materials at hand.
NXT Side View
A fun experiment and neat introduction to LabView, though the assembly did become frustrating, but it will be interesting to see how else we use the NXT platform, and what other experiments lay ahead. I wish we had utilized a larger space rather than a desktop in class, but we made due with what we had.