NXT Robots

We built a robot vehicle using the LEGO NXT Robot kit. Our vehicle has three wheels. There is one wheel in the rear that is not connected to a motor. There are two wheels at the front which are each connected to their own, independent motors. At the center of our vehicle is the NXT brick, which is used to translate the programs we design on the computer into tasks for each motor to perform. Using the software we can control the speed of each wheel, as well as the length of time it will move. Once the program has been designed, we can download it into the brick, and unplug the vehicle from the computer. Then we can place the robot in an open space with room to fulfill the programmed task. We can also stop the vehicle at any time by pressing the orange button on the brick.

Our first challenge was to create a program that would cause the robot to drive in a circle with a 2 foot diameter. To achieve this, we gave each wheel separate commands. One wheel was given a speed of 100, the other a speed of 50. Since one wheel was moving much faster speed, and since both wheel were consistent, the vehicle drove in a circular shape. We then adjusted the speeds several times until the vehicle successfully performed the (approximate) two foot diameter circle at the highest speed possible.

For our next challenge we programmed the vehicle to move forward in a straight line for exactly one second. We used a ruler to mark the starting position of one tire, then measured the distance it traveled. We measured this distance to be 26.7 cm. We then used the program to look up the exact distance travelled, or the distance that was supposed to be travelled. This was 26.4 cm. There was a 3 mm difference in measurements. We then figured out the percentage error. To do this we followed a simple formula. First we found the difference between our measurement and the actual measurement; This was .3 cm. We then divided .3 cm by the average of the two measurements, which was 26.55 cm. The percentage error we calculated was 1.13%. A percentage error this small was undoubtedly caused by human error. First of all, we could have simply measured incorrectly. Perhaps we marked the table slightly in front of, or behind, the exact place the where the wheel was resting at the beginning or end. We my also have placed the ruler too far forward when measuring the resting place. Another possibility is that the vehicle did not actually travel the distance it was supposed to. This may have been caused by the cords hanging off the back of the vehicle causing drag. It is possible that the drag from the cords caused the tires to spin just enough to set the vehicle back a few millimeters. It was almost certainly one of if not both of these possible errors that caused our slight difference in measurement.