Our First Lego Mindstorm Activity

 

After watching each installment of Michael Bay’s box office hit, I found the true origins of America’s favorite robots. No the Transformers aren’t from Cybertron but from the bottom of a box of Legos and constructed by students like me and my classmates. Well not really, but the drama of that is so much more exciting.
Anyhow, this is the first of our activities and in it we set out to study the motion of our newly constructed robots as well as the measurements of distance and power. We calculated our results using a few key formulas. The set of formulas we used formed a Jenga tower. Each piece supported another and if you miscalculated one thing the whole came crashing down and you had to start all over.
First we started with measuring diameter of the robot’s tires in order to calculate circumference. We measured using a standard and converted from inches to centimeters to meters.
Here’s the conversion equations:
cm = in • 2.54
m = cm/100
The diameter of the tires equaled 0.0508 m. From this we calculated circumference using this equation: circumference = π • diameter or   C = πd. From this we calculated that C=0.1596. This is the number we input into the computer program for Lego Mindstorm.
We powered on our robots to begin and the math still wasn’t over. With the circumference we needed to figure out number the of wheel turns. For this we had another equation:
Number of Wheel Turns = (rotation°) / (360°/1 Turn)
Then both wheel turns and circumference were used to calculate the distance our robot travelled:
Distance (meters) = Number of Wheel Turns • Circumference
Distance was entered into yet another equation to find velocity:
Velocity = Distance (meters) / Time (seconds)
It all seems very mathematical, and it is, but most of the information could be inputted into the program and was automatically calculated; we recorded the given information.
To begin the actual experiment, we cleared a pathway for the robot to travel without any obstructions (like its power cord which kept getting in the way) and adjusted the power so that the distance would not exceed the measurement of our ruler, 12 inches or 30.48 centimeters or 0.3048 meters.
We conducted a trial of one power level (75) and three sets of testing for increased accuracy. We found that our measurements of distance we never the same and always greater than those measured by the computer. This could be due to eyeballing exact distances when they fell between the marked lines of the ruler. I’ll list our measurements or distance (D) and velocity*(V) compared to those of the computer in addition to number of wheel turns (WT).
*Because in our tests we set time (seconds) = 1, velocity and distance are equivalent in number
Test 1
Students                                  Computer
D = 0.27305                            D = 0.227873
V = 0.27305                            V = 0.227873
WT = 1.42778
Test 2
Students                                  Computer
D = 0.2795                              D = 0.24605
V = 0.2795                              V = 0.24605
WT = 1.54167
Test 3
Students                                  Computer
D = 0.27432                            D = 0.246493
V = 0.27432                            V = 0.246493
WT = 1.54444
At the end of our trial set we were to calculate our margin of error in order to measure how applicable our results would be on the grand scale. A high margin of error means results are less accurate/applicable and a low margin of error means results are more accurate/applicable. To measure this we used this equation:
% Error = ( (Distance measured – Distance calculated by computer) / ((Distance measured + Distance calculated by computer) / (2) ) •100%
The margin of error for each test is detailed below.
Test 1
% Error =  ( (0.27305 – 0.227873) / ( (0.27305 + 0.227873) / 2) ) •100%
% Error =  ( (0.045177) / ( (0.0500923 / 2) )  • 100%
% Error = ( (0.045177) / (0.2504615) ) • 100%
% Error = 0.18037503 • 100% = 18.04%
Test 2
% Error = ( (0.2795 – 0.24605) / ( (0.2795 + 0.24605) / 2) )  • 100%
% Error = ( (0.03345) / ( (0.52555 / 2) ) • 100%
% Error = ( (0.03345) / (0.262775) )  •100%
% Error = 0.12729521 •100% = 12.73%
Test 3
% Error = ( (0.27432  – 0.246493) / ( (0.27432 + 0.246493) / 2) )  •100%
% Error = ( (0.027827) / ( (0.520813) / 2) ) • 100%
% Error = ( (0.027827) / (0.2604065) ) • 100%
% Error = 0.10685985 •100% = 10.69%
The average for the % error for all three tests is as follows:
Average % Error = (% Error Test 1 + % Error Test 2 + % Error Test 3) / (Total Number of Tests)
Average % Error = (18.04% + 12.73% + 10.69%) / 3
Average % Error = (41.46%) / 3 = 13.82%
Given the small sample size of our testing, I think our margin of error is reasonable though next time we can do more to improve our measuring accuracy.
That’s all for this Lego Mindstorm experiment. Until next time!