Design Notebook
11-7-04
Our water balloon launcher incorporates a catapult design powered by surgical tubing that is somewhat simplified so that a third grader could operate it. Our test plan is two-fold. The first tests will be conducted as we assemble the launcher. Once it is built, we will measure out a distance of 20 meters and place a marker there. Then, we will launch five balloons, and depending on where they land, we will make some small adjustments to the tubing length or angle of release. We will repeat this process as many times as is necessary After the launcher is adjusted to our initial specifications, we will allow a third grader to operate it, and if he cannot, we will make any necessary adjustments until he can operate it.
First Attempt:
Mean : 9 meters Std. Deviation: 2.5
After this attempt, it was determined that the release angle was to horizontal, so it was adjusted to be more towards the ideal angle of 45 degrees.
Second Attempt:
Mean: 11 meters Std. Deviation: 3.0
After this attempt, we determined that the cause of the problem might not be the launch angle but the force generated by the launcher, so the surgical tubing was tightened.
Third Attempt:
Mean: 14 meters Std. Deviation: 2.5
After this attempt, we realized that we had the maximum force that could be generated by a single layer of tubing, so we took the excess tubing and created a double layer of tubing, two bands on each side. When we started to test this design, we observed that this new strength put too much tension on our center support piece. After a little brainstorming, we decided to move the tubing down the support near the center, so that it was not as stressed, this would also reduce instability and “whip.”
Fourth Attempt
Mean: 12 meters Std. Deviation: 18.0
This data is somewhat skewed because one of the balloons blew up in the launcher when it was launched, so we made no adjustments and tried again.
Fifth Attempt
Mean: 18 meters Std. Deviation: 2.0
This data is acceptable to us and we made no further adjustments because two of the balloons hit the mark, two fell slightly before the mark, and a fluke landed very much short of our goal, but we are content with these results.
Third Grader Test
The subject of these tests was my cousin Joey, who is currently 8 years old. Under the supervision of his parents, and after a brief instructional session, Joey was more than able to operate the launcher on his own. More importantly, he thought the appearance of the launcher was “cool” and asked if he could keep it. Unfortunately we told him that he couldn’t keep the launcher, but his interest and amazement showed that our design choice was the correct one. After all, the whole purpose of building a toy is to make sure that children enjoy it.
