If you like blogs that post totally random articles with absolutely no regularity, then this is the blog for you. Or maybe not.

Monday, March 26, 2007

Cantaloupes + Physics + Too Much Free Time = Total Awesomeness

Yesterday, the SPS (Society of Physics Students) group here at KU hosted their first annual Canta-lobber contest - a competition in which contestants build a mechanical contraption that hurls a cantaloupe a ridiculous distance. The event totally rocked. There were "only" four entries this year, but with a lot of enthusiasm on everyone's part and with a good size crowd (about 100 people showed up), it was still lots of fun. If this first Canta-lobber is any indicator, year's Canta-lobber II - Electric Boogaloo will be totally awesome.

Here's a break down of the four contestants' machines and how well they performed.

4th Place - Team Antiseptic
Type: Trebuchet
Maximum distance: 153 feet

Ok, that's not their real name, but given the rickety (to say the least) nature of their trebuchet, I would consider it a success if no one on their team, or no one in the crowd for that matter, had to be rushed to the emergency room after this machine was in use. PVC tubing was used for most of the pivot arm, and said pivot arm was assembled and attached to the main structure using nylon twine and duct tape. That's not a typo: TWINE and DUCT TAPE. So, you can see why were were concerned about the possibility of someone being impaled.

Even though it was very worrisome to watch this device in motion, by the end they did manage to turn in a respectable performance.

Here's their first shot, so the "cringe factor" was still fairly minimal as the duct tape and twine hadn't started to fail yet, and the axel upon which the pivot arm was attached hadn't sagged almost to the point of failure. By the last shot, the counter-weight on the pivot arm was replaced with actual team members...that's right, their counter-weight was people! PEOPLE!

3rd Place - Team Partial Credit
Type: Trebuchet
Maximum Distance: 159 feet
Again, this wasn't the name of the team, but it kind of embodies the spirit of their design. It was a well made machine, and you could tell that a lot of thought went into the design. Well constructed using 2x4's and solid hardware, I had originally picked this group to finish in second place. But like a lot of things in life, the devil was in the details, and this group had a hard time getting to the "correct answer" of a good toss. So they had use up a couple of tries just to get the timing of the release of the cantaloupe right.

Their first shots either released too early and the cantaloupe climbed to a high apogee only to land very close to the trebuchet, or the cantaloupe was released too late in which case the cantaloupe's trip was very steep and very fast descent into the soft earth right in front of the trebuchet:

But, ultimately, persistance paid off and they finally got in some good shots by the end, good enough to keep them ahead of Team Antiseptic and in 3rd place:

2nd Place - Team Elastic
Type: Slingshot
Maximum Distance: 333 feet
Team Elastic's (again, not their real name) machine quickly became my favorite of the event. The only entry not to use the the trebuchet design and instead they created a gigantic slingshot using multiple bands of surgical tubing. The cantaloupe sat in a steel colander that was attached to the sets of tubing. A winching system was used to pull the colander back and a quick release mechanism was used to set the slingshot free.

Aside from its original design, it was incredibly reliable. Every shot easily cleared 200 feet, with no tweaking or maintance required. And after each shot, more sets of tubing were added and the launch angle was adjusted to maximize the range.
Here's their very first shot of the day, and an impressive one at that (around 200 feet):
Here's another shot, this one went farther than the first:

And until the last team went, here's the 333 foot shot that had Team Elastic in first place for most of the day:

1st Place - Team Goliath

Type: One Big-Ass Trebuchet

Maximum Distance: 406 feet

All the other entries took their shots first so as to get out of the way of Team Goliath's (again not their real name - catching on to the pattern here?) monstrosity. It sat quietly while the other entries competed in its shadow. It was a colossus that you knew would soon awaken from its slumber. And when that happened you didn't want to be anywhere near it. From the moment teams started assembling their contraptions, it became quite evident that Team Goliath was the team to beat.

The pivot arm of the trebuchet was made from a solid tree trunk. The counter-weights were five 140 pound tractor wheel weights and one John Deere storage container. This thing was designed to fling anything.

As massive and intimidating as this trebuchet was, it wasn't without its difficulties. As with other trebuchets, the release timing was also a factor with Team Goliath's machine. Although because their trebuchet had a larger potential (in every sense of the word), their misfires had a more comical outcome:

As they were able to get the release timing down, the trebuchet began showing what it was capable of (aside from actually flinging the cantaloupe in the forward direction):

Once Team Goliath solved the timing issues, they concluded their practice shots (which didn't count towards their standing - that's why they're called "practice" shots) with an impressive +300 foot shot that would have knocked Team Elastic from first place. Maybe it was overconfidence or maybe it was a desire to go for broke, but Team Goliath decided to try to leave all the competition behind and added several bags of sand to the John Deere storage container, bringing the total counter-weight of their trebuchet to approximately 950 pounds (that's almost half a ton)!

While this may have seemed like a good idea, this added weight resulted in changing the release timing, as was evident in their first official shot:

With an additional adjustment to the timing, the second shot resulted in a positive distance, but one that did not beat the current best official distance of 333 feet set by Team Elastic. Like any good epic story, this one would come down to the final shot for Team Goliath.

While the video isn't good enough to capture the cantaloupe as it's flung the distance, it's pretty clear from the crowd's response that Team Goliath's final shot beat Team Elastic's 333 foot shot. How far did it go? How does 406 feet grab you?

And to make this winning hurl even more dramatic, in the process of flinging the cantaloupe, the trebuchet's counter-weight snapped free from the pivot arm at the bottom of the swing, not only ending Team Goliath's competition for the day, but also requiring the base of the trebuchet to be completely repaired:

All in all, the competition was a great one. So, what did we learn? Well for starters, we learned that bigger doesn't necessarily mean better, as was shown by Team Elastic's dwarfed-in-comparison sling shot giving Team Goliath's massive trebuchet a run for the money. Second, we learned how to spell the word 'cantaloupe' - it's not cantelope. And lastly, we learned that even though it's only March, it's still a good idea to wear sunscreen.