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ASME Watermelon Launch





Today was the day for the Melon Felon's public debut. The Second Annual Watermelon Launch at RIT, sponsored by the RIT ASME chapter was the place. Due to the short time line in which to make a machine and get ready to compete, we got very little testing done.

What testing we did do leading up to the event was all done with a soccer ball, which weighs in around 14 ounces, no where near the 3-5 pounds that we were due to be shooting with. These tests were also only done with up to 200 pounds of counterweight, a far cry from the 300 we designed for. The counterweight issue was mainly due to the fact that we were trying to avoid buying 12 new 25 pound barbell plates at a cost of roughly $180. Chris was able to borrow 6 Olympic plates, which was good, but they were unfortunately thicker than the standard plates we designed the width for. We thought we might be able to fit 6 standards and 6 Olympics on, but we weren't sure. Due to a lack of weights being available at local thrift stores, we were forced to buy 6 new standard plates, and this was done only a few days before the competition.

So, we were going into the competition with no idea of how the machine would behave. When we got there, we were also upset to find out that the University of Rochester team had indeed brought an air cannon, like we had heard rumors of possibly happening. Mechanical devices simply cannot compete with air cannons if both are roughly the same size. As there was a size restriction, we were sunk. We felt that we had a chance to win or at least do well in the accuracy portion of the competition, which consisted of taking the best of 2 shots at a target 100 feet away. The team that had the closest shot would get the full 100 points, the team furthest would get the minimum 20 points, and all others scaled in between. The same idea was true for the distance, which was where we felt the greatest trouble would be with an untested machine.

100 feet should have been well within our range, and had we had time to test with full counterweight and a representative weight, we might have been fine. But, we hadn't. Our one test shot went straight up and landed less than 2 feet behind the Melon Felon. Then the competition began, we were to launch third out of four teams, with the air cannon of U of R closing it out. Looking at the other machines, we felt that we had a chance to at least take second, as neither of the other two machines threw all that far.

The ASME catapult was first to fire. This machine was basically an arm powered by a pair of garage door springs. They did very well with the accuracy, as their machine was zeroed in for 100 feet perfectly. In fact, they won the accuracy portion, placing a shot just over 8 feet from the target's center. But their machine did not have the power to clear 100 feet, and their best distance shot went only 97.58 feet.

Then Team Junkyard Wars went. Their machine is hard to describe. It was a conglomeration of various car parts and a kitchen pot to hold the watermelon. It did not shoot very far at all. Their best accuracy shot landed 66 feet away from the target. While cranking down their arm for their first distance shot, the steel cable that held everything together broke, and their day was done.

Now it was our turn. We took a guess as to how much counterweight we would need to go 100 feet, we tried 200 pounds. Our release on both accuracy shots was way before the arm stalled, robbing us of most of the power, and the flight trajectory was very high, all leading to a closest shot that landed 22.5 feet from the target's center. Not terrible, considering, that got us 80.04 points out of a possible 100. But when we went to load up the full 300 pounds of counterweight, we found that the Olympic weights were just a touch too wide to allow another 6 standard plates on in between our hangers, and so we had to live with 275 pounds of counterweight. Still, we felt that we could beat the 97 foot mark of ASME and possibly take second place. But our releases were still at high trajectories and well before stall, and we only managed to get a shot out to 86.6 feet. We were struggling with our release all day, and had a couple of misfires as the sling gave us some trouble. It just wasn't our day, but we had at least locked up 3rd place, as the Junkyard Wars catapult only had 20 points.

Now for the clear favorites, the U of R ASME team with their air cannon. We all knew it should be able to shoot far if it didn't explode their melons, but how would it do at accuracy? Pretty well turned out to be the answer, as they put a melon 10.8 feet from the target, good for 96.19 points. Now we were really hoping for them to break their melons on both of their distance shots, as that would get us second place. Well, that didn't exactly happen. Their first distance shot went a ridiculous 650 feet. It disappeared into the trees at the end of the range. And with that, we were in third. They did pie their 2nd distance shot, but it really didn't matter.

In hindsight, we needed to do more (try any) testing. Then we would have at least had a chance of reaching the target. But there had been no time to do more testing, though we could have tested with a more representative weight. One other issue that we were fighting was that the lightest watermelons that we could find were around 5.5-6 pounds, so we were firing with a roughly 45:1 weight ratio, instead of the 100:1 we designed for. This issue needs to be addressed for next year. We do feel that we should not have been saddled with the minimum 20 points for distance because the Junkyard Wars Launcher broke, but this really would not have affected the results much in the end. O well.

Here is a summary of the final results:

Team Accuracy Distance Total
University of Rochester ASME (air cannon) 10.8 feet = 96.19 points ~650 feet = 100 points 196.19 points
Rochester Institute of Technology ASME (spring catapult) 8.04 feet = 100 points 97.58 feet = 21.56 points 121.56 points
Us (Melon Felon) 22.5 feet = 80.04 points 86.6 feet = 20 points 100.04 points
Junkyard Wars (weird looking catapult) 66 feet = 20 points broke 20 points





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Use "common sense" when operating trebuchets and catapults. Even little ones can be dangerous. Do not place anything you are not willing to lose in the plane of the arm rotation (this includes yourself, body parts, car windshields, cameras, etc). These catapults and trebuchets are capable of throwing just as far backwards as forwards, and the use of a backstop of some sort is recommended, though the use of one does not make the region behind it safe.

Also, just because the throw got away safely downrange does not mean the end of the danger. The arm is likely still swinging wildly along with the counterweight, and there is a sling whipping around. One thing many people fail to take into account is this sling; some people put a metal ring on the slip end of the sling and this ring can HURT when whipping around!

Have fun hurling, but please KEEP IT SAFE!!!