Pumpkin Slinging

Matt here:
Shelley tells me that I am required to write on this blog entry so here goes.
This was a fun opportunity to get involved with some professional engineers and do something destructive. Our preliminary planning meeting was around the second week of Sept. Since then I have made five or six trips to I.F. and have put right around 20 hours into this thing.

The experience and the contacts that I have made have already and will continue to pay dividends into the future.


Here is the batch of pumpkins that we had to break. They ranged in weight from 3 to 5 pounds.


This is the second trebuchet that we built last weekend. The first one had some design flaws that we were able to fix in the second one. A problem that we had to address was that the 1 inch diameter stainless steel bar bent after the first couple of shots. This has been a "shoot from the hip" type of project so none of us sat down to figure out what kind of loads the bar would be subjected to when we shot it. To remedy this problem we made the frame narrower. This made it so the weight in the middle of the bar had less leverage which cured the problem.


Here is my beautiful wife Shelley and the stinker pot baby Lily. I am grateful to her for supporting me through this work. 3 or 4 of my saturdays and several nights I have had to spend away from them during this project.

Here is the shot gun affect. Four small pumpkins and an apple. They went about 200 feet.

A larger pumpkin shortly after release.

This is a great picture. See how the pumpkin is several feet above the sling. This shows that the pumkin released too early. One end of the sling is attached to the firing arm while the other has a loop tied in it which slides over a nail drove into the end of the firing arm. By adjusting the angle at which the nail is drove into the board, we can control the release angle of the sling. Ideally the sling would release when the firing arm is vertical and the sling is at a 45° angle to the firing arm. This is the ideal angle for distance with the firing arm in the fastest most powerful porion of it's arc.

Baby Lily is enjoying perhaps her last nice fall day in 2008

Good project. Hope I didn't bore you with the details.

Shelley here: This was really impressive!! Every launch was great. There weren't any bad runs. I loved watching. Matt didn't mention a few things. First of all, he built this. Matt did a lot of the designing and building. When we got there this morning, a man said to me, "Oh you must be Mrs. Matt-the-builder." They really liked him. Also, this was on the news tonight. I have it recorded if any of you want to come watch it. Matt is a star! He was excellent on the news. The students seemed to really enjoy this. Matt is such a great engineer. I'm so proud of him.