Maximize your punkin’ chunkin’ catapult with SolidWorks Simulation

Have you ever wondered how far you could throw a pumpkin? No? Me neither. However, a lot of people not only give this significant thought, they also meet in a big field to test their weird and wonderful contraptions at the Punkin’ Chunkin’ World Championships.

In a nutshell, teams compete to see how far they can launch a pumpkin by catapult, trebuchet, or air cannon. I first learned about this weird and wonderful completion a while ago, and I decided that rather than build my own physical catapult and test it, I would do the smart thing–build and test it in SolidWorks first.  Now, I didn’t want to spend a ton of time creating a detailed model to test; I just wanted a quick and dirty model that I could use to test my design hypothesis and make some initial determinations, namely:

1. What beam sections to use on the design?
2. Where to put the arm stop?
3. What are the impact stresses?
4. How far would the pumpkin go?

So my first design was quite basic, but it still had enough detail to provide meaningful design data. This is a really important point for any design analysis: analyze early and often to get the maximum benefit.

My first analysis was to see how far the pumpkin would be thrown using SolidWorks Motion.  The set-up was simple–apply a spring to drive the arm and a contact to stop it.

Unfortunately, my design underperformed significantly (but it was my first ever catapult design). But I knew I could use the optimization tools
inside SolidWorks Motion to alter my design.

The optimization showed that by moving the stop forward, the pumpkin distance was maximized. That’s good, but the downside is that the
launch velocity is decreased, as there is less time to accelerate the pumpkin.  We can also see from the geometry that the design needs a significant clean-up. But with the optimization result to work from, this is pretty easy to do.

So we now have new design that can throw the pumpkin a long way, but is it strong enough?  How flexible is it?  Have I used the correct
material and beam cross sections? Once more, I can turn to SolidWorks Simulation to answer these fundamental questions before detailing my design.

SolidWorks Simulation shows that the catapult arm has to withstand significant flexure and stresses, especially at the arm attachment point.

With this information ,my design went through one more round of design and testing before I was happy. It was light, strong, and it could fling
a pumpkin a long way. But I’m not going to show you all of the details, just in case we meet on the punkin’ chunkin’ jousting field. If you want to see more about how SolidWorks Simulation can help with your own punkin’ chunker (or most any other project), take a look at the video on our website.

So I now know what catapult I want to build; all I need now is a good excuse for my wife to allow me to build it. Any suggestions?

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