Punkin’ chunkin’

We spent a couple of hours on Saturday morning at the Fourth Annual Howard Volunteer Fire Company Punkin’ Chunkin’. I discussed the same event and the three different sorts of catapults here in 2012 and again in 2013. The Trebuchet stores potential energy by raising a weight against the pull of gravity. When the weight is released, potential energy is transformed into kinetic energy which swings a massive arm, releasing the projectile. The Ballista works by storing potential energy in semi-rigid arms connected by ropes, much like a crossbow. My favorite catapult however is the Onaeger, or Torsion Catapult, shown in the first image. Imagine stretching a rubber band between two stationary pegs. Place a pencil between the lengths of rubber toward the middle of the span and wind the pencil around a few times. When you release the pencil the potential stored in the bands is released and the pencil will spin. The single torsion rope of the machine shown below was made of 1″ nylon and wrapped perhaps ten times between stationary posts. I was amazed that the projectile arm was twisted something less than 180° when the machine was ready for firing. I should mention that the members of Team Carbo, shown below, are the reigning World Champion Punkin’ Chunkers in the Torsion Division (their winning toss was measured at 3,105.34 feet). For the first time at this event, a compressed air canon was present. Team Sky Buster is currently ranked eleventh in the world in their division with a shot of 3,777.32 feet. My very particular reason for attending the Chunkin’ this year was to capture images which I wanted to try to stack, using a program called StarStaX, by Markus Enzweiler. This software is intended to be used to stack one hundred or more sequential images taken of the night sky to produce Star Trails. Although I haven’t yet tried my hand at this I thought the software might allow me to show the stages of a Punkin’ launch. The torsion catapult accelerated so quickly that its composite shot is composed of just four images.The second image of a trebuchet was constructed by stacking thirteen images. I liked the final product but wished that I could have selected just one of the thirteen to contribute the background information. As it is, the movements of four folks standing close to this catapult are distracting. The gentleman on the far right nodded his head during the sequence, the one to the far left took several steps forward. The gentleman who triggered the machine backed away from it after launch and I could not eliminate evidence of all of his movements from the final stack. I like the result anyway and especially enjoy the view of the punkin’ receding into the distance and over the lake. You may be interested to know that the burst rate of the D600 is 6 frames per second and that each shot was taken at 1/4000 of a second.

26 thoughts on “Punkin’ chunkin’

  1. Pingback: onager | Spanish-English Word Connections

  2. I am just catching up … and of course I like this “physics in everyday life” post, and I remember last year’s post 🙂
    It is also good to read a lighter “entertaining” post of yours – given the challenges you are currently facing!

    • Life is not nearly as oppressive as you make it out here Elke. If you are referring to the dispersal of our sheep … you should be viewing their departures as a good thing, really. We have simply decided it is time to part with the flock to, perhaps, allow us to pursue other interests. Having these animals go to good homes is important. So, that fact that we have begun moving the girls to other farms is good … we are glad for it. Thanks for your concerns. D

  3. There’s a tradition of naming weapons after animals. Examples include an airplane called the (A10) Warthog, the pistol called the Desert Eagle, a drone called the Predator, a glide bomb called the Viper Strike. I hadn’t heard of the Roman weapon called the onager, so I looked up the Latin word (which came from Greek) and found that it originally designated a wild donkey. I learned that we still use the name onager for what is zoologically Equus hemionus:


    I see that one of the places where it’s native is Syria.

    • Leave it to you to track this down. I had seen this particular catapult in action for the first time last year and hadn’t given the name of the weapon a second thought. You … or at least I … learn something every day! Thanks for your good sleuthing. D

  4. Once again I am reminded of how time flies. I do recall the previous such event. It was the first time I’d ever heard of such a thing. Of course it makes great sense from a physics perspective. I do look forward to the day when they add “magnetic rail gun” to the list of items that are allowed to impart the KE to the pumpkin … of course that will also involve cultivating a variety pumpkin with a higher-than-average ferrous content. Then again we could just cheat and put some iron shot in ’em 🙂

    • I should have known you would suggest a rail gun. I think I have replied elsewhere that the air cannon was high-power enough. As they were firing some test shots, before the real events of the day had gotten underway, I watched as a few pumpkins were turned to puree as they emerged from the tip of the barrel. I felt badly for the folks who were standing to the side and only slightly down range! Talk about needing a good shower when got home … puee! D

  5. Ah, I get it! That’s brilliant. When I first saw that last image of yours it looks like the guy in the blue baseball cap is just one of a set of weird septuplets. The ability to capture the trajectory of the pumpkin in a series of still shots and mash them together with software is amazing. All hail technology, I say!

    • Yes indeed. The introduction of all sorts of software to the world of digital photography is something I have very mixed feelings about. In this case, however, being able to generate an image which I wouldn’t be able to otherwise is one of the ‘up’ sides of these new capacities. I typically try and limit what I do to my images to the sorts of adjustments which could be made in an old-fashioned darkroom of the sort my Dad set up for me when I was a kid. There are all sorts of ‘crazy’ things folks do with images now and I don’t, usually, approve. D

    • Do you see that each image is actually a series of images sandwiched together? As the catapults were triggered I had my camera set to take a series of quick shots in very rapid succession. This way a series of shots capturing the throwing arm in various stages of its trajectory could be captured. The computer software was then able to sandwich together the images so that the result was a single image showing the throwing arms as they moved through their arc of motion … and in the second photo you can see the pumpkin sailing off into the far distance. D

  6. The program did a good job for you. Honestly, I hardly noticed the people or what they were doing. Too busy watching/looking at the captured swing of the catapult and the arc of the punkins. WOW … Spellcheck recognized punkins. That’s a pretty impressive toss … over 2/3 mile.

    • Yeah … it’s something that I wouldn’t have ever thought would interest me … but it does. Those machines have to be quite well thought out and well constructed to put up with the tensions and stresses created when they are actually set in motion. The torsion catapult is really rather scary to be near when it’s working … I’d love to run through a set of calculations which would tell me just how much pressure/tension/strain those ropes are under when the thing is primed to go. The accelerations are simply nuts. When the air cannon shot its first volley for the day the pumpkin was obliterated into a nearly liquid form as it left the end of the barrel … I can’t imagine how many g forces the thing experienced to have caused that to happen! It was a pretty fun morning. D

    • Yeah … but it really is fun to watch … and a nice day out for those who linger for the afternoon and partake of the food and other festivities. As it was, Joanna and I took off for home to catch up on all sorts of stuff which needed to be done. D

  7. Love your time lapse photography David … seeing the punkin’ (is that a pumpkin to those less knowledgeable?) on its path is most satisfying, like a physics diagram 🙂

    • Sorry for use of the slang Seonaid … I’m just using the local terminology … I think they used punkin’ for ‘pumpkin’ only because it fits better and is more lyrical when combined with chunkin’ which, I believe, is supposed to refer to the work chucking, for tossing or throwing. Perhaps I should have pointed this out! Sorry. I’m glad you liked the images … they were fun to construct. D

    • You know, after I realized that their movements weren’t going to render very well in the stack, I thought about saying something like, “Excuse me, could you either stand still or get please move out of my field of view.” And then, I thought about it and, in typical fashion, simply didn’t say a thing! Thanks for the positive reaction though … much appreciated. D

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