14 year old Joe Hudy has been having fun. From promoting science at Maker Faires to shooting marshmallows with the President at the White House, he’s the embodiment of STEM education effectively motivating a new generation about science and engineering, while showing how it can take them to some pretty cool places. Along the way, he’s tackled challenges and found passion and talent — his mother Julie describes the transformation with excitement and pride. “He’s gone from a shy boy with Asperger Syndrome to now a young man that wants to talk to everyone!”
Joe took time from his schedule to answer a few questions about how he got to the White House, and what he’s building next.
When did you start building? I only started really seriously to build things a year ago. I’ve made stuff in the past just for fun.
How did you get so motivated? I met a really cool man named Jeff from Elenco Electronics. I got in contact with them when my mom called to see if they had any Snap Circuits. Jeff Coda was the one who answered the phone. He helped me by giving me a soldering iron, oscilloscope, kits to learn to solder, bread boards, electrical components so I could learn more about electronics. He’s helped with with questions I’ve had too. He’s really cool.
What are some of the things you’ve made so far? I have made the air cannon, 3x3x3 Led Cube Arduino Shield, catapult, lazer light show, blinky lights. My favorite was the air cannon.
Obviously, it’s a huge honor to get invited to be part of the White House Science Fair. How did that came about? What were your feelings like leading up to and during the event? I was invited to go to the White House by Make and Cognizant. Make asked me and Cognizant sponsored me. I had met Make at Maker Faires. The whole experience was fun and exciting. I was nervous when I was talking to the president. I got to see a lot of sights while in DC.
About a year and a half ago I helped some producer friends shoot a “punkin chunkin” themed segment of a popular cable TV show. I had initially talked with them about building a catapult for the scene, but they were able to locate a guy who has his own oversized pumpkin-launching “potato gun,” so they asked if I’d just help out by appearing in the bit as one of the good ol’ boys having a laugh and firing off some shots of the cannon.
The launcher we used was a short length of large diameter steel pipe, capped off on one end. The triggering mechanism was a spark plug connected to an ignition coil, which unfortunately had the tendency to foul up quickly and had to be cleaned and replaced often. Word of warning: I strongly advise against using this method of pumpkin launching — it’s far too dangerous to play around with the explosive forces involved, and tends to be somewhat unreliable anyway. I was pretty nervous about the whole thing, actually.
The pumpkins were pretty tender and mostly ripped themselves to shreds upon firing, but the guys finally got the cannon dialed in and we blasted some good shots. In the segment, a pumpkin supposedly hits a guy who is stealing pumpkins far off in the field. Sorry to ruin the illusion, but this scenario didn’t really happen in real life — but we did have a lot of laughs that day. Watch the video at the top of this post and check it out. Also, notice my pal Chris in it as the DIY Technology Expert. I love that we got to appear in the same clip together.
Paper Trebuchet — a fun project for you projectile fans. Kill some time at work by printing the template, cutting it out, and folding it up. Then lay siege to your coworker’s sharpie collection.
This isn’t a traditional trebuchet in that it doesn’t use gravity to actuate the throwing arm, but it nonetheless mimics and demonstrates the motion involved. And it launches little projectiles pretty far! Great for a kid’s project, or homework assignment for you science or history teachers. I used it in a class I taught last summer and the kids loved building it.
Here are some notes on adjusting your trebuchet or catapult to help maximize the distance it will launch an object. Happy flingin’!
Catapults and trebuchets originated more than 2000 years ago, and over time became highly sophisticated machines that represented the pinnacle of medieval engineering. The largest machines were capable of consistently launching half-ton boulders hundreds of feet, knocking down thickly fortified stone castle walls – no small feat!
The general working property of a trebuchet isn’t too complex – it’s a large lever that works by multiplying the speed on a short arm by the ratio of its length compared to the long (throwing) arm. Gravity is used to provide the energy for this, in the form of a counterweight, and a sling is attached to the end of the throwing arm to further multiply the speed of the projectile. But within those few components, you have a multitude of variables, all which interact to affect the distance a machine can hit.
Here are some good tips for tuning your trebuchet for maximum effect:
One of the first pieces to consider is the ratio of the short arm to the throwing arm. General wisdom has a 5:1 ratio being the norm for a standard trebuchet, although 4:1 is sometimes used. The longer the ratio, the greater the speed that tip of the throwing arm will reach – but also increasing the force required to move it quickly.
A second component is the height that the axle will be placed above the platform of the trebuchet. Larger distances allow the throwing arm to be placed higher up, which increases the distance that it will travel when released. The further it travels, the more it will accelerate, which again increases tip speed on the throwing arm.
Obviously, there’s a connection between the counterweight and the throwing arm/projectile. General advice is that the optimal ratio is 133:1. A golf ball projectile (1.62 oz) should fire best with 13.46 lbs of counterweight – and a 14 lb bowling ball should have 1862 lbs pulling on the other side of the arm to reach maximum distance. Of course, this is all dependent on other variables and may differ for you, but is a good starting point for your machine.
The weight of the throwing arm should also be kept as low as possible, but not without damaging the integrity of it. A lightweight but strong material is advised for best results – for smaller machines ash can used, but on larger trebuchets, the strength of oak, aluminum, or even carbon fiber becomes necessary.
It is advisable to taper the throwing arm to keep it light at the tip. Meanwhile, the short arm should be stout and strong, as it has a lot of mass to support. Don’t be afraid to break it while testing – it’s good to know the limits and get as close to them as possible.
Sling length and pin angle work together to affect the angle of release. Longer length slings have a lower angle of release, good for line drives (if you need a direct hit against the castle gate, for instance). Shorter lengths will result in a higher angle of release, best for lobbing projectiles over tall objects. The general ratio to start at is a sling length (arm connection to tip of pouch) 80% the length of the throwing arm.
Modifying the release pin angle will also affect the trajectory of the launch. Forward facing by 30º is the norm – but the length of the sling and the angle of the pin interact greatly, so make sure to change both while testing to exploring the full potential.
Trebuchets large and small tend to have wheels, which initially appear to be for transport. And while this would be true for minor adjustments, the largest trebuchets were so massive and heavy that they would have to be assembled on location. The real purpose of the wheels is to allow the entire mechanism to move back and forth as the counterweight is released, keeping the weight’s movement as vertically linear as possible. A weight that rotates downwards loses some of the power of gravity as the force on it has to be transferred into a forward and then backward motion. But if the counterweight drops directly downwards, it can maximize the effect of gravity.
Not a major factor until very large builds are happening, do to the squaring effect of resistance due to wind. But for those who are working with large machines, making the moving parts (throwing arm, sling, pouch) as invisible as possible to the wind will help increase the distances.
Also, film and review your throws. A lot can be seen by checking the frames of your launches to determine what is happening, and where.
Many of these notes were taken from The Hurl, a great community of trebuchet and catapult enthusiasts. This thread on their forum details the tuning of a smaller trebuchet that was able to go from 30′ to 115′ throws with a variety of modifications. Quite an increase.
Ripcord’s trebuchet website has a tremendous amount of information on building and improving your catapult through better sling design and more. A must read.
Tonight (Dec 12) I will be hosting a live discussion on the Craftsman Experience live feed with Joseph Budka, who just completed a bowling ball launching trebuchet for this show. We spent a couple days playing with the machine and will discuss the trials and tribulations of assembling one of these awesome projects (including recovering from a catastrophic malfunction). Make sure to tune into the Craftsman facebook page and click the “Experience” tab to watch. 730pm EST, 430pm PST.
It’s autumn again. Such a wonderful time of year. Cider, hay rides, freshly bought school supplies. And launching things far through the air with catapults and trebuchets.
This year, instead of being a mere catapult observer, why not build your own? Building a basic trebuchet is really not that complex – it consists of a frame, a throwing arm, a counterweight, and a sling. The trickiest parts tend to be determining the sling release point, the bearings to get things rotating smoothly and deciding how big you want it to be. I’ve poured through various plans on the internet and have compiled a list of sites with notes to anyone that’s looking to make one for themselves.
Some of these are complete projects, while others are good for getting ideas on how to build your machine. Put it all together, add in some personal touches, and watch stuff go flying. Get busy!
MIT college project that became much bigger than originally intended. Built almost entirely from 2×4′s, combined together for added strength and support as needed. Counterweights are inefficiently attached directly to the throwing arm, rather than using a separate container that articulates downward from the arm. Was able to throw an object of undisclosed weight/size (water balloons) 204′ with their best published throw, a distance that should be able to be improved greatly with small changes, owing to the large size of the machine. No blueprints or specific materials (aside from 2×4′s, which was their only material), but a decent selection of build photos. Good site to help get ideas for large builds. Project cost: about $200. (link)
Do you want to launch a softball 50-60 feet without having to get down and dirty cutting wood, metal, and using power tools? Here’s an easy way to build a fairly sizeable trebuchet out of cardboard and a few other basic materials.
For this project, the components are glued together and assembled with bolts for the axles. A few small pieces of PVC are used to create axle bearings–this could be improved by using skateboard ball bearings instead (side note: it’s crazy that you can now get a single skate bearing for 99 cents). Also, a commenter makes a great point that adding wheels will allow the trebuchet to rock as the counterweight falls, which allows the counterweight to follow a much more efficient linear path and increases the capabilities of the machine.
Glued corrugated cardboard develops a decent amount of strength while remaining fairly lightweight. And as anyone that watched Punkin Chunkin knows, lower weight means faster speeds. Keeping the throwing arm as light as possible is key for massive launches.
Follow all the steps on the Instructable here: Cardboard Trebuchet. Also, I lied about the power tools part. You may need a drill to create the opening for your axle. No big deal.
And if you want something a little more desktop sized (plus kill some time at work), check out the Paper Trebuchet instructable too.
Part of hosting the Science Channel coverage of the 2009 Punkin Chunkin World Championships with Zach Selwyn means I get to do a few web videos to explain the ins-and-outs of how the amazing machines at the event work. These web spots are called “Behind the Chunk.” Here’s what I filmed, with some further information.
Air Cannons: Consist of three components: Chamber, valve and barrel.
With the valve closed, the chamber (a large tank) is pressurized with a compressor that is a lot bigger than the pancake compressor you get in a kit from Home Depot. On the other side of the valve, a pumpkin is placed at the bottom of the barrel, which can reach up to 100′ in length. A good pumpkin will have a spherical shape that sits perfectly inside the barrel to allow the least amount of air to flow past it. The valve is opened as quickly as possible (the winning machines’ valves are hydraulically actuated), and the pressurized air rushes out of the chamber and down the barrel. The speed and force of this air is sufficient to shove the pumpkin at an incredible rate of speed. On the furthest throws, the pumpkins approach supersonic speeds as they exit the barrel – very impressive.
Trebuchets: Consist of a counterweight, a throwing arm, and a sling
The simplest trebuchets work with the throwing arm mounted as a simple lever, with a huge weight on one end and the sling connected to the other. The weight is lifted overhead while the sling is loaded with ammunition. When the sling is dropped (usually through the use of a quick release mechanism), it lifts the opposite, longer end of the throwing arm upwards with considerable velocity. The sling that is connected to the throwing arm is whipped around with even greater speed, releasing the payload when moving beyond the threshold of an angled pin that keeps it in place.
A more advanced trebuchet design is called the floating arm trebuchet, where the counterweight is separate from the throwing arm, allowing it to drop in an entirely vertical axis to maximize the effects of gravity. Amazon sells a small floating arm trebuchet kit that can throw a golfball 200′. Merlin is a highly engineered floating arm trebuchet.
Centrifugals: Consist of a car or truck engine, gearbox, series of propshafts and axles, and armature
Instead of spinning wheels on the ground, the centrifugal machines use the same machination to spin a windmill-esque setup hoisted 30′ above the ground. A pumpkin is cradled carefully at one end of the armature, which is accelerated through the gears to maximum speed. Some teams add to that top speed by then pumping other accelerants into the engine just before hitting the trigger, which releases the pumpkin at a preset point in the spin. This point of release is ingeniously controlled by a repurposed auto distributor setup. At the speed when the pumpkin is released, it’s hard to not be afraid for your safety and everyone else’s in the immediate vicinity. They spin like a helicopter on its side. Inertia II is a new centrifugal machine at Punkin Chunkin in 2009.
The twisted rope bundle is maybe the perfect form of energy to power a catapult. As the rope is twisted, it stores a rotational energy in what becomes a torsion spring. This rotational energy transfers directly to the throwing arm that is tucked inside it. The arm is cocked into the loaded position, the sling is put in place, and the ammo is loaded inside. A quick release is triggered, the rope bundle snaps the arm forward and the sling whips overhead, launching its cargo with incredible speed.
Super cool program: Trebstar, a Mac and PC trebuchet modeling software, calculates the range and efficiency of your trebuchet design.
The program has various configurable parameters and animations, and also shows the forces on the different components of the trebuchet itself – lets you know what part might break when you build your masterpiece. A handy tool for aspiring punkin chunkers! And a quick reminder: watch me on Science channel’s Punkin Chunkin special this Thanksgiving. It’s awesome.
I’m hosting the 2009 Punkin Chunkin competition alongside my Catch It Keep It pal Zach Selwyn. During the preliminary filming, we stopped to visit with “Sir Chunks A Lot” — a team hailing from southern New Jersey. I spent the day learning about their approach to the competition, growing pumpkins, and testing their rubberband-powered catapult. The rubberbands on these machines aren’t the ones you wrap your newspaper with — they’re about as thick as a 2″ piece of PVC pipe. For those test shots, the team uses bowling balls, which gives them a consistent shape and weight for each shot. I’ve never seen anything like watching a bowling ball whip through the air with so much backspin that it creates lift like a perfectly hit golfball at the driving range — on some shots, the finger holes on the ball made a whistling sound, like a whiffle ball — but it lasted for a good quarter minute or longer. Watch the speed on this thing – and it’s only at 70% power.
Every year in Delaware, a group of backyard engineers gathers with a single goal of seeing who can launch a pumpkin the furthest. The event is called Punkin Chunkin, and in the early years, the machines slowly pushed into the hundreds of feet. In short time the flying pumpkins passed the 1000′ mark, then the 2000′ mark, and are now closing in on the “holy grail” of chunkin’: one mile.
Calling these catapults “homemade” is something of a tease – sure, the machines that the participants mastermind for this event are all entirely custom built. Some of them even laugh that every year someone asks “Wow, where did you buy that?” – a testament to the years of work that goes into crafting each and every part of the machines, giving them such amazing throwing power. The event itself has become a gathering of the world’s foremost experts in the realm of catapult and trebuchet technology, and the innovations happening are pushing past anything that’s been imagined.
Hi, I'm Mike. I’m the co-host of Science channel’s Punkin' Chunkin' and Catch It Keep It. I work on TV shows explaining and building crazy machines that crush stuff, blow things up, shoot fire, all in the name of science.
I'm a contributor to Wired and a former staffer at ReadyMade, two awesome magazines that focus on technology and diy living.
This site is where I keep a list of instructions for fun projects I've done, am working on, or draw inspiration from. I encourage everyone to get involved -- get up and make something!
New product in my store -- mini skull silicone molds!