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This is the world premier for our new trebuchet design. Not only is this trebuchet simple, it is extremely efficient. It has many of the advantages of a floating arm trebuchet, but with fewer parts, less friction, and a unique projectile launch path. As you can see in my son's video, above, the projectile never swings backward beyond its starting point, reducing the danger to bystanders behind the trebuchet. Using this design last fall, my 8 year old son set the all-time record for best design at the Vermont Pumpkin Chuckin' Festival. His 20 pound, 41 inch tall trebuchet threw a 3 ounce ball 266 feet. My 500 pound, 10 foot version threw a 5 pound cantaloupe over 700 feet, but it went so high and so far that the spotter never saw it pass over him on its way into the woods. You can read about these trebuchets' success here on the VT Pumpkin Chuckin site, and you can see mine in action in the video above.

The instructions provided here show how to make a 20 pound, 41 inch version, like my son's. The dimensions were chosen to adhere to the lightweight division rules at the VT Pumpkin Chuckin' Festival. As you will see, my son did all of the work himself. I did help out by holding some things in place and showing him how to complete the steps.

I have made other versions of this trebuchet with longer arms, mostly for throwing the excess apples that fall in our yard. While they would not be legal at our state competition, they can really whip an apple.

[**Update: In response to one of the replies, I just made a small, 3-D printed version and added a video. I was going for a desktop version, but it seems more at home on carpet. This is a rough version 1.0, but I attached a .stl file if anyone wants to print one and doesn't have CAD capabilities (scroll down, below the supply and tool lists). I used pieces of a large paper clip for the spikes and the finger. For good measure, I sharpened the spikes with sandpaper. I used fishing line for the sling and the tuning string. As you can see in the video, there's no pouch on this version. The sling is just one loop of fishing line, and it is permanently attached to the projectile. They fly off together. The proportions are different than those of the larger versions, which may be why I needed to bend the finger forward on this one to get a good release angle.]

Step 1: Parts of the Walking Arm Trebuchet

Picture of Parts of the Walking Arm Trebuchet
cover 2.jpg

These diagrams show the names I will be using for the trebuchet parts in the following steps. The triangle spikes, which serve to keep the triangle from slipping when it hits the ground, are most visible in the front and side views.

so smart
J Crafts12 days ago
This is an awesome design!
ya yeet?
g19fanatic6 days ago
I love this design. its very simple yet effective!

Could you upload a video of how you would 'arm' the big 500lb one? I'd be interested in seeing that process..

Also, if you were trying to hit a target, what would be the best way with this design to 'aim'? Remove/add weight? Adjust the tuning string? Have you tried for accuracy versus distance with this design?

btw, you were linked on hackaday :)
mrstapleton (author)  g19fanatic5 days ago
Thanks for the link!
Regarding loading the big one, I take the weights off, stand up the trebuchet, and then put the weights back on, one-by-one. It sounds pretty labor intensive, and I guess it is, but compared to most of the other big trebuchets I've seen, it goes pretty smoothly. I've only had one scary moment. The first time I launched it, the stakes for my guy lines weren't long enough, and the trebuchet started to fall over as I was adding the 8th or 9th 45 pound weight. As I recall, I dropped the weights and jumped off my ladder, and the trebuchet fell semi-gracefully to one side.

Right now it's up in my barn loft, but I will be getting it out again for pumpkin chucking one week from next Sunday. I'll get some video of the loading process then. I've thought about rigging up a winch to lift it up with the weights still on it, but it hasn't been worth the trouble.

I haven't put much effort into trying to hit targets with it. I'm a science teacher, so I'm a little ashamed that I really haven't done much controlled scientific testing. I'm just not that self disciplined when I'm out shooting trebuchets. So while I may have some good ideas here, I may end up being only about 51% correct. That said, to get a lower trajectory I would first adjust the tuning string. In general the trebuchet shoots lower when the triangle is lower. You could also add an adjustable finger to delay or speed up the release. I think a shorter sling should also cause the projectile to swing around faster and therefore throw lower. Up to a point, I think adding weights should both increase projectile speed and lower the launch angle. I will say that when we tried throwing water balloons with it, we actually had a hard time hitting the house (and not throwing over it). That doesn't bode well for this being a precision instrument of destruction, but those water balloons are squishy and wiggly, and maybe that was our problem. Plus, the house was uphill.

If I wanted to attack something tomorrow, I think I would start by making about a 6 foot trebuchet with 50+ pounds of counterweight, and I would throw projectiles the size of an apple. That would be pretty easy for me to manage manually and to aim at a variety of targets.
espdp27 days ago
Yay! Gotta make one with the kids now!
Congratulations on getting the Grand prize on Make It Fly! I am making this as a tech project now :)
mrstapleton (author)  Paper Mechanic11 days ago
Thanks! I hope it works well for you.
You suck just like mac!
Elegant design! Now we just need to see if it scales down and can be 3d printed.
mrstapleton (author)  TooManyScooters12 days ago
My first 3-D printed version worked pretty well. I just added a video to the first step, but here's the link. I was excited to try it out, so instead of bothering with a tiny sling pouch, I attached a permanent loop of fishing line to the hot glue projectile (painted black). The fishing line loop goes around the finger, and the whole thing (loop plus projectile) gets thrown together. As I expected, getting traction for the triangle wasn't easy. The triangle spikes are paper clips that I sharpened. If I had sharpened them some more, I might not have needed the paper towel.
That is pure magic! I must try this as soon as is possible. Maybe an entire base plate could be printed to have a set groove/wall for the triangle bass to lodge against and an alignment point for the pivot rest (thin tapered end). Maybe two pieces joined by dowel or similar. I can't wait!
mrstapleton (author)  TooManyScooters12 days ago
It works better on the carpet. In the video with the mouse pad and paper towel, you can see that the whole mouse pad shifts forward. Here it is on the carpet...
mrstapleton (author)  TooManyScooters13 days ago
Thank you! I would expect scaling down to work fine. I've been thinking of making a desktop version. Aside from the issue of the miniature sling and pouch, the trickiest part (I think) is going to be getting the triangle to dig in and not slide forward. The most simplest solution I can think of is to launch it on a mouse pad, and have little paper clip spikes that dig into the mouse pad. I just sent a quick model to the 3-D printer. I'll let you know if it works.
Biodynamic13 days ago
My first thought... I need one of these. Thank you for sharing!
mrstapleton (author)  Biodynamic12 days ago
You're welcome!
HoldOnTight13 days ago
This is a great project to get children involved in making something easy and fun! I hope he and others try to improve it.
mrstapleton (author)  HoldOnTight12 days ago
My son definitely enjoyed it. Thank you!
This is very interesting.
mrstapleton (author)  Cats Science Club12 days ago
ChrisWx13 days ago
I'm betting it took exactly One launch for your Retriever to figure out what was going to happen the next time! I laughed at how excited he got when you called him over to launch it.
mrstapleton (author)  ChrisWx12 days ago
Yes. And now she goes nuts any time she sees a trebuchet. Even more exciting than squirrels and chipmunks.
rpmccarty1712 days ago
I do not see any notes about the # or size of the weights used for this project. Can you please share if there are 2 or 3 weights used and the poundage of each weight. Thanks
mrstapleton (author)  rpmccarty1712 days ago
Good catch! I just edited the step with the weights to reflect their magnitudes (2.5 lb, 5 lb, and 10 lb). They were listed on the supplies page but not in the instructions.
ChrisWx13 days ago
Regarding the water comment - energy cannot be removed from the system. Water would slow the spin induced by the sling, which would affect wind resistance and accuracy, but wouldn't affect the tuning of the trebuchet at all - since tuning is what you used it for, not the competition, it's perfect. With such a short time of flight, the effect on distance would be barely measurable in any case.

I would Love to experiment with this design. Some kind of mechanism to fine-tune the finger angle for release time would be awesome. From the slo-mo vids, your release angle was, as close as I can tell, a perfect 45 degrees - great for distance. I have to wonder what it could do regarding projectile speed with a later release. Wouldn't get the distance, of course, but it would pack a mean punch closer in! :-)
procter13 days ago
Excellent work and innovative.
It certainly makes me want to throw up :-)
Well done, thanks.
BakerBoy713 days ago
This is awesome. I always wanted to build a traditional trebuchet, but this looks simpler and withing my ability to make!
RichFarwell13 days ago
Really neat! Now I know what to do with all our frozen tomatoes -- besides making tomato sauce.... ;-)
FlorinJ14 days ago
Don't fill the racquetball with water. The water will flow in all kinds of crazy patterns and consume from the ball's energy. Fill it with something solid, and make sure that either the ball is full or the solid is evenly spread inside the ball, so the center of mass and the center of pressure are approximately in the same spot. This should add several yards to how far the ball travels.

Heated grease would be an option, I think. Lighter than water, so you can fill more of the empty volume, and if you fill it while it's hot, you can still use a syringe, but if you roll the ball on a cold surface for a while after filling, it should solidify as a layer of approximately uniform thickness inside the ball.
mrstapleton (author)  FlorinJ14 days ago
Great idea! Thanks!
drjefferson14 days ago
Exceptional engineering conceptualization/fabrication/ &
explanation. It is heartening to see
again that there are quiet Da Vinci’s always walking among us.
mrstapleton (author)  drjefferson14 days ago
Thank you! A lot of the credit goes to Dave Jordan, the guy who started the VT Pumpkin Chuckin’ Festival. Each competitive division has a total weight limit for the trebuchet plus it’s counterweight, so there is a strong incentive to build light and seek simplicity. It’s a fun problem.
jmacuk14 days ago
Awesome new design! I can't wait to share it with my students!
mrstapleton (author)  jmacuk14 days ago
Great! I’m a teacher, too. My engineering class is in the midst of their own trebuchet design project.
CraftAndu16 days ago
This is so cool!
jimwi17 days ago
This is so awesome i have to make one or more.
Can you through water balloons/booms with it or do the G forces burst them?
mrstapleton (author)  jimwi17 days ago
That's a good question about water balloons. I suppose it depends on how tough the balloons are. I'll ask my son if he has some that we can try.
When you test the water balloons please add video. I was thinking you could launch a hand full at at a time for a hale storm booming LOL.
I just had a look at the pumpkin chucking comp and see you guys blue away the rest of the field. Made me LOL reading the results.
Well done.

mrstapleton (author)  jimwi16 days ago
We tried some water balloons today. The g's did destroy them. They sprayed all over before the pouch released. Then we tried some 12" balloons, but we kept them the size of regular water balloons. They survived the launch, and they broke when we hit the side of the house with them. Our yard slopes up toward the house, and we had a surprisingly hard time not throwing over it. Most of the balloons that went over the house survived the impact in the yard on the other side. I uploaded a video, but I'm not sure if it will work, since I used the "add images" button. If it doesn't work, I can use a YouTube link. The hail storm of balloons concept would take some work. I think you could do it with a large trebuchet and a bunch of tough balloons of the non-water balloon variety.
Thanks. You guys are awesome.
You have inspired me got me thinking. I have watched your vids over and over again.
Thanks again . keep up the good work. and yes I voted hope you win.

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