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Picture of Floating Arm Trebuchet (F2K)
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Ladies and gentlemen, I present to you:
The FIRST EVER (Free) COMPLETE GUIDE FOR CREATING YOUR VERY OWN FLOATING ARM TREBUCHET

Of this size, anyway. When i was looking for a good set of plans for a floating arm trebuchet, i couldn't find a single free one. I know that a lot of people share my frustration in not being able to find free plans- so I wanted to create the first one. This is a guide that will show you exactly how to build one.  As always, let me know if there is anything I can do to improve it-and I will add a video after I figure out how to.


I had a school science project (not fun) so I wanted to make it fun by building something cool. My friend and I previously made a catapult that was 7 feet high, and threw a baseball 40 ft. It was pretty bad. So this is a way to make up for that. The height of the channels is 8 feet, But the arm rises higher than that in its resting position. The arm is 7 feet. The short arm/ long arm ratio is what I was testing, and the different ratios are 2:1, 2.5:1, 3:1 and 3.5:1.  I won't tell you which one was the best yet, although you can probably guess. The counterweight is about 36 pounds, but the big, wide wood piece (the short arm) was probably around 20 lbs. I'm still not quite sure...  The total cost for me was around 130$.  I don't think it was more than that.

If you want more information on how a floating arm trebuchet works, there are plenty of videos on the internet.
I would visit Ron Toms's site, he's the inventor of this type of trebuchet.



I want to apologize for not having very many pictures of the building process, but I made sketchup models, so hopefully they will help. There are several things that could be improved, which are listed on the last page. The first good throw was about 206 feet, although the trajectory was way too steep, to the point where we could not see the baseball. So, I'm guessing that a baseball would go in excess of 300 feet! And that's with only about 50 pounds of counterweight. A 1 lb projectile would probably go about the same distance. Trust me, it's powerful. We just need to fix the pin and find the best sling length. The sling length is also probably not perfect. I'm still tweaking. Most throws went either straight down or backwards. The backwards throws were caused by a glitch in the guide system for the arm as it falls. The pin was also previously a double-headed nail and a keychain ring. The ridges in that ring would sometimes get caught on the two heads of the nail, which we think is the reason for the downward throws. So, you should include in this project the turnbuckle pin system, which is based off of this trebuchet: http://www.trebuchet.com/10101 
.
The entire thing took me about 2 months to build, but I wasn't working on it every day.
The diagonal 2 X 6s that attach to the longer drop shannel diagonals were not included in this instructable because they were a lot of trouble to add to it and I don't think they were really needed or worth it.

Always be careful; never fire it around windows or people.
Also, be very careful with the trigger. When you pull it out, it tends to fly towards the person pulling the trigger very quickly. Always hold the rope at the very end and jump out of the way after you pull it.
Let's start...
Oh but wait before you do...Remember to look at EVERY SINGLE ONE of the picture notes. I'm sure they'll help you a lot...


Credits: (Yes I just had to)
My mom and dad for paying for (almost) all of it
and for putting up with a messy cluttered garage
My friend, Michael, for always helping me with the loading and firing.
My neighbor and.. older friend, Joe, (He's an adult) for giving me tips on building the thing, especially the trigger design. He always believed it would work, unlike my dad. But my dad payed for most of it so I can't complain.
Coby helped move the trebuchet back from school (His grandpa has a pickup truck) and also helped me load and fire on one of the testing days.

Thank you to everyone that helped.

 
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stormfire1019 months ago

how long was the arm after the extension?

scull_mech11 months ago
Awesome trebuchet! I like the adjustable arm ratio. I just posted an instructible of our own design, it's a lot beefier, we threw 10-15 lb pumpkins around 300ft, and we actually got 720 lbs in counterweight on it, not including the weight bar or short arm. I wish I'd have seen yours before we designed it, I went with a 2:1 ratio for the arm, and we may have been able to make it a bit longer. Take a look at our trigger design if you ever want something that works for heavy payloads.
suprspi1 year ago
This is stellar. I really appreciate your work in building this instructable.

We just built an hinged counterweight trebuchet for our annual group camp of friends from highschool (we're all in our 30s now....).

We're all a bit nerdy and geeky and figured a weekend engineering challenge was a good way to make camping and drinking more awesome. We built a trebuchet that we call the medieval stuff chucker (MSC). I have included a link to a hack-up vid I made on youtube in case you're interested.

I really want to build a floating arm trebuchet, so maybe I'll do that between this year and next and we'll have stuff chucking competitions. Here's some vid of ours. http://youtu.be/MS9OepeTELc
frankenboom (author)  suprspi1 year ago
Thanks for your appreciation :D
I would love to check out the Medieval Stuff Chucker, but the link to the youtube video doesn't work.
If you do end up building a floating arm trebuchet, please let me know. I would love to see it while being constructed and finished.

ausmelone1 year ago
I'm nearly done with the trebuchet but I'm having trouble understanding the sling. I don't know how long to make the rope or how to attach the sling or how it is even supposed to work? I've made the pouch and strung one side through but from then on I'm lost. Please help because this project is due the 20th.
frankenboom (author)  ausmelone1 year ago
The length of the end of the arm to the center of the sling should be 1/2- 2/3 the length of the entire arm. A shorter length sling will work better for lighter projectiles, while a longer length will be better for heavier projectiles. You're going to have to do some testing and fiddling to find out what works best.
Now, to attach it:
Imagine the pouch itself. It has two ropes coming off it, one in either direction.

-----------(pouch)-----------

One end is tied through a hole that's drilled in the end of the arm. You do not want this side to come undone, so make sure it's tied tightly to the end of the arm however you can.
The second length of rope is tied to a small ring- like a loose keychain ring.
On the end of the arm, there will also be a nail, or some sort of strong metal pin. This metal loop goes around the pin, and as the centrifugal force increases as the arm swings, the ring slides off the pin to allow the pouch to open.
so its looks like this... if you can use some imagination :P
and if it doesnt get messed up once i post this

(======arm=======--)(----------rope------------)(sling)(----------rope------------)0
^that's the pin tied to sling ring tied to end of rope^

I realize that wasn't an awesome explanation, let me know if you still don't get it.
And send me some pictures :D
ausmelone1 year ago
I tried to reply but it wouldnt let me so this is my other option. So, This project is not due until sometime in may, but I will be glad to post pictures. Two last things...

How much will this cost?

And, I'm not looking to chuck this 200yds. I will be launching this in a range 200yds and I'm looking to toss under that because I will be demonstrating my trebuchet about 50yds or so from a football field and I will be tossing the weight towards the field and at the other end is a parking lot. So if I could toss the weight a 100yds would be perfect.
frankenboom (author)  ausmelone1 year ago
It cost me about $130 not including the weights.
If you need to beef things up, like the counterweight bolt and wheels, it might cost more. But make sure you go to the website for wheels that I recommended in the Instructable to avoid paying too much for wheels.
And as for tossing a weight that far, you would need to change the ratios on the arm yourself and work with different sling lengths. If you could find a simulator that would be great, but I never could. It takes awhile to calibrate the different lengths and ratios to reach optimal firing capabilities.
ausmelone1 year ago
I may or may not fget a response considering it is 2013 and not 2010 but I need to build a trebuchet for my physics class and i came across your model and had a few questions. I will be modeling my trebuchet after your and would like to know...
Can the trebuchet launch a 2-lb dumbell?
Can the trebuchet launch a 6-lb shot?
If I need to bring the scale down, what would the dimensions be?
frankenboom (author)  ausmelone1 year ago
The trebuchet, as is, would probably not be able to launch such a heavy projectile, but I'm not sure. To launch such a heavy projectile will require much more weight than the approx. 50 pounds that was used here.
The main problems would be the extra weight needed to really make the 6 pound weight fly, which would put extra strain on the wheels on the arm and the bolt holding them, the counterweight bolt, the counterweight boxes, the sling, the sling lines and the trigger assembly. Oh, and the arm itself. I haven't noticed any cracking with a 1 pound weight being fired at full speed, but a 6 lb weight will exert much more force on the arm because of its higher inertia..
Essentially, beef up the arm assembly. And do lots of testing, with a realllllly long trigger string.

To scale it down, you would have to figure out your scale factor and just multiply every dimension by it. Alternatively, you could download the sketchup model, highlight the entire thing, scale it down and get the dimensions directly from there.
frankenboom (author)  frankenboom1 year ago
If you need any more help feel free to let me know, and it would be great to see a picture of the final thing.
QuiK_StiX2 years ago
do you have the exact dimensions of the final product. it would be much appreciated!! i am building a trebuchet for my physics class. i need to make mine 3x3x3. so i need to cut length of everything down to size. will this still work that small? thank you
frankenboom (author)  QuiK_StiX2 years ago
Sorry I haven't responded until now. I don't remember the exact dimensions, but I think it was a little bit taller than 8 feet, and about 6 feet long. Width was around 2 feet, I think. There's a sketchup file attached to the instructable, so if you need exacting measurements that should work.
Although the trebuchet will work so small, it might be better to increase the arm ration. Give it more of a flicking action than a long drawn out flinging.
I don't really know what I'm talking about.
Do some experiments, that part is the most fun.
thank you very much. i will keep that in mind. if theres is any other advice that you can give me (especially for it being smaller) it would be a lot of help.
samgmills3 years ago
Pretty nice, but you could get a lot more power by lowering your tracks by about a foot. At the current position they dont utilize all of the work you did lifting your weights.

Here is a floating arm that two other students and I from FRC team 11 MORT designed for punkin chunkin in Delaware. As far as we know, its the largest floating arm ever built by youths, and the largest wooden floating arm trebuchet in existance.

The arm is 18 feet long, we use a 1.5 inch steel bar, and can load it up to about 800 pounds.

http://mort11.org/pumpkin

also be sure to check out the rest of our website, FIRST is a great program for anyone interested in engineering!

frankenboom (author)  samgmills3 years ago
yes you're definitely right.
I only figured it out after i screwed everything together..
I actually didn't draw up ANYTHING for this before I started (BAD idea)
and realized that the short arm was...too short.
I'm a very lazy person, so I just let it be.
Eventually , I WILL fix it; it's just that I have no time over the weekdays and have limited time over the weekends (I wake up really late- like a sloth).
...Anyway...
I'll either make the short arm longer or just lower the tracks like you suggested...
still pondering. If you have ANY better ideas, let me know.
I revere you.
The program you're in looks AMAZING!
and, of course, the trebuchet does, too...
In fact, it was trebuchet like this yours that inspired me to make a trebuchet for my science project.
AND I had seen the MORT treb before this (on youtube). You guys really get around, huh?
Now, i have a few questions for you, mr gills, sir man.
WAS the steel bar hardened?
DID it bend at all?
and last ut not least...
HOW long did it take you to make?

...that's it.
GOOD LUCK in the punkin chunkin contest...I'll be watching it on Discovery.
-nico

Wow considering you did that without any planning is really impressive we used 3d drawing software to work on ours for about a month or two before we started.

Sadly no, our steel bar was not hardened. We did special order it and it was very high grade steel so it did not bend for a while, but yes it bent after our 800 pound throw. To send it out to get heat hardened would have taken about two weeks that we needed for practice throws.

If you include planning, we started in August, and started actually build in September. And we were done by November 3 for Delaware, which already passed. The TV people need about a month to edit and such.

We had a few problems such as throwing at the wrong angle and having friction on our bar that kept us from winning. We came in third to a smaller floating arm trebuchet.

And last but certainly not least, yes, FIRST is a great program and I can say with confidence that it is the best thing i have done with my life thus far. Im sure there is something in the terms and conditions about not asking where you live so i cant say which teams are near you but yo should be able to check here and maybe start a team of your own. Its hard work but you wont regret it.

http://www.usfirst.org/roboticsprograms/frc
frankenboom (author)  samgmills3 years ago
Wow that's great! the bar didn't bend until your 800 pound shot.
That means a 1 inch bar should be fine for me...
My trebuchet almost always fired at the wrong angle because the pin I used was a double-headed nail. The ridges were large, and caught on the ring.
Usually, it would throw the ball straight down.
I also had the same problem with friction. A lot of the time it would actually stop halfway down. If one side was rubbing more than the other, the bar would tilt and pull the channels together. Luckily, nothing ever broke.
Third is impressive. For a NATIONAL competition. And I'm sure you'll be better next year.
Also, I live in Coral Gables (near miami).
Yup, that's a ways away from you.
I'm in SECME, which is just..ehhh...
It's O.K...not great. It's more doing than learning and doing. (No knowledgable counselors, etc.)
I'll look into starting or joining a team.
-nico
I want to build a trebuchet for a physics project with 3 other students. Could I use this design to launch a 5 lb. pumpkin about 200 yards?
frankenboom (author)  JediKnightTemplar3 years ago
First, sorry for the slow response. I've been occupied-it's my freshman year in high school and I'm still not used to it.
ANYWAY
I do think this design would be capable of throwing a 5 lb pumpkin 200 yards. The drop towers should be made stronger, because the CW weight needed to throw a projectile weighing 5lbs a distance of 200 yds is going to be a lot. Right now, I'm making the towers stronger and lengthening the arm... although I haven't been working too diligently on that.
The arm would also have to be strengthened, as it may break with such a high load. (Maybe, I'm not sure) Rectangular aluminum tubing might work better than wood, but i can't vouch for that so don't take my word for it. It could be something to try, considering a hollow aluminum tube may also be lighter.
The sling lines would have to made of thicker rope and a better design for the pouch would have to be created.
as for the distance of 200 yards...if you optimize the CW/ projectile weight ratio and the short arm/long arm/sling length ratio, you may be able to throw a pumpkin 200 yards.
My design is by no means optimal, so I would recommend using it as a design template and not strict dimensions, especially for the arm and sling.
Other than that, you WILL need a thicker CW bolt. Depending on what weight you use, I would recommend something at least 1 1/4" to be on the safe side. (Just in case, that might be overkill. If anything, it will add weight to the CW.)
Reinforce the bolt holes, too.
If you have any other questions please ask me.
What is the total length of the arm with the extension? Moreover, would you recommend using said full length? Also, what diameter of carriage bolts should I use for the arm assembly? I'm guessing it should be thicker that the ones you used due to the (much) higher CW (around the lines of 500-600 lbs), but what would you recommend using?
frankenboom (author)  JediKnightTemplar3 years ago
Again, sorry for the late reply.
The total length of the arm with the extension was about 9 ft, 1 inch.
I would recommend using this full length, but make sure that the arm will be strong enough and light enough. The longer it is, the more important it is that the tip be light. If the rm is longer, the forces on it will also be larger.
For the arm assembly, I don't think the carriage bolts need to be necessarily thicker, as the object of them is to spread out the force over a larger area. If you make the short arm longer, just use more carriage bolts. Most of the force is taken by the plywood and 2X4s, so the shear force should be small. If you really want to be sure, just use more than you think you need. (Maybe 1/2"?) If anything, they'll add more weight.
Now, I'm pretty sure you're not talking about the counterweight bolt, but if you are, make yours VERY THICK
It should be hardened steel along the lines of 2 1/2" thick
Remember, some parts of the structure will probably have to be reinforced. (Especially the trigger system)
If you have any other questions please ask me.
good luck
koolaidman83 years ago
if i build it will it launch and about how far and dose it work well
frankenboom (author)  koolaidman83 years ago
If you build it correctly, then yes, it will launch. (should launch)
there are many factors which influence the success of each launch.
on this one, the pin was a nail with two heads. These ridges would catch on the ring, causing downward throws.
Or, the arm would hit the guide blocks on its way down, right before the wheels on the arm contacted the track. this made it throw backwards.
this trebuchet launched a baseball only 206 feet.
The trajectory, however, was way too steep (we had no idea where the baseball was until it came down) and the arm was too short.
It does work well and it can launch farther than 200 feet (probably around 400 with a lower trajectory) but it requires tweaking.
please comment if you need help.
hopefully you'll build it.
cool! Im planning on building one of these but much smaller to shoot golfballs!
frankenboom (author)  MrMadmonkey43 years ago
awesome!

with a smaller treb, you need to make sure the arm is extremely light so it can move quickly.
let me know how it goes!
Sure, it will hopefully be done in a week of two.
Is it possible to get a copy of the Sketchup files you had? I'm having a trebuchet contest and would like to do something similar.
frankenboom (author)  lastcoolnameleft3 years ago
Hi lastcoolnameleft. As much as I would love to tell you that I can get you a copy of the sketchup file rght away, I can't.
I'm on vacation right now (had no Internet for the past week, sorry it took me so long to respond to your comment) and I don't have access to the file. I might be able to get it in about a week from now. When do you need the plans?
If you need them before sunday, reply and. CN try getting them to you before then.
Best of luck in your contest!

I don't need them that quickly, as the competition isn't until September, but after you recuperate from your vacation, that would be great. We just build a "regular" small scale sized trebuchet this past week and are looking to progress towards a floating arm trebuchet next. Hope you're enjoying your trip!
frankenboom (author)  lastcoolnameleft3 years ago
O.K. I can't figure out how to post the file on the instructable.
if you have an email i can email it directly to you, unless you know by any chance how to post the sketchup file on the instructable.
otherwise, send your email address to my inbox. Don't put in in a comment or you might get spammed.
frankenboom (author)  lastcoolnameleft3 years ago
k, im going to try posting the sketchup file to the instructable. One note, on one of the diagonal supports, the faces are not there, its just a wire outline.
I'm not exactly sure why, but i havent been able to fix it.
There may be a few small errors in the sketchup version but they should be small, if any. It's been a little while since i last looked at it.
frankenboom (author)  lastcoolnameleft3 years ago
okay, good. I will probably be able to send you or post the sketchup file on monday. I can get my dad to bring the file saved on my computer. good luck with your trebuchet and PLEASE ask me any questions you may have.
Thanks
roliver-23 years ago
i am thinking about building one for a school project. How much counterweight did you use. I can use 200 lbs.
frankenboom (author)  roliver-23 years ago
200 pounds!!
wow...
If you're going to use this design, i would recommend being very careful with that weight...
Especially with the trigger...
I only used 50-60 ish pounds and the trebuchet has held up 100% ok...
No structural cracks or warping-
Remember, since the trigger is screwed directly onto the drop channels, you may need to thicken or reinforce the area where the eye bolts screw in--
Gradually add weight and test fire it several times with each weight.If you see anything go wrong, back off a bit.
Just be careful with that weight, check it after every fire.
Other than the trigger, the weakest part of the trebuchet is the CW bolt and axle.
-They need to be thickened if you're going to use 200 pounds.

One other guy (Gooches vfd) said the bottom of the drop channels cracked. Although it hasn't happened to me, add some reinforcement there too.

I got an A on my school project. With this, it's hard to go wrong.

Remember to add reinforcement, just in case.
PM me or comment if you need any help at all.
Good luck !
this may sound like a stupid question but what does a higher arm ratio actually mean. what has to be changed on the arm?
frankenboom (author)  roliver-23 years ago
Don't worry about stupid questions.
I'm sure I ask more than you.
well, it'll take a bit of time to fully explain.
Essentially, when you have a higher arm ratio, the short arm (the side with the counterweight) is much shorter than the long arm. (The side that the sling attaches to.)
So, we can think about the arm as a lever or a seesaw. When the short arm is much shorter than the long arm, a small movement on the short arm will be amplified on the long arm side. This effect is amplified as the ratio increases. Remember, as the ratio increases, the short arm gets shorter in comparison to the long arm.
So, a higher arm ratio will whip the arm faster, but more weight will be required becuase of the higher ratio.
Let's say we have a 2 to 1 ratio and a 3 to 1 ratio.
The 2 to 1 ratio means that the length of the short arm doubled (2) is the length of the long arm. (1)
A 3 to 1 ratio will have a short arm that is 1/3 the length of the long arm.
The wheel placement is what decides the ratio. The closer to the counterweight, the higher the ratio. The farther away from the counterweight, the lower the ratio.

A lower ratio requires less weight and can fling heavy objects better.
A higher ratio requires a bit more weight to fling something, but when it does the tip of the arm will move faster.

However, when the counterweight itself moves at the same speed in both ratios, the higher ratio will move the arm faster, but may require more weight to do so.
Remember, the ratio is decided by the wheel placement.

Experiment with different holes until you get the best distance for your payload and counterweight.

Hopefully that answers your question.
Please keep commenting- I like comments...
Let me know if you need more help!
Alright thanks, do the size of the wheels matter if you want more weight because the ones pictured here are small.
frankenboom (author)  roliver-23 years ago
Although the size of the wheels does not particularly matter, they should be at least 3.5 inches to easily roll over the gap in the tracks for the drop channel. If you are going to use a heavier counterweight and therefore a thicker bolt, you will need to make the drop gap wider. If you are going to make it wider, the wheels should be big enough to roll over it with the full weight of the counterweight and not get jammed.
Basically, the capacity matters more than the wheel size, but make sure the wheel size is right so that the arm rolls as smoothly as possible.


This website is a great one; it's where i bought my wheels: http://www.mandmsupplycasters.com/
My wheels can support 600 pounds if i remember correctly.
They have bearings, along with an adapter tube for the diameter of the bolt you will screw them on to.
And the best part is that each one was only 4$

that's dirt cheap for a wheel with bearings.
I would recommend getting around 5 inch-ish wheels and maybe 900 lb capacity with your weight, just to be safe.
my wheels are made of phenolic.
Remember: capacity is more important than size.
Get wheels rated way above your weight. A falling 200lb mass will exert more force on the wheels than 200 pounds, because of the speed the weight is moving at. The inertia and stuff...
good luck
GoochesVFD3 years ago
I have built a scaled down version of this, and forgot to put anything for the sling to travel through. However, I tied the sling short enough to just barely sit on the groung in the loaded position. I was able to get 150 feet with 50 lbs. of counterweight. I built and competed in two contests in a 3 week time span, and didnt' have too many practice shots. I will make some improvements to the design( seeing as the 2x4 where I cut the drop channel has cracked at the bottom) and try to post pics if you would like.
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