Introduction: Making the Frame and Arm for a Trebuchet (Partial Project)

Me and my friend wanted to make a trebuchet, so here's what we got.

(For some reason or the other i stopped taking pictures half way through, but I'll try and explain what else I did.)

Step 1: Planning

We looked around on the internet and found some pretty heavy math involved in the building of a trebuchet (more than we liked to get into at least) and we found some plans for "desktop trebuchets" but we wanted something a bit bigger. We didnt do much planning except looking at other models and different peoples takes on how to build one, so this isn't perfect by any means, but it worked for us. Hopefully we could get some new ideas and maybe help other people get a basic idea on how to build there own trebuchet.

Step 2: What You're Gona Need

We planned on wingin' our materials just like we did our plans, but we eventually decided that a trip to the hardware store would be necessary. We took a guess at how much of everything we would need, and this is what we got...

We purchased:

8- 2x4's,
1- 1 foot, 1/2 inch diameter bolt with two washers and a nut
1- 1/2 foot 5/16 inch diameter bolt with two washers and a nut

We also used a bunch of junk that I had lying around in my basement. You might need to purchase these items if you dont have them...

2- 2x2's
2- 25 lb. weights (from a benchpress)
Cloth for the sling pouch
Rope or chord of some type
Staple Gun
Wood Screws
A big washer
A finishing nail


A saw (a chop saw works best)
A drill/screwdriver
Drill bits

Like I said, we were wingin' this entire project so you might need to improvise here and there.

Step 3: Building the Frame

We decided to use an A-frame type structure to support our trebuchet. This is how we made all the cuts and put it together.(the pictures probably show you better than I could explain) You're gona need two of these "A-like" structures total, and they will eventually be attached to a base. You will also need to drill a 1/2 inch hole at the top of the A- frames, for the main axis. We put the hole about two inches down on the vertical piece of wood on the frame.

O yea...probably the most helpful thing you can use during your trebuchet construction is clamps. Even if you're working with friends, a good set of clamps are invaluable.

Step 4: Making the Base

We decided to make our trebuchet base 8 feet long, so it would provide some good stability. To make the base, all we did was connect the 2x4's with 8 inch pieces of 2x4 as shown.

Step 5: Aattaching the "A's" to the Base

To attach the A's to the base, we lined them up in the center of the base and used screws to fasten them together. The key part here is making sure that the holes for your axis line up, as shown in the picture.

Step 6: Building the Arm

For our trebuchet arm, we decided to use 3 pieces of 2x2. One section(the long portion of the arm)will be 4 feet long, while the other section(the short portion of the arm)will be made of 2 2x2's that are two feet in length each.

Holes need to be drilled similar to the places shown in the picture, for the axis, and also to hold the counterweights.

The ratios for the axis point and the center of the counterweight is 4:1, so if yo decide to use a 4 foot long arm the counterweight needs to be placed a foot behind axis.

When we tried to fit the counter weights inbetween the pieces of 2x2 they didnt fit, so we had to shave the insides off to allow them to fit nicely.

Note: The arm we constructed for our trebuchet wasn't exactly how it should have been according to the correct ratios. When constructing your own arm make sure that from the center of your counter weights to the main axis point is one foot long, while from your axis point to the end of the arm is four feet long. The long portion of our arm ended up being about 8 or so inches short because we didn't account for *this* (look at the second picture) section of the arm having to be connected to the other 2x2's.


kumarrockon made it!(author)2010-01-20

Love it!
I want to scale it down for a school project,
any suggestions?

corey_caffeine made it!(author)2009-07-02

I hope you realize the frame isn't near wide enough for a bucket of weights. however you could use barbell weight disks

BigCoCo made it!(author)2009-07-03

I never really intended to use "a bucket of weights" for this project. as you can see from my materials list and the picture in step 2, I used 2- 25 pound weights from a bench press. im not sure if thats what you meant by barbell weight disks, but they fit very well in the narrow gap provided by the frame.

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