Introduction: The Curiously Strong Trebuchet: a Pocket Sized Medieval Siege Engine

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The Curiously Strong Trebuchet is a miniature trebuchet designed in a way such that it can be disassembled and stored in an Altoids tin. It uses standard materials like wood, threaded metal rods, and other hardware. It also uses common tools most every hobbyist would have in their garage. For these reasons, The Curiously Strong Trebuchet would be a great weekend project.

According to Wikipedia "a trebuchet works by using the mechanical advantage principle of leverage to propel a stone or other projectile much farther and more accurately than a catapult, which swings off the ground. The sling and the arm swing up to the vertical position, where, usually assisted by a hook, one end of the sling releases, propelling the projectile towards the target with great force."

My trebuchet is a bit different than some of the others that you see, in that uses a rubber band instead of a counterweight. I opted for rubber bands because they gave me better results with this particular trebuchet than weights and they are much more compact. This kind of siege engine is called a spring trebuchet, a form of a torsion trebuchet.

Here are some links, in case you want to get some more background info before you start:

NOTE: The measurements in the steps ahead assume you are using an Altoids tin, or any other container of the same size.


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Step 1: Parts and Tools

You will need the following in order to build the curiously strong trebuchet.

X2 -#10-24 tee nut
X3 -#6-32 round head slotted screw
X3 -#6-32 machine screw nut
X2 -#10-24 rod coupling nut
X1 -#10-24 threaded metal rod (should be about a foot long)
X1 -Altoids tin
X1 -String
X1 -Cheerios
X1 -Rectangular stick of good quality wood (I used poplar)
X1 -An assortment of sizes and strengths of rubber bands
X1 -Straightened coat hanger or other wire
X1 -Standard rubber aquarium tubing (make sure that it's a snug, but not tight fit over the machine screws)

-5-minute epoxy
-Tin snips
-Cordless/electric drill and drill bits (a cordless drill will suffice for most of this project, but an electric drill really speeds up some processes)
-Hacksaw/bolt cutter (again, a hacksaw will suffice, but a bolt cutter will work better)
-An assortment of pliers
-Dremel tool
-Center Punch
-Heavy hammer
-Coping saw
-Diagonal cutters

Step 2: Cut Rods and Screws to Length

Using a hacksaw or bolt cutter, cut two 3.5 inch sections of #10-24 threaded rod. Next, cut the head off of a #6-32 machine screw. This should end up being 2.75 inches long. Finally, cut a 1.5 inch and a 2.5 inch section of 2 #6-32 machine screw. Both parts should include the heads. Set these aside.

Tool Tip:
Bolt cutters give you a very clean edge on the rod/screw, but they require quite a bit of hand strength to use. Here is one easy way to avoid hurting yourself (or spending hours on one cut):
First, screw the threaded rod or screw into the bolt cutter, as shown in the second picture. If the rod/screw is really long, lightly (so you don't ruin the threads) fasten it in the chuck of a drill, make sure the drill is on the right setting, and slowly pull the trigger.
Next, put the handle into a vice (as shown in the third picture) and start clamping down handle, thus cutting the rod/screw.
This method gives you just as good results as if you did it by hand, with a fraction of the effort.

Step 3: Cut and Drill Wood Block

First, cut a piece of wood to 1.25 x .25 x .75 inches. Then, drill one hole with a 1/8 inch bit and another hole with a 9/64 inch bit straight through the center in the manner shown below. On the 1/8 inch hole, you will need to wiggle the drill around a little bit to make it slightly bigger than 1/8 inch.

Step 4: Drill Holes in Couplers

First, draw a dot with a Sharpie 2/3 of the way up from the bottom of the bottom of both couplers, in the center of one of the hexagonal flats (see first picture). Next, set the coupler on an anvil (or on any other surface you don't mind banging on really hard) and tap a small indentation on the dot with the center punch. Put some oil in the hole, and clamp it into the vise. Using a electric drill (you could use a cordless, but it goes really slow), drill straight through to the coupler. Repeat these steps with the other coupler. They are never going to be perfect so just try your best. They should look like the second picture when you are finished.

Step 5: Cut and Bend Hook

This step, undoubtedly has the biggest effect on the functionality of the trebuchet. You probably won't get the exact angle of the hook right the first time, so you will have to adjust this later on.

First, cut a 1.5 inch piece of coat hanger using diagonal cutters. Then, bend up a 3/8 inch section on the end at about 135 degrees. It should now look like the hook in the picture. The accuracy of the angle isn't critical at this point because you will need to make adjustments to it in step 11.

Step 6: Cut Rubber Tubing

For this step, simply cut two 5/8 inch sections of rubber tubing and one 1 inch section. You don't need to be too accurate with this step because everything is going to have to be adjusted anyway.

Step 7: Bend and Cut Tee Nuts

First, bend down all 4 flaps on both of the tee nuts. Then, using a Dremel tool, cut off the top section of each of them, so they look like the the second picture.

Tool Tip:
I recommend wearing a long sleeve shirt or jacket when using a Dremel to cut metal, because the sparks can sting your arms, which distracts you from your work.

Step 8: Prepare the Case

First, use a 1/4 inch drill bit to drill two holes in the lid in the manner shown in the picture below (drill out the black circles). To make the wholes nice and clean, drill on top of a piece of scrap wood. Then, cut two small slits (about 3/16 of an inch deep) in the front of the bottom part of the tin spaced one inch apart. This means there should be one cut .5 inches to the right of the center point and one cut .5 inches to the left of the center point. Cut two slits in the same way on the back. Now, you should have two flaps: one on the front and one on the back. Fold the flaps inwards with a pair of pliers and crimp them flat to the inside of the tin. The bottom of the tin should now look like the second picture.

Step 9: Assemble

Now that you have all the parts ready, it's time to assemble. First, we will need to glue the tee nuts into the case with epoxy so that the flat edges of the nuts face the outer edges of the lid (if this doesn't make sense, look at the first picture). Be very generous with epoxy to make sure they stay in. All the weight of the trebuchet and rubber band is focused on these two tee nuts, so they need to be structurally sound. After I applied the epoxy, I used small spring clamps to keep the nuts in place. Next, insert the end of the hook into the 1 inch section of tubing. Screw in the 2.75 inch screw into the other end of the tubing. I found that using a cordless drill to do this made it much easier. The hook and screw assembly (from now on, I will call this the arm) should now look like the second picture. Now screw the arm a little less that half way into one of the smaller holes on the wood block. Put two nuts onto the 1.5 inch screw, then screw that a little less that half way into the hole opposite the arm. You should now have something similar to the object in the third picture. Then, screw the couplers on to the 3.5 inch rods so you can still see through the drilled holes. Screw both of these into the tee nuts protruding through the top of the case. Finally, feed the screw through the first coupler, then the 5/8 inch piece of rubber tubing, then the arm assembly with the wood block, then the other piece of 5/8 inch tubing, then the other coupler. Put a nut on the end to ensure that it won't come apart and hook a rubber band around the bottom of the container and then in between the two nuts on the arm assembly. You should now have the completed trebuchet (picture 4). When you disassemble this, you don't have to reduce it down into individual parts: you can keep some things together, as long as it fits in the container.

Step 10: Ammo

For ammo, I used two Cheerios tied together with a loop on the end, as shown in the picture. You could use any other small, light object, but Cheerios are really easy to tie a string to.

Step 11: Test and Adjust

Congratulations! You have completed building The Curiously Strong Trebuchet! Now it's time to test and adjust. Watch the video in the next step to learn how to fire the trebuchet. Chances are, its either going to smack the ammo on the ground, or launch it backwards. This is an easy fix. If it releases too late (straight into the ground), you need to make the angle of the hook greater. If it releases too early (straight into the air), you need to make the angle of the hook smaller. Most likely, after you adjust the angle of the hook, it will fire pretty consistently, but if there are any other problems, you can either fiddle around with different lengths and angles, or research it online.

Step 12: Lights! Camera! Action!

Attached is a short video of The Curiously Strong Trebuchet in action. I don't believe you have to download it if your web browser can open videos.

Step 13: Wrap-up

Trebuchets are truly amazing because there are so many kinds and varieties of them. Make your Curiously Strong Trebuchet your own. Expand on it! You could add a really cool remote firing mechanism, add a tiny camera or laser pointer so you can see where you are aming, or even make it steampunk! The possibilities are endless! Have fun with it.

I'd like to thank Scissorman, the author of the Instructable found here. His Instructable (the Office Supplies Trebuchet) got me interested in trebuchets and inspired me to make The Curiously Strong Trebuchet.

Thank you for reading my Instructable and remember to vote for me in the Pocket Sized Contest if you liked it!

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