In this instructable, I'll show you how to make your very own Trebuchet. Mind you, this is technically NOT a trebuchet because it uses a rubberband to fire, but it can be adapted for weight. I attempted to use weight on mine, but found that the spring worked much more impressively then the weights did.
Materials you'll need for this...
1: Wood: 19 inch 1X4" plank for support arms, 13 by 9 inch 1X9" thick plank for the base, roughly 22 inch 1X4" plank for the firing arm
2: PVC pipe, 3/4" type, roughly 9.5" long.
3: Screws: standard wood
4: Superglue (optional)
5: Steel chicken wire, or make your own basket out of string
6: String/parachute cord (string recommended)
7: Weight (optional)
8: Spring: rubber band (optional)
9: Some kind of saw to cut the wood with.
10: Pipe cutter.
11: Steel pipe in place of PVC if you have it lying around.
12: Drill or screwdriver (drill recommended)
13: Wood drilling bits the same diameter as the pipe
14: Wood Peg (optional. I'll explain this one later)
15: Zip-ties (recommended for smaller tasks)
If built correctly/tuned correctly, the little trebuchet (or microtreb as it's known in my trade) can fling projectiles over dizzying distances with the slightest pull. My own version can throw a golf-ball about 18 feet on average, but with a little extra "oomph", we've gotten it to fire up to 22.5 feet in a single throw.
*DISCLAIMER*: use at your own risk. We are not responsible for injuries during construction or during play with catapult. Not recommended for children under 10.
Step 1: Base Construction
The first step is to simply build the base. Cut out a 9X13 inch base, or longer (15-17 inches recommended if you can spare the wood) for more stability. Once the base is cut, I recommend marking it so you won't confuse it for anything else you have lying around.
The base is a very crucial part, considering it has to support whatever you're flinging. I recommend plywood rather then particle board (PB may snap due to the load stress of your projectile.)
Step 2: The Support Arms
The support arms are next (we're building this from the ground up you know.) Cut out 9.5X4" arms from 1X4 planks of wood (thicker wood works too, but is not necessary). Next, drill a hole the exact diameter of the PVC/steel pipe, if not a little larger so the axle can fit through. DO NOT FIT THE AXLE THROUGH YET! It's recommended that you drill the holes before attaching the arms to the base, since it makes the construction a little bit easier from here on.
Next, use screws to secure the arms from the bottom of the base. drill up through the base and into the arms. The holes MUST be at the top of the planks, farthest from the base. Be careful of wood splits!
Please measure carefully! You don't want to be like me and drill too small of a hole (remember that if you're using 1/4" PVC that the quarter inch part is the diameter of the inside of the pipe. You have to measure the outside by yourself!)
Step 3: The Firing Arm
Cut out your firing arm from a similar 1X4" plank of wood (make it roughly 22-24 inches long). Drill a hole where you want the axle to go in the plank. Remember you need clearance at the bottom so your arm doesn't hit the base! Now we have 2 options.
The steps I've written so far work for a spring powered version of the trebuchet (though technically not a Trebuchet but rather a catapult). If you want to use weights, you'll have to drill the hole for the axle a lot closer to the base to give your weights some clearance! For the spring version, drive in a screw at the very bottom of the base, as well as one towards the designated front of your catapult. You'll have to attach the spring later. I'm also afraid you're going to have to figure out the weight system yourself! I recommend steel weights since they aren't as dangerous as lead weights.
at the other end of the arm, drive in another screw at an angle so only one side of the circular top sticks out at an angle. This is the slip hook, or the part that let's go of the basket so the catapult/trebuchet can fire.
Drive in a third screw below the slip hook about halfway. Do not drill it in all the way yet!
This finishes the construction of the arm. Now we move onto the axle.
Step 4: The Axle
The axle is one of the most crucial parts, and by far the easiest. I recommend you use the super glue or the wooden peg (I used both) that I mentioned at the title page.
slide the PVC or steel pipe (your choice) through the holes you drilled in the top of the support arms. Before you secure the axle, put the axle through the hole in the firing arm as well.
Now glue the axle into place at the support arms. DO NOT GLUE THE FIRING ARM! I recommend you use screws to keep the firing arm in place. Drive the screws into the PVC pipe, rather then the firing arm.
If you're short on glue, use the wooden peg/pegs by pushing them between the axle and the interior of the support arm holes until the axle is firmly in place. If you're like me, do both this and use the glue to have a firm support.
Once this is all in place, it's time to move onto the basket construction.
Step 5: The Basket
I recommend chicken wire for this step since it's easiest, but you do have the choice to make you're own basket if you really want the model to be that historically accurate.
Bend the chicken wire to suit your basket style or need. I went for a simple "rowboat" shaped design, which allows spherical projectiles to roll out simply and easily.
If you really want it to behave like a catapult, you can use a simple bucket firmly attached to the top of the arm, though this will more then likely decrease your range since the swinging motion of the basket adds to its power.
You can either choose to glue your basket together or to use zip-ties. I chose the second approach.
Now, tie the string/parachute cord/rope to the basket at one end and the other end to the half-driven-in screw from the previous steps. Make a second string leading from your basket to a simple loop.
We're almost done! Now it's time for some finishing steps before you get to start firing this puppy!
Step 6: Finishing Touches
Make sure the slip hook works just fine with a few test fires using the rubber-band spring. If you want to use metal springs, you can, though I found this hard to do.
If you want to (though I don't recommend it) you can choose to paint your catapult. I don't recommend this simply because the paint will more then likely add to the friction between the axle and firing arm. If you want to, you can also bunch up several rubber bands at once and use that for a spring, though this too isn't recommended because it can often lead to rubber bands snapping violently.
Now it's time to fire!
Step 7: Firing/ After Thoughts
To fire the catapult/trebuchet, hook the loop on to the slip hook at the top of the firing arm and hold the basket steady. Place your chosen projectile (I.E. golf balls, tennis balls, super-bounce balls, mentos, walnuts, etc.) into the basket, and pull it to the ground. If the base starts to rise, try holding it in place.
Make sure your head and body are clear of the arm, and let the basket go. If done correctly, the loop should slip off of the slip hook at a certain point and send your projectile firing.
KNOWN ISSUES: Some issues I've found during construction and ways to fix them.
Projectile gets stuck: make sure basket is open enough to fire projectile, or that there are no sharp edges on chicken wire.
Projectile simply slams into the ground: Your strings are too long and will often get snagged on either the firing hook or the securing hook. Shorten the strings, but not to much!
Catapult axle breaks: Try loosening the spring... and of course get a new axle!
Base breaks: Consider a stronger material...
Projectile goes 90 degrees vertically, but doesn't go forward: I've had this occur on numerous occasions with tennis balls, and truthfully have no solution other then to try a different projectile.
Slip Rope doesn't slip: Your slip hook might be too long and getting stuck. Try screwing in the screw further, or making the loop larger.
"Where Innovation meets Practicality: The FMC"