3D Designed Trebuchet

This is a 3D modelled trebuchet using the fundamentals of mechanisms. It also comprises some woodwork and is a good project to do to learn a variety of skills to help you on your skillset.

3D printing machine

Fusion 360/ Tinkercad (to design)

7mm Pine wood sticks

Laser cutter (3mm thin wood slabs may also suffice, as its for 2 rectangular slabs)

Weight

Kebab sticks

String

UHU glue

1/8" Dowel (Kebab sticks)

Wood Glue

Tools

Ruler

Writing Tool

Hacksaw

Drill

Sanding tools (sand paper)

I would recommend using fusion for this step. I have attached a few different softwares depending on if you have shapr or fusion, download the .stl for shapr (fusion may also work) and .f3d for fusion. If none of those work, or you want to design it yourself please refer to my description for the different parts I had constructed to design this trebuchet.

For the thickness of the Material I would recommend 10x10mm

The design/parts used are as follows:

2 Short Diagonal Braces (15mm shorter side, 25-30 mm longer side (depending on angle and what fits))

4 Long Diagonal Braces (75mm longer side, 50mm shorter side)

2 Frame Extension Rails (80mm short side, 120mm longer side)

2 Short Frame Sides (125 mm length)

2 Uprights (100mm length)

2 Long Frame Sides (150mm length)

1 Frame Crossmember (175mm length)

Print the 3D design it, for a 3D design it is quite big but it works as a good trebuchet. Make sure to make 2 holes on both of the uprights, of about 4mm in diameter so that the kebab stick can fit in quite nice.

2 Lower arms (60mm length , Made from Wood for the launcher)

1 Upper Arm (190 mm length, made from wood for the launcher)

Slabs of wood, approx. 26 and 29mm each made from mdf (or you can use whatever wood that floats your boat, not too thick though around 3mm)

Instructions

Use the UHU Glue to stick the slabs of wood onto the 2 indents , making sure that it stays inside the frame like in the picture acting as a base for when you pull your trebuchet back

Glue the Lower arms to the upper arms, making the both parallel and about 25mm behind from the Upper arm so it looks like in the image. Glue it using Gorilla Wood Glue, though UHU and hot glue may also suffice.

Drilling is also important to do, so make sure to drill a hole in the middle of the gap of the 2 Lower arms on one near the middle including the upper arms. Use a 4mm drill while drilling.

Now take a long kebab stick and you will need to cut it into 2 parts. You will need about 190mm of length in total, with ones length being 145-150mm approx. and at least 35mm for the other one.

Using the Kebab Sticks put the long one through one of the holes in the trebuchet frame, and put the shorter kebab stick through the place with the holes only with the lower arm, and put a weight in the middle so that the mechanical advantage will allow for you to fling objects with the trebuchet, which is the whole point of a trebuchet.

Next, you will need something hook-like, and small. You can be creative and innovative like myself, as I did not have one and instead used a safety pin which I cut so that it was like a short metal toothpick. you then stick that into the launcher on the end where it is just the longer arm and stick it in at an angle.

Get some string about 210mm long, tie a knot near the end and put the knot onto the 'hook'. Put the Arm onto the main frame of the trebuchet through the kebab stick going on the top and make sure you put it the right way.

If you follow all those steps, you should have a functional trebuchet. I used a paperclip to demonstrate, but you can put other things if you want. Just remember to up the weight if you do, so that the trebuchet has enough Mechanical Advantage to launch the thing. Enjoy!