Homeschooling while working: How to build a trebuchet to teach maths, physics and fun

If you are homeschooling your children, as part of your working day, you may face challenges in holding their attention.

You can use a trebuchet to teach maths and physics, building itself is a project, and ultimately it throws things about, which is fun as seen here - https://www.linkedin.com/posts/activity-6653272817783619585-OPW

Building a trebuchet requires seven bits of wood, string, cloth and screws. You'll need a weight and projectiles, but everything else can be improvised. I made this from bits of old fence, and shaved a stick cut from a tree branch to make the dowelling.

If you want to give it a go this weekend, I've outlined my approach as guidance below.

Materials

• 2 x 110cm wooden bars with a square cross section for base frame (A x 2)
• 2 x 45 cm planks with good width to act as upright frame to hold the pivot of the trebuchet (B x 2)
• 2 x 30 cm planks to act as bracers to the upright frame (C x 2)
• 1 x dowelling rod to be the pivot of the trebuchet (D)
• 1 x 60 cm wooden bar to be the arm of the trebuchet (ensure its height is greater than the diameter of the dowelling) (E)
• Vice
• Lots of paracord / strong string
• Lots of screws
• Pencil
• A nail with a very small head (carpentry nail is good) (F)
• Drill with one bit that matches the dowelling’s diameter (Bit A) and another to match the screws’ diameter (Bit B)
• Round file
• Sandpaper
• Plastic plant pot (G) to hold the counterweight
• Projectiles of your choice
• Material cut into 5cm x 3 cm strips (H) to use for the sling

Instructions

Hold the two 45 cm planks (B) in the vice so they are completely aligned and drill a hole through them both with the drill bit A which matches the diameter of the dowelling.

Set the two 110cm wooden bars (A) so they are parallel with one another and the gap between them is less than the length of the dowelling (D).

Screw 1 x 30cm plank (C) towards one end of the wooden bars (Ax2) so they are fixed in place This will support the vertical frame, arm and pivot. The longer part of the arm (E) will have the longer length of frame under it (see final pic).

Place the two 45cm planks (B) into place vertically on the inside of the bars (A), and up against the 30cm plank that has been attached to the bars (C).

Screw the other 1 x 30cm plank across the bars to hold them in place (C).

Screw the 45cm planks (B) in place.

Mark 10 cm lengths along the 60cm bar (E) with a pencil

At the 20 cm mark on the 60 cm bar (E) drill a hole with the drill bit A which matches the diameter of the dowelling.

Push the dowelling (D) through the first vertical plank (B) then through the hole in the arm (E) then through the other vertical plank (B) so that the arm is now held by the dowelling.

Mark 5cm between the 20cm mark (over the dowelling) along the arm (E) and the 10cm mark, then with the round file, make a groove. This will be used to the hold that string that supports the counterweight.

At the other end of the arm (E) put a screw into the side of the wood, and hammer in the nail (F) into the *end* of the arm.

Make two holes in a piece of material (H), take two pieces of string cut to 30 cm long, feed them through the holes in the material, and tie a knot in each so the knots stop the string from passing any further through the material.

Put a slipknot at the other end of each piece of string. Loop one around the screw and loop the other over the nail. When the trebuchet swings the sling, this knot will slip off the nail to throw the projectile.

Take the plant pot (G), make a hole in each side and feed string through – the length will need to be such that when the mechanism swings, the plant pot can swing around under the dowelling. Tie knots in the string to prevent it from slipping out of the plastic. The pot will be used to hold the counterweight.

To make the counterweight, you can use any heavy metal items that you can hold in the pot, the heavier the better.

Having filled the pot with weight, hold down the long arm so the weight is suspended, put a projectile of your choice into the sling, making sure the string is over the nail, then release to fire the projectile.

We fired 2cm x 2cm blocks of wood anywhere between 1 and 6 metres, depending upon the weight, length of the arm and the length of the string on the sling, as seen in the link below:

Firing the trebuchet

Advanced manufacture

To keep the dowelling in place between the upright frames I drilled small holes at each end and put nails through, which could be removed from the dowelling.

To increase the weight we could use – and increasing the weight significantly improves range, power and accuracy – I built a wooden platform out of a piece of oak that was able to support two splitting wedges, still suspended by paracord.

Maths

As trebuchets are not consistent in their throwing, we calculated the average distance thrown, and then worked out the best place to fire from on that basis. To help your kids’ education, in addition to the measuring and construction, working out averages, you can change the weights of projectiles and counterweight, and the dimensions of the arm and sling, to see what effect they have.

I also built three different length arms to adjust and had the kids look at the effect that had on distance & height. I also made a sling with 10cm longer string for the same purpose. By building the stronger weight platform I was able to adjust weights more effectively so that is recommended.