How to Design the Perfect Trebuchet

Looking to lay siege to your neighbor's house? In this video, we'll teach you the basic design principles behind trebuchet construction.

(This video is purely for educational purposes, please do not lay siege to anything)

The trebuchet is one of the most famous siege engines of all time, and designing and optimizing the powerful machine involves some tedious work.

To understand how to optimize the design of a trebuchet, first we need to understand exactly what designs and principles make up one. A trebuchet in its most pure form involves a counterweight that falls completely along the vertical axis and a swing arm. Attached to the end of the swing arm is typically something like a sling to increase rotational velocity, but it isn’t essential to trebuchet design. Potential energy is stored in the lever mechanism as the large counterweight is lifted. Once dropped, the potential energy stored in the counterweight is transformed through linear motion into rotational kinetic energy for the projectile.

It’s important to note that no compound motion or mechanism is involved in the trebuchet, rather it is one simple lever arm along with a counterweight. Once the mechanism is understood, the variables to controlling flight begin to appear. Being such a simple design, the only things you can vary are the lever arm length, the height, the counterweight weight, and where to position the fulcrum along the lever arm. While the constraints may seem limiting, optimizing all of these factors can produce a highly efficient machine.

All images and videos courtesy of the creative commons or used in accordance with fair use laws.

Trebuchet animation courtesy of Handrox-G via VideoHive. Copyright information available upon request.

[FortInTheWoods]

This is much more informative than our video... Less breaking things, but much more informative.

[takaohasiguchi]

I feel like it's really a lost opportunity whenever you explain an element of the trebuchet but didn't actually show it on the screen, instead playing the default trebuchet shooting animation. For example: When talking about the arm length, you can lengthen or shorten the arm of the trebuchet, let it shoots, and see how the shot would be different with the change.

[MedievalTrebuchet]

At 1:12 minute-mark you say that there are only four things you can vary: "Lever arm length, height, counterweight weight, and fulcrum position." You are missing half! You can vary the counterweight height, the sling length, and the angle of the pin on the tip of the throwing arm, as well as the CG of the arm. The counterweight height is how far it hangs from the counterweight axle on the arm. A counterweight height of zero would imply a fixed counterweight. Ideally, you want the counterweight to hang as far down as possible without hitting the ground, but in the case of trebuchets like the one at Warwick the box has to clear the winding axle for the treadwheels. You can also vary the CG of the throwing arm by tapering it or adding "counterpoise" weight. Some medieval drawings feature an added ring of weight on the butt end of the throwing arm (in addition to the counterweight box), which was probably meant to bring the CG of the arm closer to the main axle even before the box was attached.

[aaronlatapi]

You uploaded the exact video i was looking for! You see I juste entered a contest of catapults. I thougt of trebuchets but i didnt know how to start building it until you. Thanks good cuality video

[kevd]

0:06 "Stop looking at our plans, woman. You don't even get a hard hat."

[curtismilligan]

So did I get this right? The ideal payload to counter weight length is 3.75:1, 4:1, or 5:1 and the ideal projectile mass to counterweight mass is either 1:75, 1:100, or 1:133. If so I need a bit more of a clear answer from this.

[ouchman]

putting the swinging fulcrum on wheels allows for a more direct vertical drop and increases force and velocity of projectile

[tbmike]

Maximizing potential energy is crucial. Construcing trebuchet so that the weight falls as vertically as possible, instead of swinging, increases efficiency. Wheeled trebuchet end up being the most efficient.

[mjstow]

Bloody brilliant. Just the info I was looking for. An easy subscribe.

[t.j.payeur]

All you need is one day in the field, equations, not so much...

[dv]

Exactly what I was looking for, great video

[Hambxne]

Depending on how long this quarantine lasts, I may just have to build a trebuchet and lob a fireball at my neighbors house on Wednesday May 6th at 5:32 AM EST..

[pavelmolodchik]

Can I please have the counterweight be perfectly motionless after the shot thus converting all its potential energy into the kinetic energy of the projectile? Or am I asking too much

[kraigthorne]

2:32 Donald B Siano is educated and ignorant. Everyone who knows anything at all about trebuchets knows that they need to have wheels!!! The wheels make it so all the kinetic energy of the counterweight can be used to move the projectile. If there are no wheels the extra kinetic energy will be absorbed by the trebuchet.

[boltonky]

Thanks, Great help for an upcoming project

[kraigthorne]

3:03 #4 the Trebuchet MUST have wheels.

[zarminehk]

Lol I love that part “it’s called Well you can read.”

[davidx]

Amazing….PARENTING! (Oh, and the trebuchet c’est très cool aussi!)

[breannestahlman]

I have aquestion:
How to take into account the elevation, let say that you shoot your trebuchet from an elevated site, how to calculate everything, is there some magic online to do that fast and easy?

[laurenoney]

"you can read" 😂 sass levels are high!