Building A Trebuchet Basics

treb2Building a trebuchet is less complicated than it might first seem. Sure, there are specific formulas and software programs that can crank out optimal performance trebuchet designs. However, I know builders who can estimate dimensions, cut out and then assemble their trebuchet hurling machines quickly without the aid of high-tech software analysis. Their trebuchets also perform with amazing distance, accuracy, and consistency. In this short article we will examine key elements to build in the proper sequence and in the proper scale [or relationship] to other components of the final working machine. Don’t be intimidated, it’s really not rocket science.

For most trebuchet enthusiasts, the fun of “hurling” is also in the designing, constructing and modifying of these amazing models. So let’s take a look at the key elements of building a trebuchet.

The base of a trebuchet must support the glide track, tower frame, and swing arm lever. The trebuchet base is typically attached to the glide track [board] upon which the sling harness will slide. There is no absolute formula for designing a trebuchet base. In fact, they come in a myriad of sizes, both in width and length. However, I have found that reliability and consistency is produced when the length of the base is 75-80% of the length of a swing arm (lever). Another good rule of thumb is that the width of the base should be about one-third of its’ length.

The base should be designed with the tower width and counterweight size in mind, since the size of the weight or box will need to swing through without interference. If the attached weight or box is wider than the support [tower] frame it will not pass down and through as it should…unimpaired.

Glide Track [board]:
This is the surface upon which the sling harness slides after the trebuchet trigger is activated. In most cases, the glide path is about three-fourths (3/4) the length of the base. When the swing arm lever is released the attached sling is drawn along the glide path and then whipped upward in an arc path until the cradle holding a projectile opens and releases it.

Tower Support Frame:
When building a trebuchet the tower frame is generally about 3/4 the length of the base. For instance, if the base measures 40 inches, a good tower frame height would be 32 inches. Again, these are approximations. The width between the tower primary support beams will depend greatly upon the type and size of weight planned for use. You will need to decide what size and the weight of an object to throw, and then select the appropriate weight(s) to use. Counterweights should be “approximately” 75-100 times the weight of the projectile.

Swing Arm Lever:
The primary swing board is commonly referred to as a swing arm lever, but some will call it a long arm lever or long arm beam. The swing arm lever works well when it is 1.4 – 1.6 times the base length. So, if the base board length is 3 feet, the swing arm lever could range from 50 inches to 58 inches. This will depend upon the builder and certain other adjustments that can be made, but I would tend to lean to the shorter side…probably choosing a 54 inch length (1.5 x).

The counterweight will ultimately determine the height and/or distance that a projectile will potentially fly. As indicated above, a counterweight that is 80-100 times heavier than the projectile will generally produce optimal results. However, understand that all other features of the trebuchet can serve to enhance or diminish overall performance. For instance, if the swing arm is too short or too long the trebuchet results may be limited.

Sling [harness]:
The sling is attached to the long end of the swing arm lever. It is connected by rope, string or cable to a cradle or pouch holding the object to be “hurled”. The sling harness length should be approximately 3/4 of the glide board. The sling harness should be designed to open and release the object in the cradle or pouch when it reaches the precipice of the launch path. This will depend upon whether one of the sling ropes is attached by a prong or in a slot cut at the end of the swing arm lever. Each trebuchet may have a slightly different release design.

Although not precise calculations used by all trebuchet builders, these primary features of a trebuchet will be useful for any novice trebuchet enthusiast. Understanding the essentail design components should also help you with the building a trebuchet basics.

Trebuchet Building Features

TrebCounterPrimary Lever = Throwing arm; also called the swing arm. Has what are considered long and short ends based on the relationship to the pivot position connected to the tower frame. The long end should be 3-5 four times longer than the short end and it should be strong but light. Sufficient to hold the counterweight but yet light. Don’t try to make the board longer with the intent to increase distance…that’s not how it works. The key will be to enable the trebuchet counterweight to swing through quickly for optimal hurling distance.

Sling = A good rule of thumb is to begin with the sling harness approximately 3/4 the length of the upper (longer) end of the beam and trial for optimal trajectory. The sling length will influence projectile trajectory, causing an object to too fly high, too forward, or even backward.

Counterweight = Weight about 80 to 100 times as much as the projectile to be hurled. It can be a fixed or a free moving weight affixed to the swing arm lever (beam).

Base = Foundation on which to construct the glide track and support frame pieces. The base should be designed and constructed to firmly hold together the structure during the “whipping” transfer of energy from the release of the beam (swing arm lever) that allows the force of gravity to draw the counterweight down. It is a sudden and powerful transfer that can sometimes be offset by adding wheels to the base. 

Frame = Is essentially the primary 2 side tower beams braced by supporting pieces. The height of the axle pivot point should be set so that the trebuchet swing beam is positioned about 45° when cocked and secured in the firing position. The attached counterweight should clear the tower frame sides, as well as, the “glide” or sling platform base when it travels down and through. There is an array of other terminology used in the design and building of the trebuchet, but these are the primary features that distinguish the trebuchet from other “hurling” machines (models). Discover how to easily and quickly build your own trebuchet, visit  How To make A trebuchet  to get access to free plans and more on key trebuchet building features.

What Is A Trebuchet?

Trebuchet45A Trebuchet is a horn-like instrument still used by herdsmen high in the Swiss  Alps to draw mountain goats toward cliff edges during hunting season. Okay, that’s complete fiction.  Although “trebuchet” may lend itself  to a European sounding term, it is certainly not a musical instrument?

Actually, the trebuchet is a machine designed using essentially the natural forces of gravity, centrifugal force, and leverage to perform unique engineering “hurling” magic. It has evolved from a medieval siege weapon used by the Romans to a popular device whom many refer to as a “toy for big kids”. A trebuchet machine requires no batteries, no fossil fuel, wind or water and is built by woodworking and engineering enthusiasts from all ages and walks of life throughout the world.

The trebuchet is basically a lever device that can be built with basic materials, many of which can be found in the home. The trebuchet uses a controlled weight and the force of gravity upon the weight, and when triggered, a lever arm transfers natural energy to generate amazing throwing power. Essentially, when a controlled weight is released at a specific height it displaces static energy to form kinetic energy. When this energy is redirected to a “sling”, it will ultimately launch varying objects hundreds of feet or yards.

Centrifugal force also plays an important role in the performance of a trebuchet. Imagine throwing a baseball or football. The trebuchet sling operates in a similar motion. You start the throw with the ball in your hand and then extend it backward behind your head and shoulders, gradually returning the ball with hand and arms forward and to release. Although not identical, a similar motion occurs with the trebuchet. The throwing object starts in one position and when activated, the projectile will slide along a track or board surface. As the swing arm pulls the sling harness skyward, the projectile will follow the path of an arc. One end of the sling must open at the apex, releasing the projectile and allowing it to launch skyward.

It’s not uncommon for new trebuchet builders to initially make the mistake of placing the release prong (headless nail) or slot at an improper angle. This can cause the trebuchet sling to release and open prematurely or too late, and affect the launch distance and trajectory. Another key feature of the sling is that one end should be permitted to release (open) at just the right time. A headless nail or prong, or a angle cut at the end of a swing arm should be adjusted to ensure a proper release and preferred flight trajectory. As the sling end (projectile) approaches a vertical position, one sling end should slide off an end prong (or out of a sling arm “end slot”) to complete a successful toss.

Trebuchet designs range from paperclip to piano slinging models, and perhaps one of the most popular models is available for free. You can find a quality fr-ee backyard plan at the “How To Make A Trebuchet” website. My teenage son found it, ordered it, and had hours of fun building it and enjoying it with his friends.  That’s a trebuchet .

How to Build a Trebuchet


 The trebuchet and catapult were amazing  
 weapons in their day and both were the
 basic siege artillery used to destroy castle  
 walls. Still, the trebuchet was generally the
 heaviest siege artillery and was often 
 referred to as the “Big Bertha”. Not 
 surprisingly, there’s a good chance this is
 when the phrase “Big Bertha” took front and center.  In all likelihood it was for good reason…it took substantial effort to build a trebuchet and it stood as a very imposing structure when completed.

Trebuchets were either a fixed counterweight or a free counterweight design. On the ancient trebuchets, a swinging bucket (free counterweight) allowed the weight to fall more vertically enabling more time for the increased force of gravity. This was more efficient in converting the energy from a vertical drop into the rotational motion of a throw.

The trebuchet also differed from other siege engines of the day because it did not rely on twisting or bending to generate its power. Whereas to build and hurl objects with a catapult, mangonel or ballista required serious, repeated twisting of heavy rope, the trebuchet used a heavy timber swing beam that pivoted on an axle mounted between two tall timber frames (i.e. a lever). The tower frames were secured by timbers attached to a base platform upon which the projectile to be thrown would initially slide before its free flight release. A sling harness with projectile cradle was attached to the swing beam’s longer end; and suspended from its opposite (upper) end was an enormous heavy wooden box filled with stones or sand (counterweight).

After the sling harness was fitted to the beam, the swing arm was drawn downward by a block and tackle and windlass until it was beyond a horizontal position. At that point the swing arm was secured into position until ready for firing. When ready, a trigger device was used to release the swing arm. This action caused the weight of the box of stones to snap the beam upright, pulling the sling and cradle harness along the base board and then quickly whipping the cradle upward in an arc path until it opened and hurled the projectile high in the air…and hopefully towards the target.

Fixed counterweight trebuchets do not have a bucket. Instead, they operate with only a heavy weight attached to the end. The Romans used heavy rope to secure the weight assembly to the swing arm beam. The falling motion of the counterweight tends to topple the trebuchet so wheels serve to counter this force. As the counterweight falls the trebuchet machine rolls forward, permitting the counterweight to fall more vertically.

Following significant technology advancement, more modern trebuchet designs now deliver an even more efficient transfer of weight and generate far more power. One engineering marvel is called the “fulcrum on wheels” design. It uses a counterweight that releases directly downward along a wheel track. Too bad for the great pillagers and attacking commanders of the medieval times…they would have loved such a Trebuchet design.

If you would like to learn how to build your own personal model trebuchet quickly and easily, visit the How To Make A Trebuchet  website order page. They offer one of the most popular backyard trebuchet models online, along with step-by-step video plans and instruction that even a novice can follow for Fr-ee. From A-Z, their plans show you how to have hours and hours of fun in building a relaible trebuchet.

Toys That Are Not Toys…Trebuchets

treb01The average person knows relatively little about a trebuchet or a catapult, or that both are ancient weapons that are becoming increasingly popular among engineering students, scouts and general woodworking enthusiasts.

Trebuchets and catapults were actively used as siege weapons during midevel times. Armies would design and construct these mystical, yet dynamic devices for obliterating enemy castles or fortress walls, and to launch rotting animal carcass’ over enemy walls to spread disease among those hunkered within. Today, scaled down model trebuchets and catapults are primarily built for fun and recreation by people from all ages and all walks of life. 

Pronounced “treb oo shay”, trebuchets comes in many sizes, from as small as a few inches to well over 30 feet in height.  Larger trebuchets have launched cars and pianos hundreds of feet through the air while the smaller designs have become far more popular. They are more practical for enthusiasts and can be constructed relatively quickly with materials and tools found in home improvement and lumber stores, or in many home workshops.

Not surprisingly, trebuchet building activity and design plans are becoming more prominent than ever before. Plans come in a variety of assortments. The joy of building and launching these unique devices has led to an assortment  of creative and effective designs. For the most part they are fun and safe; however, they can also cause damage or injury if operated improperly or without adequate safety precautions.  

Plans can be purchased online, some of which are available for free. However, the better and more complete plans will cost money. A popular trebuchet design package that includes rare video instruction can be found at the “HowToMakeATrebuchet” website order page. This site offers both a very popular “backyard” design plan with rare personalized video assembly instruction at NO Cost. The designer takes builders step-by-step through the entire construction. A youngster building their first trebuchet project will find this instruction particularly helpful over standard blueprint only plans. Moreover, the trebuchet design package is at a price anyone can afford. The design package is offered at an incredibly low price or for free, depending upon whether one prefers a physical copy of the material or only online access.

Perhaps one of the most ideal projects for kids, family and adults is the building of model trebuchets or catapults. Trebuchet projects ideally bridge the sensations of joy and danger like no other project for youngsters or adults. Although more commonly used today like “toys”, they are still trebuchets.

Trebuchet Model 309 – Build sequence

HOW TO MAKE A TREBUCHET – Treb 309  Build Sequence

Safety – Priority – Watch safety video First…before construction and apply safe operating principles throughout the construction and use of the trebuchet.

Pre-construction Steps:

1 – Gather recommended tools

2 – Assemble the supplies/materials needed

3 – Review written plan instructions and drawings

4 – Measure and then cut board sections according to materials list specifications.  (note: be sure to mark each with corresponding code)

5 – Watch Construction and Assembly Sequence in the Fr-ee instructional Videos:

Operation Tips:

Ensure that trebuchet is stable and on flat surface

Always practice safety procedures (use front and rear safety pin)

Mark firing end prominently for all to see (possibly with red tape)

Ensure that no one or object is in front or behind the swing arm just prior to release

Keep your head and person away from swing arm at all times

Ensure that the projectile will not reach or cause harm to persons or things

Never launch  sharp or explosive objects from Trebuchet Model 309.