How To Build A Trebuchet

Drawing #1

Building Overview and Parts List

Now .....

Have you been paying attention?

http://library.thinkquest.org/05aug/00627/history.html

Click on the follow this link to take a quick quiz!

Please note: Once on the page, please go to the Trebuchet quiz tab along the left side of the page.

Drawing #2

Let's begin by collecting our materials for the build. You will need to have the materials cut to the specific lengths and dimensions in order to proceed with this trebuchet.

As you can see, the counterweight pivots around a much shorter distance than the payload end. The advantage of this is that the payload end of the beam reaches a much higher linear velocity than the counterweight end of the beam.

This is the principal of mechanical advantage, and is what allows the payload to reach a high launch velocity. However, because the counterweight pivots around a much shorter distance, its weight must be much greater than the weight of the payload, to get a high launch velocity.

However, increasing the mass of the counterweight beyond a certain point will not help, since the limiting speed of the falling counterweight is free-fall speed.

How did you do?

Throwing arm

All material is 3/4" softwood.

A - main base (1) - 9 cm x 30 cm

B - Base Supports (3) - 3.8 cm x 14 cm

C - Uprights (2) - 28 cm x 1.8 cm

D - braces (2) - 1.8 cm x 27.5 cm (long side, angle 45 degrees)

Are you ready to start building?

If so, let's continue on!

If not, you may want to go back and revisit some of the information.

How a Trebuchet Works!

We will be constructing a swinging counterweight trebuchet.

Trigger block

1.8 cm x 7.5 cm

1.8 cm slot cut in one end.

The trebuchet is actually two things- a lever and a sling.

A lever is a simple machine that gives a mechanical advantage when given a fulcrum, or pivot point.

It is often used to move heavy loads with less effort.

The Trebuchet is a first class lever. If you look at the diagram below, you see a first class lever.

Step 1

How To Build a Trebuchet

We will start with the counterweight basket.

The basic parts of a trebuchet include the frame (base), beam (arm), counter weight, sling and, of course, the projectile.

Looking at the pictures in the following slides, you should be able to see that the fulcrum, or pivot point is the place on the base where the arm (beam) balances.

How to Navigate the Presentation

1. Apply glue to both basket end pieces.

In order to navigate through this prezi you can do the following:

- Move your cursor to the bottom of the screen and two arrows will appear allowing you to move forward or backward within the presentation.

- If at anytime you wish to return to the main screen move your cursor to the right side of the screen and the home symbol will appear.

- From there you are able to move to any slide by simply clicking on top of that slide.

2. Align basket bottom piece with end pieces and nail in place with 1" common nails.

(Important: one of the end pieces has a slot cut in it to accommodate the arm. Make sure the longest part of the slot is on the outside of the basket.)

Types of Trebuchets

3. Apply glue to sides of end pieces and attach side plates with 1/2" #6 flat head screws.

History of the Trebuchet

A trebuchet is a type of catapult that works by using the energy of a raised counterweight to throw a projectile.

There are many different types of trebuchets that range is design. Some of the most commonly known are:

1) Fixed Counterweight on a Fixed Frame

2) Fixed Counterweight on a Floating Frame

3) Floating Arm Trebuchets

4) The Swinging Counterweight

One of the final improvements to reach the trebuchet was the "propped counterweight". The propped counterweight was very similar to the hinged counterweight, except the weight was forced to make an angle with the arm instead of hanging straight down. This created an increase in falling distance and centrifugal force, both of which contributed to greater power. These improvements helped the trebuchet maintain dominance on the battlefield.

3. Attach diagonal braces with 3/4 " #6 screws and glue.

The earliest trebuchets were "traction trebuchets [which] were invented in China in the 5th - 3rd centuries B.C.E. Traction trebuchets used human labor instead of a counterweight for power.

The Chinese needed so much power for the trebuchet that they had up to 250 solders pulling on ropes to operate the machine.

This machine could throw stones up to 100 meters, but was not very accurate, given the inherent inconsistency in using true manpower.

References

The Trebuchet in Action!

Medieval battlefields consisted mainly of sieges to fortified cities by some hostile force. Actual hand-to-hand combat was quite rare and usually only occurred during midnight counterattacks by the besieged or when the walls of the city were finally breached. Consequently, trebuchets dominated the battlefield with their ability to fling 300 lb. stones up to 275 meters, obliterating walls in their path.

In order to maximize their chance of winning, both the attackers and defenders employed trebuchets to help their cause. However, since the trebuchet is much easier to aim at a large stationary target than small mobile targets, it was usually much more effective for the side laying siege.

Step 2

Trebuchets also worked better against a fortified position because of the types of ammunition they employed: metal or stone balls, heads, corpses, dead animals, excrement, trash, and even Greek fire - a powerful burning-liquid weapon that could not be put out with water.

Most of these items were meant not to destroy walls, but to humiliate the enemy, taint their water supplies, and spread death and disease. One of the worst cases of such early chemical warfare came in the 14th century when Mongols fired corpses that contained the Black Death into the city of Kaffa. Kaffa was a port city, so the disease soon spread across the Mediterranean and into European ports.

Now let's assemble the trebuchet base!

1. Use white glue and screws to attach main uprights to one of the small base stands.

4. Attach trigger plate to end of base. Make sure the slot is up and aligned as pictured.

Image 2

Image 1

The addition of a fixed counterweight was a major advancement in trebuchet technology. This counterweight was affixed to the end of the shorter arm and, without the need for ropes and people to pull the machine, space was available for lengthening the sling, which allowed the projectile to go even farther.

Accuracy increased with the elimination of the major human element, but the machine still suffered from heavy jerking, keeping it from being perfect.

Start with one screw and then make sure the uprights are at 90 degrees (right angle) to the base stand and they align with the outer edge.

Tighten both screws.

2. Set the main base on the three base stands as shown. The two end pieces are aligned with the end of main base.

The piece holding the uprights is placed at the distance indicated. (Distance is important).

Fasten with 1 1/4" #6 screws and glue.

http://www.real-world-physics-problems.com/catapult-physics.html

http://hila.webcentre.ca/projects/trebuchet/base.htm

http://illumin.usc.edu/printer/140/the-trebuchet/

http://en.wikipedia.org/wiki/Trebuchet#External_links

https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&docid=kKwlm0dr61wYAM&tbnid=O8dkkfPxZMbJYM:&ved=0CAQQjB0&url=http%3A%2F%2Fwww.stormthecastle.com%2Fcatapult%2Fdevelopment-timeline-of-the-catapult.htm&ei=MhbBUcXXI4j7rAGkl4CYDw&bvm=bv.47883778,d.aWc&psig=AFQjCNGTKwBoClclejcSGPJaKyjfKg1rRw&ust=1371695002455470

http://library.thinkquest.org/05aug/00627/history.html

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Trebuchet.html

Goal

The fixed counterweight eventually gave way to a hinged counterweight. The hinge greatly increased the efficiency of the motion involving the counterweight, causing more power to be delivered to the projectile.

The hinge also helped to slow down the system when it reached the bottom. By slowing down the system, the trebuchet experienced less strain, increasing the life of the machine and decreasing the jerking forces.

Also, the newfound stability meant that the trebuchet did not have to be repositioned after every shot, so firing time improved to about twice per hour.

Step 3

Building the sling!

Hooray!!!! You did it! You have completed the steps to building a trebuchet.

1. Tie string around the 4 nails on the sling template.

2. Cut a 10 cm piece of duct tape, center it sticky-side up under the strings.

Press the strings into the tape.

Before you use the trebuchet you may want to go over the next installment on safety. For your viewing pleasure there is a clip to see what fun you will have!

3. Cut a second piece of tape and tape it over the first, capturing the strings.

4: Pull one nail to release the string.

Check out more fun videos (if you choose)

5: Cut two narrow strips of duct tape, use them to shape the duct tape into a pouch.

There is LOTS of fun and even some learning that can take place with this! Good luck with your build!

Final Assembly!!!

1: Use a loop of wire to attach one end of sling to hole in bottom of throwing arm.

2: Shape a loop of wire so that it easily slides in and out of release slot. Attach this wire to other end of sling.

3: Pull throwing arm to loaded position. Tape a loop of wire to the back of the pouch so that it protrudes through the slot in the trigger mechanism.

4: Use a straightened paper clip as the trigger pin. Attach a string to it so you can pull from a safe distance.