Introduction .:. Statement of the Problem .:. Hypothesis .:. Variables .:. Method .:. Materials .:. Graphs and Data

 Single Arm .:. Spring Arm .:. Means .:. Results .:. Conclusion .:. Bibliography .:. Links

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Introduction:

Trebuchets were the original weapon of mass destruction. They were used in warfare to hurl anything the attacker wanted to at their enemy, including giant boulders to break down the castle walls, dead animals meant to spread disease and giant fireballs. “It is generally believed the trebuchet was invented in China in centuries BC, but it never showed in Europe until around 500 AD. In Europe trebuchets were first used in Italy in the 1100s, and were introduced to England in 1216 during the Siege of Dover” (Medieval Period). Previously, no siege machine had existed with such huge proportions, before the trebuchet, catapults were used to hurl items, and while they were still used as after the invention of the trebuchet, they weren’t anywhere near as powerful as the trebuchet. “A typical medieval trebuchet could hurl a 300-pound rock 300 yards. A series of these projectiles could bring down even the most fortified castle walls and crush any soldiers in the way” (eHow) and was so effective it was still in use “100 years after the introduction of gunpowder” (NF Observatory).

The general mechanics of a trebuchet are relatively simple. They work by creating a massive amount of potential energy and then converting that into a massive amount of kinetic energy. "The trebuchet is energized by lowering the long arm and raising the weighted short arm, usually with a winch, and is locked into the charged state by a trigger mechanism (cocked)” (MedievalWarfare.com). This energy was stored in a rope that was wound tightly and often would require several men to tighten the rope. When a switch was triggered, the rope would release, and the trebuchet would fire. A trebuchet is almost always built with a counterweight on the opposite side of the launching arm in order to create a higher amount of potential energy. When firing, “The counterweight, pulled by gravity alone, rotates the [launching arm]. The [launching arm] pulls the sling….The sling accelerates and holds the projectile until release” (Redstone Projects).

While there are many factors that can influence the range of a trebuchet, our group is interested in determining how acceleration affects range. From our observations and research, we have noticed that trebuchets with a heavier counter weight create a faster acceleration and would throw objects farther. So we derived that if we could create and arm that accelerates the object faster, the object would go farther. “The trebuchet has the greatest angular acceleration at 0 degrees and afterwards the acceleration drops” (Radlinski). This means that the majority of the acceleration is created during the initial moments of the trebuchet’s launch. Our plan is to attach a spring to the throwing arm and divide it into two parts. Theoretically, the spring should pull the object with a faster acceleration to its launch resulting in a farther distance thrown. This arm can almost be seen as a catapult on the end of a trebuchet’s arm. The spring’s added acceleration boost at the end of the launch may be able compensate for the imbalanced time that acceleration is created, and create a “bonus” force to launch the object farther. In order to create an equal test, we will have to ensure the same conditions, such as counter balance weight, are set for each launch for both the normal arm and spring arm.

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Statement of the problem:

The purpose of this investigation is to determine whether or not a spring arm will increase the distance an object is thrown by a trebuchet, in comparison to a traditional armed trebuchet.

 

Hypothesis:

We believe that if a spring arm is installed on a trebuchet it will have a greater range than a regular arm, although at lower weights, the regular arm will have a greater range due to a difference in arm weights.

 

Variables:

Independent: The amount of weight used as counterbalance.

           

Dependent: The distance projectile travels.

 

            Control: The arm that we used and the starting place of each launch.

 

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Method:

            Once we built the trebuchet we brought it, the tools and the materials to the Tualatin high school football field. We set the trebuchet up so it would launch the ball down the field, we also set up tape measures down so we could measure the distance of each launch. We put on the weights on one end of the arm using the weight rack design to help secure it.  We then pulled down the arm and loaded the ball in the sling. Then we attached the sling to the launching mechanism and set the firing mechanism. Then we pulled out the string holding the arm down launching the 2 kg projectile.  Finally we recorded our measurements of the launch. Once we had all our data points for that data set we adjusted our weight according to the next weight level and repeated our process. We did five launches per weight class that went from 100 lbs to 250lbs. Once we finished with our first arm we had to unbolt the two blocks on top of the support beams, remove the first arm and then replace it with the second arm.  After replacing the arm we secured it and then completed the process again.

 

List of Materials:

-Wood                                     -Bolts                                       -Screws

-Canvas                                   -String                                      -I Bolts

-Metal Nipples             -T connector                            -Caps

-Black Pipe                              -Measuring Tape                      -Washers

-Wood Working Tools (table saw skill saw, reciprocating saw, square angle, etc…)

-Socket Wrench                       -Rubber Mallet             -Screw Driver

-Giant Spring                            -Threaded rod                         

 

 

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Graphs and Data-

 

 

Diagram of our Trebuchet-

 

 

     

 

        Single Arm-

 

Single Arm Trebuchet Data-

 

	100 lbs	150 lbs	200 lbs	250 lbs
Trial One	19.5m	23m	30.5m	35m
Trial Two	13.5m	28m	29m	31.5m
Trial Three	17m	26m	34m	34m
Trial Four	17.5m	24.5m	33.5m	37m
Trial Five	18.5m	29.5m	32m	33m
Mean	17.2m	26.2m	31.8m	34.1m
Uncertainty	1.2	1.3	1	1.1

singlearm.txt .:. singlearm.xls

           

 

 

 

Single Arm Graph-

 

 

 

           

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   Spring Arm Trebuchet-

 

Diagram of Spring Arm Trebuchet

 

 

Spring Arm Trebuchet Data

 

	100 lbs	150 lbs	200 lbs	250 lbs
Trial One	2m	9m	24m	28.5m
Trial Two	4m	13.5m	26.5m	31.5m
Trial Three	0m	11m	24.5m	27m
Trial Four	3m	9.5m	19.5m	32.5m
Trial Five	4m	7m	22m	30m
Mean	2.6m	10m	23.3m	29.9m
Uncertainty	0.8	1.3	1.4	1.1

spring.txt .:. spring.xls

 

 

Spring Arm Trebuchet Graph-

 

 

 

 

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   Compare the Means-

 

            Data of the means of each trebuchet

 

	100 lbs	150 lbs	200 lbs	250 lbs
Mean of Single Arm	17.2m	26.2m	31.8m	34.1m
Mean of Spring Arm	2.6m	10m	23.3m	29.9m

means.txt .:. means.xls

 

 

            Graph of the means-

 

 

 

 

Calculations-

           

 Mean- To calculate the mean, we used the formula

(Data Points!/The number of data points)

           

            Uncertainty – To calculate this, we took the shortest launch of each weight trial

and subtracted it from the farthest distance, then divided it by five, the number of trials we did. ((High-Low)/number of trials).

 

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Results-

After doing all the launches, the spring arm was unable to reach the distance that the regular arm did, even at the same weights. Something we noticed was that the slope of the spring arm trebuchet was almost twice that of the single arm. Theoretically, if we added another 50 pounds, the spring arm would have thrown farther, but our trebuchet would have broken under the weight.

 

 

Conclusion:

 

            Our results showed that the spring armed trebuchet did not go as far as the single armed trebuchet, but the spring armed trebuchet had a higher slope of trajectory. Half of our hypothesis was supported, the spring arm did not have a greater range than the regular armed trebuchet but the regular arm did surpass the spring arm in the lower weight as we predicted. For the spring arm, building momentum at the beginning of the launch is imperative in order to produce a reliable shot. While the potential energy that is built up in the spring does help snap the ball a little farther when it is changed to kinetic energy, extra weight is needed to compensate for the weight of the spring arm to gain the velocity it needs. If the weights do not get the arm moving, as in what happened with lower weight tests, the launch of the projectile will not be as far as predictions show it to be. For the single armed trebuchet, the different weight easily and effectively rotated the arm because of its lower weight. Some sources of error may be contributed to the wind, an inconsistent release mechanism, weights hitting the side of the structure while firing, and the bending of the pipes. Some of the improvements may include building the trebuchet with a higher weight capacity, make a more consistent firing and release mechanism.

 

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Bibliography:

 

Medieval Period. "Medieval Trebuchets". Medieval Period.com. 22 November 2009 http://www.medieval-period.com/medievaltrebuchets.html

 

Ninomiya, Kent. "How Does a Trebuchet Work?". eHow.com. 22 November 2009 http://www.ehow.com/how-does_4566869_a-trebuchet-work.html

 

            NF Observatory. "The Trebuchet". NF Observatory. 22 November 2009 http://www.nfo.edu/trebuche.htm

 

            Medieval Warfare. "Medieval Warfare during the Cathar Crusades". MedievalWarfare.com 22 November 2009 http://www.medievalwarfare.info/121343_perriers.htm

 

TrebuchetStore.com. "How a Trebuchet Catapult Works".

RedstoneProjects.com 22 November 2009 http://www.redstoneprojects.com/trebuchetstore/how_a_trebuchet_catapult_works.html

 

Radlinski, Filip. "The Physics of a Trebuchet". Radlinsky.org. 1995.

22 November 2009 http://radlinski.org/trebuchet/7_fig5_7.html

 

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Links:

 

http://www.medieval-period.com/medievaltrebuchets.html

We chose this website because it was a good place to learn about the general history of the trebuchet.

 

http://www.medievalwarfare.info/121343_perriers.htm

This site was really helpful in learning about all the different types of trebuchets and where we gathered information on how to create our design.

 

http://www.redstoneprojects.com/trebuchetstore/how_a_trebuchet_catapult_works.htm

This site is all about how trebuchets throw objects and also helped us design our prototype arm.

 

 http://radlinski.org/trebuchet/7_fig5_7.html

We used this site to find out the best way to launch our trebuchet.

 

http://www.ehow.com/how-does_4566869_a-trebuchet-work.html

We chose this website because it was helpful in learning how trebuchets work

 

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