The object of this project is to design, build, and operate a trebuchet that can launch a golf ball as far as possible. The trebuchet is to be built from the Erector Set which you used for the squash ball catapult. We will provide the golf ball.
Your team's tasks include:
- Designing the trebuchet from the parts in the Erector Set. You will have to supplement the kit with some type of sling and basket to hold the golf ball, and some sort of counterweight to provide the energy source for the trebuchet. The total cost of any additional parts shall not exceed $6.50. The design must be such that the golf ball can be launched repeatedly. The device you design can be operated from top of a cart, or from the ground. The counterweight and the length of the sling are important variables - your team must address how to vary or how to fix these quantities. The release procedure should allow the ball to be shot in a smooth and reproducible manner.
- Constructing the trebuchet.
- Taking data on the trajectory of the ball being launched as a function of either the counterweight or the length of the sling.
- Determining the performance map of the trebuchet from this data. That is, your team must establish the relationship between the length of the trajectory as a function of the counterweight or the length of the sling.
- Carrying out an analysis of the trebuchet using your knowledge of conservation of energy and rotational motion from physics.
- Demonstrating the performance of the trebuchet.
The final design and the design process must be documented by the team. The design, design process, modeling and analysis, and results of the final launch must be put in a final report. The final launch will be carried out on the day of the final, and the report will be due that day as well. There are more details on this at the end of this page.
The trebuchet was a siege engine that ultimately replaced the catapult in medieval war campaigns, mainly because the trebuchet could hurl heavier objects longer distances than the catapult. It uses a counterweight as the means of propulsion. The counterweight is attached to a pivoting arm, and as the counterweight drops, a flexible sling attached to the other end of the pivoting arm is swung into motion. The sling holds the heavy rock, or diseased cow, or some other horrible missile which is released from the sling near the top of its rotational motion. The trebuchet can throw remarkably heavy objects considering its very compact form. A very interesting article on the trebuchet appeared in the May, 1995, Scientific American. In addition, one can find an enormous amount of information about trebuchets on the WWW. For example, here some sketches of a weight powered trebuchet in various "states". This first figure shows a trebuchet just before launch. This second figure shows a trebuchet just as the sling is about to be lifted. And this third figure shows a trebuchet just as the projectile is launched. Another view, of an actual scale model trebuchet, made from sturdy wooden parts is shown here.
Lee Rhodes, a senior in mechanical engineering, has put together an Excel spreadsheet to model the performance of a trebuchet. It assumes that the attached counterweight drops vertically and does not act as a second pendulum. It also assumes that the applied torque is constant with time, and rotational kinematics can be applied to determine the angular positions as a function of time. You may use (or modify) this spreadsheet.
On the day of the final, several evaluations will be carried out - some you will directly perform (either as individuals, or as teammates), and one carried out by the Foundation Coalition instructors to assess your performance on this project (and thus in this class). In order to help you with the assessment activities, it is necessary for you to understand the pedagogical concept of level of learning. The levels of learning (LoL) were first enumerated by an educator named B. Bloom who described these levels in a book entitled Taxonomy of Educational Objectives published in 1956. Sometimes the LoLs are called Bloom's Taxonomy. They are listed in brief in this table:
|Level of Learning
Making use of ideas without relating them to other ideas
Restating ideas in ones own words
Being able to use an idea, method without being told to use it
Applying laws of math, physics, etc., to practical situations
Working project-type problems
Being able to explain why
Explaining reasons for conclusions
Describing causal relationships
Putting together parts and elements into a unified organization
Developing a model
Proposing or creating a design
Judging the value of ideas, processes using appropriate criteria
Determining which modeling approach is best for one's needs
Deciding whether a design is feasible
Determining whether an object possesses quality
With these points in mind, the assessment activities can now be described.
Assessment of another team's trebuchet
Since your team has gone through the process of designing, constructing, analyzing, modeling, testing, evaluating, modifying, and describing your trebuchet, you have learned a great deal about this machine. You, as individuals and as teams, probably know more about trebuchets than all others at ASU - perhaps even in Arizona. So you therefore are well poised to assess the quality of another team's trebuchet. In other words, although you may have reached only the comprehension level in some of the specific topics in other areas of this class, you are approaching the evaluation level in this area.
So, during the trebuchet shoot-out, we would like you to carry out an evaluation of another team's trebuchet. To carry out this evaluation, we would like you to use a Kepner-Tregoe decision analysis procedure using this blank KT form. You get to determine the "musts" and "wants" categories for the analysis. To make this process go smoothly, make up the KT table in advance of the shoot-out.
You must interview the team to decide which LoL the team has achieved in each of the "wants" categories. Can the team describe what it has done (Knowledge, Comprehension)? Can the team describe why it has done some activity (Application, Analysis)?
On the day of the shoot-out, observe the performance of team's trebuchet and then carry out the interview and KT analysis. During the afternoon of the final exam, use your team's joint writing skills to write this evaluation and attach it as an appendix to your own report.
Assessment of your teammates' individual performance
We would like each of you to evaluate your own and your teammates' performance in this last project. It is a very simple process. You imagine that your team is a "company" that designs and manufactures trebuchets. You have a total of $40,000 to distribute as "salaries" to each team member, including yourself. On the salary form, assign a salary to each team member based on your own perception of that team member's contribution to the team. The sum of all salaries, of course, must add to $40,000. Do not show your evaluation to your teammates - it is supposed to be an anonymous process. Turn these evaluations into Prof. Roedel - inside a sealed envelope.
Assessment of your own team's performance
After the demonstration of all of the trebuchets, you will return to the classroom and prepare:
- Your final report
- The completion of the KT form and the Appendix describing your assessment of the other team's machine
During this time, you will also be interviewed by a panel of Foundation Coalition faculty. The interview will be brief - approximately 15 minutes in length - and the panel members will ask you and your teammates questions about the design and operation of your trebuchet. The questions will probe the levels of learning you have attained in this project, and your answers will be factored into your grade in the FC courses.
At the end of the interview, you can return to the classroom and carry out the following tasks:
- Complete your reports.
- Return your Vizability textbooks.
- Dismantle the trebuchets, put the parts back in the cases, and return the erector sets.
When you have submitted the reports to Prof. Roedel (as a .doc or .htm file on a disk) and returned the other items, your FC Semester is finished!