Hands-on Activity Trebuchet Launch

Learning Objectives

After this activity, students should be able to:

• Design a LEGO MINDSTORMS EV3 robot that can be used to launch objects.
• Program a robot using LEGO MINDSTORMS EV3 software.
• Determine the distance an object travels and relate it to its respective weight.
• Design and carry out a controlled engineering experiment.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• LEGO MINDSTORMS EV3 robot, such as EV3 Core Set (5003400) at https://education.lego.com/en-us/products/lego-mindstorms-education-ev3-core-set/5003400#lego-mindstorms-education-ev3
• LEGO MINDSTORMS Education EV3 Software 1.2.1, free online, you have to register a LEGO account first; at https://www.lego.com/en-us/mindstorms/downloads/download-software
• computer, loaded with EV3 1.2.1 software
• 2-3 sheets of copy paper (recycled is fine)

Note: This activity can also be conducted with the older (and no longer sold) LEGO MINDSTORMS NXT set instead of EV3; see below for those supplies:

• LEGO MINDSTORMS NXT robot, such as the NXT Base Set
• computer loaded with the NXT 2.1 software

To share with the entire class:

• robot built from a LEGO MINDSTORMS EV3 kit
• access to a computer
• 1 eraser
• 1 tube of Chapstick®
• 1 tennis ball
• 1-2 gum drops
• 1 paper ball (made of a crumpled piece of printer paper)
• 1 ping pong ball
• tape measure
• scale

Worksheets and Attachments

Pre-Req Knowledge

Basic concepts of a how a trebuchet functions.

Introduction/Motivation

Who loves watching objects fly through the air? (Give students times to discuss among themselves.) The term launch is often used to describe how far an object can travel. Trebuchets are devices that can launch object through the air. They were designed during medieval times to throw payloads (heavy objects) at enemies. Believe it or not, friendly competitions exist in some areas today in which trebuchets are used to launch pumpkins and even pianos. During this type of competition, a team wins when their trebuchet launches a pumpkin the farthest. Can you imagine how far a trebuchet would have to launch a pumpkin in order to win? (Give students time to guess a distance.)

In this activity, you design and test a trebuchet—actually a robot—to determine how far an object will travel based on its weight. Then, you adjust the angle and the length of the robot arm and determine how far different objects will travel, given modified variables. Basically, through experimentation, you learn how to design the best type of trebuchet to launch a variety of objects.

Why are we learning about trebuchets? I'm glad you asked! Trebuchets are an important educational tool because they demonstrate several principles encountered in basic physics—a branch of science that studies matter and its motion. Today, we will use computers and robots to model some of these physics concepts.

So, in this engineering activity, you apply math and science to predict how objects move through air as you design, build and program your own robotic creation to propel objects through the air. You also learn the importance of a variable, which is something that can be changed. By changing one variable at a time, you can determine what makes an object travel farther. Let's start launching!

Procedure

Background

During the first century, the Romans figured out different ways to make projectiles reach a certain location. During battle, they had to reiterate their designs in real time so that objects they hurled reached their opponents. The Romans applied a great deal of math and science, as well as trial and error, to solve this problem; the result of their efforts was the design of a crude, but effective, trebuchet—a type of catapult. Today, we use the trebuchet for both advanced solutions, as well as for entertaining purposes, such as catapulting pumpkins in friendly competition.

Before the Activity

• Gather materials and make copies of the How Far Does It Go? Worksheet, one per student.
• Load the EV3 software onto the computer.
• Divide the class into groups of four students each and assign each group member one of the following tasks: Launcher Driver (launches the object); Launcher Passenger (prepares the launcher); Measurer (measures how far the object travels); and Recorder (records the data observed from launches).

With the Students

Part 1: Preparing the Robot

1. Have groups design their own robot launchers. Since many ways exist to design robots, tell students that this is an open-ended design project. (See some examples of student-designed projects in Figure 1.)

   

2. Have students build their own robots before moving on to the programming stage. Since no set of instructions are provided for building, encourage students to be creative and work together to come up with viable designs.
3. Following Figure 2, instruct students to program the robot to launch objects. If the program does not look like Figure 2, then instruct students to look in their pallet on the left side of the window for the program and make sure the motor, direction and power agree with Figure 2. The arrow in Figure 2 represents the direction, and the semi-circle filled with the orange color represents the power.
4. Once programmed, have students plug the cable into motor A, located on the EV3 brick.
5. Open the MINDSTORMS program and ask students to drag the motor block to the orange square; select the motor, power and direction. It is important that students understand they must have one motor do one rotation forward in order for the launcher to work.

Part 2: Preparing for the Launch

1. Review correct measurement skills with students and teach them how to measure distance.
2. Show students the variouis objects available to be launched, and ask them to predict which will travel the farthest.

   

3. Ask students: What do you think will happen to the object's travel distance when the arm angle is changed?
4. Ask students: What do you think will happen if you increase/decrease the angle or increase/decrease the length of the arm?

Part 3: The Launch

1. Show students the objects to be launched again. Have them use a scale to determine and record the weight of each object.
2. Direct students to take turns within their groups to launch objects. To do this, take an object and place it at the end of the arm for launching. (Note: Watch that students do not launch objects at each other.)
3. Once launched, have groups measure the distance traveled (that is, the distance from the robot to the object); be sure students know the weight of each object before they launch it.
4. Instruct students to record the object's distance traveled on their worksheets. Make sure they measure where the object first hits the ground, not where it rolls or slides to.)
5. Once all groups have obtained data for their first trials, change the variables, repeating steps #2-4 for each variable change. First, change the angle of the arm and next, return the arm angle to its original setting but change the arm length).
6. Direct students to complete the follow-up questions on their worksheets.

Vocabulary/Definitions

angle: The amount of rotation that separates two vectors.

constant: The quantity that remains constant in a given equation.

distance: The amount of space between objects.

length: The measure of how long something is from one end to another.

variable: The quantity that changes in a given equation.

Assessment

Pre-Activity Assessment

Guessing Game: Have students weigh the different objects. Ask them to predict which object will go the farthest, giving reasons for their answers.

Activity Embedded Assessment

Design a Robot: Direct students to design robots that will be able to launch objects. Explain that this is called open-ended design since there is no one right way. Ask them to explain to you how their designed launchers function to launch objects.

Post-Activity Assessment

Worksheet: Have students use the How Far Does It Go? Worksheet to record their trebuchet experiment data and results. Review their data, graphs and answers to gauge their level of comprehension.

Tuning the Equation: Ask students what happens when both the arm length and arm angle are changed? Ask them how far the object goes when these two variables are manipulated together.

Re-Design: Ask students to think about how changing variables (that is, the arm length and arm angle) affected their robot performances. As engineers, how would they re-design their existing robots to launch an object the farthest? How would they modify the design if accuracy was more important than distance?

Investigating Questions

• Which object went the farthest? Why? (Answer: The paper object went the farthest because it was the lightest.)
• What happened when the length of the arm was changed? (Answers: When the length of the arm was increased, the velocity and power of the object increased. Also when the length of the arm is longer, the angle of release is smaller. When the arm is shorter, the distance the object traveled is shorter; when the arm is longer, the distance that the object traveled is longer.)
• What happened when the angle of the arm was changed? (Answers: When the angle is smaller, the distance is shorter; when the angle is bigger, the distance is larger.)
• As engineers, what concepts did you apply to solve this problem? (Answers: We applied math, science and our own creativity to effectively design trebuchets; engineers incorporate all of these concepts as they design, analyze and iterate product designs.)

Safety Issues

• Remind students to only launch towards unoccupied space, never towards other people.

Troubleshooting Tips

Remind students to test their launchers before they begin to launch the objects.

Remind students that all launches should be precise; they should not estimate their launches.

The rubber bands on their robot launchers should have some sort of tension; students may need to adjust the tension after they have launched an object.

Activity Scaling

For upper grades, have students experiment with other materials, and launch them with different angles and arm lengths. Specifically, challenge students to create robots with long arms and find out what length impairs the function of the arm. Additionally, experiment to find out what arm length is not strong enough to launch an object and what length provides the best launch.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This activity was developed by the Applying Mechatronics to Promote Science (AMPS) Program funded by National Science Foundation GK-12 grant no. 0741714. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.