# Mousetrap Cars A basic and refresher workshop for this Mechanical Engineering Challenge.

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Mousetrap Cars A basic and refresher workshop for this Mechanical Engineering Challenge

Bonus Points for whoever knows this game…!!!
OK… Now Let’s Dig In…!!! Bonus Points for whoever knows this game…!!!

What is a Mousetrap Car? A mousetrap powered car is a vehicle that uses a mouse trap for a motor and a string to transmit force. In this method one end of a string is attached or tied to the arm/bail on the mousetrap and the other end of the string is wound around an axle. By winding the string around the axle, the mouse-trap's spring is wound creating stored/potential energy. When the mousetrap car is released the mousetrap’s spring unwinds the string off of the axle causing the wheels to turn and off the vehicle goes.

Purpose & Objectives of this Session
Encourage and promote the integration of STEM standards into the building and designing processes of the mousetrap car Explain Guidelines of the competition Help you teach your students: Problems solving skills How to budget their time Cooperative behavior Engineering and design concepts Let’s Focus On

STEM [ideas] of Mousetrap Cars
Torque Potential & Kinetic Energy Speed Wind drag Rolling Friction Rotational Inertia Scientific Inquiry Science Tradeoff Concepts Simple Machines Materials Research Build Techniques Technology Redesign Troubleshooting Testing Assembly Design Processes Engineering Measurements Manipulating variables to Maximize F (See Formula) Manipulating variables to maximize N (See Formula) Mathematics

Building a Winning Team
A “Solid” SECME Mousetrap Car team is composed of a combination of students with different skills and abilities i.e. Researcher / Planner Drafter / Designer Builder / Tester The coordinator should monitor student progress to assure that they understand the STEM concepts, follow the guidelines, and meet deadlines.

Calculating the Score [Overall]
The overall team score in the competition is a sum of the following: Performance > [Max 100 points] Technical Report > [Max 100 points] Design Drawing > [Max 50 points] Team Interview > [Max 50 points] NOTE: Team Interview will have a 75 pts max for the National competition (see guidelines)

Evaluation Guidelines
REQUIREMENTS Each Mousetrap Car Engineering Design team must have three (3) students & competition requires participation in these four areas: Mousetrap Car Construction and Run Technical Report on Mousetrap Car Design Drawing of Mousetrap Car Team Interview with Judges

Evaluation Guidelines
CAR CONSTRUCTION AND DESIGN This is an overview [* * *Read Official Guidelines Carefully* * *] A standard mousetrap MUST be used (4.5x10cm & ~ 25g) Understand the components of a standard mousetrap The mousetrap spring must be the sole power source Original mousetrap spring and base must remain intact and unaltered. Locking lever and bait holder may be removed. Bail may be straightened but unaltered. NOTE: For experienced builders, gears & pulleys are allowed as long as ALL the other guidelines are adhered to.

Evaluation Guidelines (cont)
CAR CONSTRUCTION AND DESIGN This is an overview [* * *Read Official Guidelines Carefully* * *] The spring must be visible and/or accessible for judges. The car must have a minimal of 3 wheels Cars will be tested on a smooth flat surface. Distance is measured from the farthest point of travel, utilizing a straight line to connect the two points. There will be two (2) runs for each car; the better performance run will be used for the final scoring

Standard Mousetrap Diagram

Calculating the Score [Performance]
It’s time to some numbers…! Two (2) formulas are used to calculate the Performance score for the car’s run: I’m getting hungry…!

Solving for N w = mass of the mousetrap (25 grams)
W = total mass of completed car (in grams) D = distance (measured in a straight line from starting point to stopping point in centimeters) L = length of car in centimeters (furthest of front to furthest of rear) T = time (seconds) cars travels from start to stop N = Performance score

Solving for F N = Performance score from
NL = maximum performance score of all cars F = Final Performance score (to be combined with Technical Report, Design Drawing, and Team Interview scores)

Key Points to Consider with (W)
A good mousetrap car is designed around the two (2) formulas and not around just how far it can go. W = total mass of completed car (grams) Your goal is for the total mass/weight of the car to be as LOW as possible and can be achieved by: Decreasing the mass of the wheels (cut out insides) Choosing light building materials (glue, tape, foam, etc.) Minimize decorative paint, tape, stickers, etc.

Key Points to Consider with (D)
D = distance (measured in centimeters) Your goal is for the mousetrap car to travel as far as possible… In a straight line…! Regardless of the car’s path, the value of D is measured from the starting point to the end point utilizing a straight line. In the examples below, A and B are the start and end points, respectively, with D being the actual distance. NOTE: There are NO required minimum or maximum distance(s) to travel

Key Points to Consider with (L)
L = Length of the car (from the furthest of front to the furthest of rear) measured in centimeters Your goal is the minimize the length of the car while retaining the properties that make it perform well

Key Points to Consider with (T)
T = Time (measured in seconds) Your goal is for the mousetrap car to travel as fast as possible… In a straight line…! Speed is calculated as distance divided by time. Your goal is for the car to not only travel as far as possible (distance) but to also arrive at your maximum distance with the lowest time which essentially means the cars is FAST…!!!

Now Let’s Dive Into Some Examples…

Analysis of Mass Calculation (W)
W = 45 grams W = 40 grams N = (.625) x (250) + (250) N = N = N = (.555) x (250) + (250) N = N = A small decrease of 5 grams of (W) increases the (N) value by 4.47%

Analysis of Time Calculation (L)
L = 15 cm L = 10 cm N = (.625) x (166.66) + (250) N = (.625) x (250) + (250) N = N = N = N = When the longest dimension (L) of the car is decreased by 5 cm, (N) increases by 14.7%...!

Analysis of Time Calculation (T) (D/T = Speed)
T = 15 sec T = 10 sec N = (.625) x (250) N = (.625) x (250) + (250) N = N = N = N = If you decrease (T) by 5 seconds your (N) value increases by 25.81%...! Speed Up…!!!

Technical Report Guidelines
As a part of the Design Competition, the team is required to write a Technical Report describing the design, construction, and operation of the Mousetrap Car. Parts of the Technical Report are: Structure Table of Contents Abstract Introduction Design NOTE: Please see Official Guidelines for specific details Construction Procedure Operation Conclusion/Recommendations Acknowledgements (Optional) Appendix (sketches/tables/charts) ALSO NOTE: Take EXTREME caution regarding plagiarism

Design Drawing Guidelines
The mousetrap car drawing in required to illustrate the actual car built (photographs or computer generated drawings will NOT be allowed). The size of the engineering paper is to be the standard ANSI C 17” x 22”, plain, non-grid, 16 pound vellum sheet. Allow the required 1” border on all sides. Actual drawing is to cover an exposed area of 15” x 20” of the paper. NO MOUNTING OR FRAMES BUT DRAWING MAY BE LAMINATED FOR PROTECTION IF DESIRED. All dimensions are required to be illustrated on the drawing

Design Drawing Guidelines
4) The scale and the units are required to be indicated on the drawing 5) The team’s Mousetrap Car Drawing is required to show front, side, and top views 6) All parts of the car are required to be labeled. 7) Ink pens, pencils or markers may be used

Design Drawing Guidelines
8) The title legend is to be drawn in the bottom left corner of the drawing inside the 1” border with the following information: Team name School Name School District Team Member’s Names and Grade Levels School Coordinator’s Name Date of Competition AT ALL COMPETITIONS, THE MOUSETRAP CAR DRAWING WILL BE JUDGED ON: (See guidelines for details) 1) RESEMBLENCE (Between the actual mousetrap car and drawing) 2) SCALE 3) NAMING/LABELING (of all of the parts used) 4) APPERANCE/NEATNESS

NOTE: Please see Official Guidelines for specific details
Team Interview Each student team will be interview by a panel of judges discussing the car’s design and testing as well as the Design Drawing & Technical Report Team members are interviewed as a group Each member is expected to be able to serve as spokesperson The interview will be conducted apart from the performance and scoring of car NOTE: Please see Official Guidelines for specific details

Team Interview The interview will take place between the Design Drawing and Technical Report scoring and performance runs The interview will be one element in arriving at the overall score in competition. The Team Interview will be judged on: - Teamwork - Application of Technical Principles - Knowledge of Design - Oral Communication Skills

Final Key Points Remember… STEM, STEM, STEM…!!!
Teachers should focus on STEM standards along with the design and build of Mousetrap Cars Teachers should ensure that students design, build, test, troubleshoot and rebuild as much as necessary to thoroughly grasp the STEM concepts regarding Mousetrap Cars in order to be ready for both Regional and National Competition Students should design and build their cars around the formulas to: Minimize the total mass of the car (W) Maximize the distance car travels in a straight line (D) Minimize the size of the car (L) Minimize the Time (T)… FAST CAR…! Remember… STEM, STEM, STEM…!!!

One Last Thing Please visit the National SECME website’s for more information and details and at Educational Resources – STEM National Standards Please enjoy some pictures on the next 4 slides…!

Pictures of Mousetrap Cars

Pictures of Mousetrap Cars
Decrease the mass of the wheels by cutting out the insides of large wheels

Pictures of Mousetrap Cars

Pictures of Mousetrap Cars
NOTE: Build Instructions Next

Materials for Construction
1 - Victor mouse trap, 2 - small screw eyelets 2 - CDs (rear wheels) 1 - dental floss 2 - front wheels (small black) 1 - zip tie 2 - red CD inserts 1 - small vinyl tubing (3.5mm) 1 - wood axle (¼” x 3½”) 1 - large vinyl tubing (5mm) 1 - metal axle (1/8 ” x 2 ½”) 2 - balloons 1 - drinking straw 1 - small brass nail (optional) 2 - large screw eyelets 1 - Phillip head screw (optional) Tools Super glue Ruler Pencil Pliers Hammer Scissors Push pin Clear tape

Preparing the body Remove the RED parts from the mousetrap Bail hook
Locking lever Staples/fasteners

Chassis Prep for Axles Turn mousetrap over to the flat blank side
0.8 cm Turn mousetrap over to the flat blank side Using the pencil and ruler, draw a parallel line 0.8 cm from each edge of the mousetrap Make sure the lines intersect

Chassis Prep for Axles 0.8 cm Front Wheel Axle Back Wheel Axle:
Flip side is mouse (V)

Preparing The Body Use the push pin to make holes at the intersections of the vertical and horizontal lines. Screw in the eyelets: small eyelets go on the mousetrap end with the writing Front Wheel Axle Small Screw eyes for Front Wheel Axle Back Wheel Axle: Flip side is V Large Screw eyes for Back Wheel Axle

Chassis Prep for Axles Small Silver Screw eyes for Front Wheel Axle
Back Wheel Axle: Flip side is V Large Gold Screw eyes for Back Wheel Axle

Install Axles Insert the metal axle into the small eyelets and wooden axle into the large eyelets Cut two ¼” pieces of the straw (or small tubing) and put on metal axle (outside of the small eyelets) Cut two ¼” pieces of the 1/8 clear tubing and put on wooden axle (outside of the large eyelets)

Chassis Prep for Axles Place the red CD inserts into the CDs.
Cut balloons into strips and place along the outside edge of the disk. Install CDs on both ends of the wooden axle Place the cable tie on the wooden axle in between the screw eyes (optional) NOTE: You will probably need to few dabs of super glue if the red CD insert spins/slides inside the CD and/or on the wooden axle

Transmission Take a dental floss and tie it to the middle of the bail
Place a little dab of glue on the string where it attaches to the bail The string length should extend the span 1.5 times the length of a mouse trap

Winding The Car If you use the zip tie, make a loop with the dental floss and put the loop over the zip tie If not, make an L shape and wrap the dental floss directly on the wooden back axle Wind the axle away from you tightly, gradually lifting the bail until it is all the way down Hold the bail down, put the car on the floor, release the bail and WATCH IT GO…!!!

The Formula and its components
w= the mass of the mousetrap= 25 g W= the mass of the completed mousetrap car D= the total Distance traveled straight from start to finish(in cm) L= the length of the car in cm T= the time of travel start to finish in seconds N= the total points N= (w/W) x (D/L) + (D/T)

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