Bridge Strength (Truss)

We ran the project with a small group of year 4 & 6 students (age 8 & 10) in an afterschool 3D printing club, we believe that it will be manageable for year 5+ students. Some year 4 students may find it a bit more challenging.

• Working with a PC or laptop
  (PC environment, mouse & keyboard controls, working with a web browser, working with files and folders)
• Basic knowledge of geometry
  (basic knowledge of shape names 2D and 3D)
• Sketch independently using draft/graph paper (optional)

The aim of this project is to teach students which shapes are strong and weak. Furthermore it will teach them basic architecture/engineering skills, finding out what kind of structure works best for making simple bridges. In addition to this they will learn how to use CAD/CAM software and understand how 3D printing works from start to finish with the physical product at the end. The competition on whose bridge will hold the most weight will provide a fun and competitive experience. If their bridge services the weight they will be able to keep the bridge that they have designed.

Goals related to 3D printing

• Introduction to 3D printing
• Learning the basics of 3D modelling in TINKERCAD
• Export of models to STL format
• Introduction to 3D printer operation

Other goals

• Basic architecture/engineering skills
• Learn what shapes are strong/weak
• Learn how to use CAD/CAM software

• Standard IT classroom equipment with 3D printer or any classroom with laptops
• PC/laptop with a spare USB slot
• PrusaSlicer software installed on individual PCs/laptops
• Projector connected to the teacher's PC/laptop to present instructions, or synchronous creation of 3D models of the teacher and students (optional)
• Graph/Draft paper, rulers and pencils to sketch bridge designs (optional)

Project preparation by the teacher (approx. 3 hours 30 mins. Including printing of a sample body of 2 hours 30 mins)

• Approx 1 hour modelling of one sample object in TINKERCAD (model for demonstration, testing the work with TINKERCAD for synchronous teaching with students)
• Printing of a sample body (see approximate printing time)
• Print step-by-step guide

Approximate printing time for different scale factors

(fill setting 15% and 0.15 mm layer height)

• 95% Scale factor - 6h
• 80% Scale factor - 4h30min
• 60% Scale factor - 2h30min
   

Creating the project with a class (6 x 55min.)

The length of the project may vary according to the abilities and skills of students and the program may be condensed into less lessons if students find it easy.

• First lesson - 55 min
  • Introduction to the project and goal of the lesson  (5 min.)
  • Brainstorming - What makes a bridge strong/What shapes are strongest  (5 min.)
  • Introduction to modelling in TINKERCAD with tutorials (45 min.)

If TINKERCAD skills are not ready do not move onto second lesson.

• (Optional) lesson - 55 min
  • Reminder of project goals and assignment of bridge planning (10 min.)
  • Independent activity on draft/graph paper planning bridge design (45 min.)
     
• Second lesson - 55 min.
  • Reminder of project goals and assignment of individual projects (10 min.)
  • Independent activity in AUTOCAD TINKERCAD creating bridge base (45 min.)
     
• Third lesson - 55 min.
  • Reminder of project goals and assignment of bridge walls (10 min.)
  • Independent activity in AUTOCAD TINKERCAD creating bridge walls (45 min.)
     
• Forth lesson - 55 min.
  • Reminder of project goals and assignment of bridge top (10 min.)
  • Independent activity in AUTOCAD TINKERCAD creating bridge top (45 min.)
     
• Fifth lesson - 55 min.
  • Export STL file from modelling software (5 min.)
  • Launch and demonstration of working with PrusaSlicer software adding supports (40 min.)
  • Setting and exporting to G-code and copying source files to USB stick (10 min.)

Print students' bridges over several days and nights. (depends on how many students)

• Sixth lesson - 55 min.
  • Reminder of project goals (5 min.)
  • Applying weight to printed bridges (45 min.)
  • Evaluating whose bridge was the strongest and why (5 - 10 min.)
     

Project Structure (Lessons - 6x 55 min.)

The length of the project, especially for the lessons of the creating bridge parts, may vary according to the abilities and skills of the students and the program may be condensed into 4 lessons.

First lesson - 55 min.

• Introducing the project and the goal of the lesson (5 min.)
  What, why and how? Presentation of the project by the teacher.
• What makes a bridge strong/what shapes are strongest (5 min.)
  Introductory brainstorming with students about different shapes and their strengths. Shapes can be sketched on board as well as 3D printed shapes can also help visualise.
• Introduction to modelling in TINKERCAD (45 min.)
  It is a good idea for the teacher to use a smart whiteboard/projector to show the activity that the students will be doing. You can also use the projector to describe the individual steps that students will be doing.
  
  
  • Students will launch any web browser and enter the address tinkercad.com in the address bar, where they register and log in to the system. The program allows you to log in using Google Accounts as well, so it is possible to use school accounts if the school has them available.
  • Introduction to the TINKERCAD user interface and individual functions needed for basic modelling, control and setting of views. 
  • Students will follow some of the TINKERCAD tutorials to learn the basic shapes in the menu and try to resize, copy objects, move or create holes and change viewing angles.
    
     
• Check student progress in TINKERCAD tutorials to see if they can move onto the next lesson (5 min.)

(Optional) lesson - 55 min

• Introducing the project goals and the assignment of bridge planning (10 min)
  What the students should be aiming for. Explain and show how to use graph paper to plan the bridge design.
• Independent activity for planning the bridge design on graph paper. (45 min)
  
  
  • Using a pencil, ruler and graph paper the students will draw out the side profile of the bridge and a top down view of the bridge.
  • Make sure the students use the graph paper squares correctly. I find that each big square can represent 10mm which seems to work very well. But it's up to you how big or small you want the designs of the bridges to be.

Second lesson - 55 min.

• Assignment of individual work and reminder of project goals (10 min.)
  The teacher will explain the aim of the lesson - the creation of a bridge that will be tested how strong it is with weight applied. They will create the first part of the bridge (the bridge base).
• Independent activity in TINKERCAD (45 min.)
  Students will work individually creating the base of the bridge. Alternatively, the teacher can go step by step with the students creating the base of the bridge at the same time projecting it on a whiteboard.
  
  
  • Please use the step-by-step guide for specific 3D modelling instructions.

Third lesson - 55 min.

• Assignment of individual work and reminder of project goals (10 min.)
  The teacher will explain the aim of the lesson - the creation of the bridge walls.
• Independent activity in TINKERCAD (45 min.)
  Students will work individually creating the walls of the bridge.
  Use the same steps as lesson 2 just with creating the walls with slight differences.
  
  
  • Use the step-by-step guide for the differences in creating the bridge wall.

Forth lesson - 55 min.

• Assignment of individual work and reminder of project goals (10 min.)
  The teacher will explain the aim of the lesson - the creation of the bridge top.
• Independent activity in TINKERCAD (45 min.)
  Students will work individually creating the walls of the bridge.
  Use the same steps as lesson 3 just with creating the bridge top with slight differences.
  
  
  • Use the step-by-step guide for the differences in creating the bridge top.

Fifth lesson - 55 min.

• Export of STL file from TINKERCAD (5 min)
  Students proceed together, according to the instructions of the teacher, who can also mention the advantages / disadvantages of different export formats.
• Starting and demonstration of working with PrusaSlicer (40 min)
  Students will be shown how to add supports/enforcers to the bridge before exporting the g-code. The teacher will show what settings to use when creating the g-code (using brim, infill percentage). Then students will work individually on adding supports.
• Setting and export to G-code (10 min.)
  Students will export the g-code and save it in a shared folder or USB (depends on how you want to store the files).

Print bridges over several days (or over night depending on your preference).

Last lesson - 55 min

• Reminder of project goals (5 min.)
• Testing the strength of the bridges (45 min)
  Placing the bridge between 2 tables and dangling a bucket underneath with weights keeping track how much weight is added each time.
• Evaluating whose bridge was the strongest and why (5 - 10 min.)
  Talk about each bridge and understand why the winners bridge did better than everyones else.